Prompt GeV-TeV Emission of Gamma-Ray Bursts Due to High-Energy Protons, Muons and Electron-

在海拔5000米以上地区利用单粒子方法探测γ暴实验构想--基于水切伦科夫技术刘茂元;厉海金;扎西桑珠;周毅【摘要】Ground extensive air shower experiment is powerless for detecting cosmic ray particles of tens GeV en⁃ergy renge in the GRBs (Gamma Ray Burst) so far, because of its threshold energy. The experimental altitude needs to be increased in order to achieve more effective observation. In the present paper, setting up a water Che⁃renkov detector array at 5200m altitude in Tibet was proposed and the idea of ground experiments on multi-GRB and tens of GeV photon observing can be achieved by using single-particle technology, and also can supportpre⁃dicting for large-scale experiments.%目前，对于伽玛射线暴（Gamma Ray Burst, GRB）的探测，地面广延大气簇射实验由于阈能原因，对几十GeV能区的宇宙线粒子探测无能为力，只有提高实验海拔才能实现更有效的观测。

文章描述了在海拔5000m以上地区建造水切伦科夫(WCD)探测器阵列，利用单粒子技术，来实现地面实验多GRB几十GeV光子的正观测设想，为大规模实验提供预言支持。

化学分析计量CHEMICAL ANALYSIS AND METERAGE第30卷，第1期2021年1月V ol. 30，No. 1Jan. 202192doi ：10.3969／j.issn.1008–6145.2021.01.019紫外可见分光光度法测定壁纸中甲醛的不确定度评定张艳艳，贾红丽，王萍，王光英，程建伟，赵岩，杨晓蕾，王建惠，曾盼，李钊(青岛市产品质量监督检验研究院，山东青岛　266000)摘要　采用紫外可见分光光度法测定壁纸中甲醛含量，对测定结果的不确定度进行评定。

依据GB 18585–2001《室内装饰装修材料壁纸中有害物质限量》标准，对壁纸中甲醛含量的检测过程进行研究，系统地分析了整个检测过程不确定度的来源，包括重复测定、样品溶液的移取、标准工作溶液的配制、标准曲线的拟合和测定仪器等引入的不确定度。

结合日常检测数据，首次采用欧洲标准化差值标准偏差的方法，对各不确定度分量进行评定。

当壁纸中甲醛含量范围为0.54～28.47 mg ／kg 时，测定结果在95%置信区间时的相对扩展不确定度为0.035 2(k =2)。

不确定度主要来源于样品移取过程中移液枪的使用、样品重复测定和标准曲线的拟合。

关键词　壁纸；甲醛；紫外可见分光光度法；相对扩展不确定度中图分类号：O657.3 文献标识码：A 文章编号：1008–6145(2021)01–0092–04Uncertainty assessment of formaldehyde in wallpaper by UV-vis spectrophotometryZhang Yanyan, Jia Hongli, Wang Ping, Wang Guangying, Cheng Jianwei, Zhao Yan, Yang Xiaolei,Wang Jianhui, Zeng Pan, Li Zhao(Qingdao Product Quality Supervision and Testing Research Center, Qingdao 266000, China)Abstract The concentration of formaldehyde in wallpaper was determined by UV-vis spectrophotometry and the uncertainty of measurement results was evaluated. According to the standard of GB 18585–2001 "Indoor Decorating and Refurbishing Materials-Limit of Harmful Substances of Wallpapers", the detection process of formaldehyde content in wallpaper was studied, and the source of uncertainty of the whole detection process was systematically analyzed. Sources of uncertainty include repeat measurement, sample extracts, standard solution preparation, fitting curve, and measuring instruments. Combined with the daily test data, the European standard deviation method was used for the first time to quantify the uncertainty components. Ander the 95% confidence interval, when the formaldehyde concentration in the wallpaper was from 0.54 mg ／kg to 28.47 mg ／kg, the relative extended uncertainty was 0.035 2 (k =2). Uncertainty factors are mainly derived from the use of pipette during sample removal and the repeated measurement of sample and the fitting of standard curveKeywords wallpaper; formaldehyde; UV-vis spectrophotometry; relative extended uncertainty壁纸是目前装饰装修材料中最为流行的建材产品之一，深受广大消费者的青睐［1］。

第１３卷㊀第１０期Ｖｏｌ．１３Ｎｏ．１０㊀㊀智㊀能㊀计㊀算㊀机㊀与㊀应㊀用ＩｎｔｅｌｌｉｇｅｎｔＣｏｍｐｕｔｅｒａｎｄＡｐｐｌｉｃａｔｉｏｎｓ㊀㊀２０２３年１０月㊀Ｏｃｔ．２０２３㊀㊀㊀㊀㊀㊀文章编号：２０９５－２１６３（２０２３）１０－００８３－０５中图分类号：ＴＰ３９１文献标志码：Ａ基于ＹＯＬＯｖ５的高分辨率遥感图像目标检测算法李在瑞，郑永果，东野长磊（山东科技大学计算机科学与工程学院，山东青岛２６６５９０）摘㊀要：针对高分辨率遥感图像中物体排布密集㊁尺度变化较大等特性，提出一种目标检测算法Ｒ－ＹＯＬＯｖ５㊂算法在ＹＯＬＯｖ５模型基础上首先将跨阶段局部扩张结构作用于主干网络，采用一种加强的特征提取方式，通过整合空洞卷积和密集连接，来缓解模型对密集分布目标的漏检问题；其次，在主干网络的瓶颈部分结合Ｔｒａｎｓｆｏｒｍｅｒ模块来增强特征的表达，突出目标区域；最后，引入多尺度特征融合模块，解决多尺度特征融合时存在的不一致性问题，以提高模型的检测效果㊂在公开的遥感图像检测数据集ＤＩＯＲ的实验结果表明，Ｒ－ＹＯＬＯｖ５算法平均精度均值（ｍＡＰ）达到８０．６％，具有良好的检测性能㊂关键词：遥感图像；目标检测；分布密集；ＹＯＬＯ；空洞卷积ＯｂｊｅｃｔｄｅｔｅｃｔｉｏｎａｌｇｏｒｉｔｈｍｆｏｒｈｉｇｈｒｅｓｏｌｕｔｉｏｎｒｅｍｏｔｅｓｅｎｓｉｎｇｉｍａｇｅｂａｓｅｄｏｎＹＯＬＯｖ５ＬＩＺａｉｒｕｉ，ＺＨＥＮＧＹｏｎｇｇｕｏ，ＤＯＮＧＹＥＣｈａｎｇｌｅｉ（ＣｏｌｌｅｇｅｏｆＣｏｍｐｕｔｅｒＳｃｉｅｎｃｅａｎｄＥｎｇｉｎｅｅｒｉｎｇ，ＳｈａｎｄｏｎｇＵｎｉｖｅｒｓｉｔｙｏｆＳｃｉｅｎｃｅａｎｄＴｅｃｈｎｏｌｏｇｙ，ＱｉｎｇｄａｏＳｈａｎｄｏｎｇ２６６５９０，Ｃｈｉｎａ）ʌＡｂｓｔｒａｃｔɔＡｉｍｉｎｇａｔｔｈｅｃｈａｒａｃｔｅｒｉｓｔｉｃｓｏｆｄｅｎｓｅｄｉｓｔｒｉｂｕｔｉｏｎａｎｄｌａｒｇｅｓｃａｌｅｖａｒｉａｔｉｏｎｏｆｏｂｊｅｃｔｓｉｎｈｉｇｈ－ｒｅｓｏｌｕｔｉｏｎｒｅｍｏｔｅｓｅｎｓｉｎｇｉｍａｇｅｓ，ａｎｏｂｊｅｃｔｄｅｔｅｃｔｉｏｎａｌｇｏｒｉｔｈｍＲ－ＹＯＬＯｖ５ｉｓｐｒｏｐｏｓｅｄ．ＯｎｔｈｅｂａｓｉｓｏｆＹＯＬＯｖ５ｍｏｄｅｌ，ｔｈｅａｌｇｏｒｉｔｈｍｆｉｒｓｔｌｙｉｎｔｒｏｄｕｃｅｓＣｒｏｓｓＳｔａｇｅＰａｒｔｉａｌＤｉｌａｔｅｄＮｅｔｗｏｒｋｉｎｔｈｅｂａｃｋｂｏｎｅｎｅｔｗｏｒｋ，ｗｈｉｃｈａｄｏｐｔｓａｎｅｎｈａｎｃｅｄｆｅａｔｕｒｅｅｘｔｒａｃｔｉｏｎｍｅｔｈｏｄｔｏａｌｌｅｖｉａｔｅｔｈｅｐｒｏｂｌｅｍｏｆｕｎｄｅｔｅｃｔｅｄｄｅｎｓｅｄｉｓｔｒｉｂｕｔｅｄｔａｒｇｅｔｓｂｙｉｎｔｅｇｒａｔｉｎｇｄｉｌａｔｅｄｃｏｎｖｏｌｕｔｉｏｎａｎｄｄｅｎｓｅｃｏｎｎｅｃｔｉｏｎ．Ｓｅｃｏｎｄｌｙ，ｉｎｔｈｅｂｏｔｔｌｅｎｅｃｋｐａｒｔｏｆｔｈｅｂａｃｋｂｏｎｅｎｅｔｗｏｒｋ，ｔｈｅＴｒａｎｓｆｏｒｍｅｒｍｏｄｕｌｅｉｓｃｏｍｂｉｎｅｄｔｏｅｎｈａｎｃｅｔｈｅｅｘｐｒｅｓｓｉｏｎｏｆｆｅａｔｕｒｅｓａｎｄｈｉｇｈｌｉｇｈｔｔｈｅｔａｒｇｅｔａｒｅａ．Ｆｉｎａｌｌｙ，ｍｕｌｔｉ－ｓｃａｌｅｆｅａｔｕｒｅｆｕｓｉｏｎｍｏｄｕｌｅｉｓｉｎｔｒｏｄｕｃｅｄｔｏｓｏｌｖｅｔｈｅｉｎｃｏｎｓｉｓｔｅｎｃｙｐｒｏｂｌｅｍｉｎｍｕｌｔｉ－ｓｃａｌｅｆｅａｔｕｒｅｆｕｓｉｏｎｔｏｉｍｐｒｏｖｅｔｈｅｄｅｔｅｃｔｉｏｎｅｆｆｅｃｔｏｆｔｈｅｍｏｄｅｌ．ＴｈｅｅｘｐｅｒｉｍｅｎｔａｌｒｅｓｕｌｔｓｏｎｐｕｂｌｉｃｒｅｍｏｔｅｓｅｎｓｉｎｇｉｍａｇｅｄｅｔｅｃｔｉｏｎｄａｔａｓｅｔＤＩＯＲｓｈｏｗｔｈａｔｔｈｅＭＡＰｏｆＲ－ＹＯＬＯｖ５ｒｅａｃｈｅｓ８０．６％，ｗｈｉｃｈｈａｓｇｏｏｄｄｅｔｅｃｔｉｏｎｐｅｒｆｏｒｍａｎｃｅ．ʌＫｅｙｗｏｒｄｓɔｒｅｍｏｔｅｓｅｎｓｉｎｇｉｍａｇｅ；ｏｂｊｅｃｔｄｅｔｅｃｔｉｏｎ；ｄｅｎｓｅｄｉｓｔｒｉｂｕｔｉｏｎ；ＹＯＬＯ；ｄｉｌａｔｅｄｃｏｎｖｏｌｕｔｉｏｎ作者简介：李在瑞（１９９８－），男，硕士研究生，主要研究方向：计算机视觉；郑永果（１９６３－），男，博士，教授，主要研究方向：虚拟现实与可视化㊁图像处理与模式识别；东野长磊（１９７８－），男，博士，副教授，主要研究方向：医学图像处理㊁计算机视觉㊂通讯作者：郑永果㊀㊀Ｅｍａｉｌ：ｓｋｄ９９１３１７＠ｓｄｕｓｔ．ｅｄｕ．ｃｎ收稿日期：２０２２－１１－０５０㊀引㊀言近些年，随着卫星及遥感技术的发展，遥感图像的目标检测在城市规划㊁灾情救援㊁车辆监控等各种实际应用中起到了至关重要的作用［１］㊂深度学习技术的迅速发展，使得目标检测有了重大突破，许多高性能的神经网络算法被提出［２］㊂目前，基于深度学习的目标检测算法可以大致分为二阶段算法和一阶段算法两类，二阶段算法专注于提升模型对目标的检测精度，一阶段方法则在追求精度的基础上又兼顾了检测速度㊂二阶段算法的经典模型是ＦａｓｔＲ－ＣＮＮ［３］，其使用ＲｅｇｉｏｎＰｒｏｐｏｓａｌＮｅｔｗｏｒｋ（ＲＰＮ）来选择对象的候选边界框，随后又进一步筛选出较为准确的目标区域㊂特征金字塔网络（ＦＰＮ）［４］使用类似金字塔的结构来学习不同尺度的特征㊂Ｔｒｉｄｅｎｔｎｅｔ［５］通过引入扩展卷积来改变大小最佳的感受野，并基于不同大小的感受野构造多分支结构，从而解决多尺度检测问题㊂一阶段模型中，ＳＳＤ［６］增加了多个卷积层，以获得多尺度特征图进行预测，并设计不同大小的先验边界框以更好地检测目标㊂ＹＯＬＯｖ４［７］采用了更为高效的ｃｓｐ－ｄａｒｋｎｅｔ作为主干网络并设计多尺度预测㊂ＴＰＨ－ＹＯＬＯｖ５［８］则将Ｔｒａｎｓｆｏｒｍｅｒ与网络相结合，增强模型提取特征的能力㊂以上算法虽然在识别自然图像时都表现出了良好的效果，但由于遥感图像存在背景复杂㊁目标尺度变化范围大㊁物体分布密集等检测难题［９］，通用目标检测算法对高分辨率遥感图像的检测具有很大的局限性［１０］㊂为解决上述问题，本文基于ＹＯＬＯｖ５框架，提出特征信息补充与加强以及多尺度融合的方法，以增强模型的检测能力㊂１㊀相关工作１．１㊀ＹＯＬＯｖ５模型随着ＹＯＬＯ系列网络的提出，其在各种视觉检测任务中展现了出色的性能㊂其中，ＹＯＬＯｖ５主干网络是由Ｆｏｃｕｓ模块㊁ＣＳＰ结构以及ＳＰＰ模块组合而成㊂Ｆｏｃｕｓ模型会对图片进行切片操作，在宽和高两个维度上每隔一个像素取一个值，从而使特征图的通道数变为原来的４倍，能够在最大程度减少信息损失的同时实现两倍下采样㊂ＹＯＬＯｖ５在ＣＳＰＮｅｔ［１１］的基础上重新设计ｃｓｐ结构，并在原本的ｄａｒｋｎｅｔ网络中大量插入该结构㊂ｓｐｐ模块对特征图做不同大小的池化操作，从而在原特征图的基础上融合不同感受野，丰富上下文信息［１２］㊂ＹＯＬＯｖ５在Ｎｉｃｋ部分结构参考了ＦＰＮ和ＰＡＮ㊂首先，设计自顶向下路径来融合网络中不同层次的特征，将包含丰富语义信息的深层特征向下传递与浅层结合，能够提高模型对多尺度目标的检测能力；后又增加自底向上的金字塔结构，把浅层特征映射到深层网络，补充检测目标的细节及空间信息，进一步提升模型的检测效果㊂同时，在ｎｉｃｋ部分应用ｃｓｐ２＿ｘ结构，使用Ｘ个卷积模块替代残差单元㊂Ｈｅａｄ部分则对图片进行预测与分类，ＹＯＬＯｖ５设计３种尺寸的特征图来检测大中小不同种类的目标，最后通过非极大值抑制来筛选预测框，实现检测过程㊂１．２㊀Ｔｒａｎｓｆｏｒｍｅｒ模块Ｔｒａｎｓｆｏｒｍｅｒ模块早先广泛应用于ＮＬＰ领域，通过自注意力机制来捕获序列元素之间的依赖关系，在可并行性和特征提取方面展现了出色的性能［１３］㊂近些年来，许多计算机视觉的学者开始将其作用于图像相关的研究上㊂Ｐａｒｍａｒ等人提出ＩｍａｇｅＴｒａｎｓｆｏｒｍｅｒ［１４］算法，基于Ｔｒａｎｓｆｏｒｍｅｒ解码器用于图像生成任务；随后ＶｉｓｉｏｎＴｒａｎｓｆｏｒｍｅｒ［１５］被提出，并首次在大型图像数据集上展现出超越卷积网络的性能，在图像分类方面具有较强的泛化能力；ＳｗｉｎＴｒａｎｓｆｏｒｍｅｒ［１６］则采用移动窗口的机制来计算注意力，有效解决了传统Ｔｒａｎｓｆｏｒｍｅｒ模块中计算复杂度较高的问题，并通过不同窗口之间的特征交互提取到更为丰富的语义信息㊂Ｔｒａｎｓｆｏｒｍｅｒ由编码器和解码器两部分组成，基本原理是通过将图片展开成一维，得到图像特征张量，输入到编码器部分使用多头自注意力学习目标特征，增强图像中目标的语义信息，再利用解码器与解码器协同训练，学习注意力规律来强化目标和特征之间的关联关系，进而提升检测效果㊂２㊀Ｒ－ＹＯＬＯｖ５遥感图像目标检测算法Ｒ－ＹＯＬＯｖ５目标检测算法结构如图１所示㊂首先，在ＹＯＬＯｖ５的主干网络ＣＳＰＤａｒｋＮｅｔ中使用跨阶段局部扩张结构，替代原本的跨阶段局部网络结构；其次，在主干网络的输出特征图瓶颈部分结合Ｔｒａｎｓｆｏｒｍｅｒ模块中的编码器；最后，在原本的Ｎｉｃｋ部分嵌入多尺度特征融合模块㊂S P PT R -B o t t l e n e c k C S P D 1_3C S P 1_1C o n vF o c u sT R -B o t t l e n e c k C S P D 1_3S P PC S PD 2_1C o n c a tC o n c a tC o n vC S PD 2_1C o n c a tC S PD 2_1C o n vT R -B o t t l e n e c kC S PD 2_1C S P D 2_1C o n c a tM S FC a tM a x p o o lM a x p o o l M a x p o o lP r e d i t i o nM S FC o n vC o n v C o n vC a tS o f t M a xC o n v C o n vC a tC a tC o n vC o n v2*C o n v6?D i l a t e d C o n vC S PD 1_XC S PD 2_X X *C o n v6?D i l a t e dC o n vX 个残差单元图１㊀Ｒ－ＹＯＬＯｖ５算法结构Ｆｉｇ．１㊀Ｒ－ＹＯＬＯｖ５ａｌｇｏｒｉｔｈｍｓｔｒｕｃｔｕｒｅ４８智㊀能㊀计㊀算㊀机㊀与㊀应㊀用㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀第１３卷㊀２．１㊀跨阶段局部扩张结构跨阶段局部网络结构（ＣｒｏｓｓＳｔａｇｅＰａｒｔｉａｌＳｔｒｕｃｔｕｒｅ，ＣＳＰ）被大量应用到ＹＯＬＯｖ４的主干网络，ＹＯＬＯｖ５又在ｖ４的基础上将其与ｎｉｃｋ部分结合㊂ＣＳＰ结构包括两个分支：一是将输入特征图进行Ｘ个残差单元的卷积操作，另一部分进行简单的３∗３卷积计算特征后，与上一分支结合㊂ＣＳＰ结构能够增强网络的特征提取能力，使模型获取到更为丰富的语义信息㊂针对遥感图像中检测目标尺度变化较大，物体分布密集的特性，对ＣＳＰ结构进行改进，提出跨阶段局部扩张结构（ＣｒｏｓｓＳｔａｇｅＰａｒｔｉａｌＤｉｌａｔｅｄＳｔｒｕｃｔｕｒｅ，ＣＳＰＤ），如图２所示㊂首先，保持残差单元分支不变，在另一分支中使用６个连续的扩张卷积，扩张率分别为３㊁６㊁１２㊁１８㊁２４，来获取同一特征图的不同感受野，从而覆盖遥感图像中各种不同尺度的检测对象㊂其次，当图像中目标分布较为紧密时，使用扩张卷积会丢失特征信息，为了避免检测对象的漏检现象，在连续的６个扩张卷积基础上采用密集连接结构，将原特征图与每层的卷积分别做逐个元素的加操作，从而加强特征的传播，丰富语义信息㊂X 个残差单元C o n c a tD =3D =6D =12D =18D=24图２㊀跨阶段局部扩张模块结构图Ｆｉｇ．２㊀ＣｒｏｓｓＳｔａｇｅＰａｒｔｉａｌＤｉｌａｔｅｄｍｏｄｕｌｅ２．２㊀瓶颈Ｔｒａｎｓｆｏｒｍｅｒ结构ＹＯＬＯｖ５主干网络分别输出３个不同层次大小的特征图，作为后续多尺度特征融合部分的输入㊂将主干网络中负责输出特征图的瓶颈（Ｂｏｔｔｌｅｎｅｃｋ）部分与Ｔｒａｎｓｆｏｒｍｅｒ模块中的编码器相结合（如图３所示），提出瓶颈Ｔｒａｎｓｆｏｒｍｅｒ结构（ＴＲ－Ｂｏｔｔｌｅｎｅｃｋ），提高模型对语义信息的提取能力，丰富图像全局信息，抑制背景对目标识别的影响㊂首先，将图片做切分并降低维度，即将原本Ｈ∗Ｗ∗Ｃ的图像变为Ｎ∗（Ｐ２∗Ｃ）的Ｔｏｋｅｎｓ，其中Ｎ＝ＨＷ∗Ｐ２；随后输入Ｅｎｃｏｄｅｒ中的多头注意力机制，进一步做特征提取，如式（１）所示：ＡｔｔｅｎＱ，Ｋ，Ｖ()＝ｓｏｆｔｍａｘＱＫＴ㊀ｄｋæèçöø÷Ｖ（１）式中：Ｑ㊁Ｋ㊁Ｖ分别为输入多头注意力的查询向量㊁键向量㊁值向量，ｄｋ代表特征维度㊂将查询向量与键向量相乘后，经过ｓｏｆｔｍａｘ激活函数并归一化处理，再与Ｖ相乘加权，得到输出结果㊂最后输入由两个全连接层及激活函数组成的ＭＬＰ（前馈神经网络）得到整个Ｔｒａｎｓｆｏｒｍｅｒ模块的输出特征，并与Ｂｏｔｔｌｅｎｃｋ结构的特征信息结合㊂T R -B o t t l e n e c kM u l t i -H e a dA t t e n t i o nC o n v C o n v C o n vC o n vC o n vB nR e L U*2C o n c a tT r a n s f o r m e r M L P图３㊀瓶颈Ｔｒａｎｓｆｏｒｍｅｒ模块结构图Ｆｉｇ．３㊀Ｔｒａｎｓｆｏｒｍｅｒｂｏｔｔｌｅｎｅｃｋｍｏｄｕｌｅ２．３㊀多尺度特征融合模块ＹＯＬＯｖ５输出的３种尺寸的特征图，分别对应大中小不同的检测对象，高层语义信息中检测大目标，低层语义信息中检测小目标，而遥感图像中往往既有大目标又有小目标㊂特征融合时，由于不同层间特征的不一致性，将会影响最后的检测结果㊂为了缓解上述问题，更好的让网络利用高低层语义信息，在ｎｉｃｋ部分的最后，嵌入多尺度特征融合模块（ＭｕｌｔｉＳｃａｌｅＦｅａｔｕｒｅＦｕｓｉｏｎＭｏｄｕｌｅ，ＭＳＦ），如图４所示㊂S o f t M a x压缩压缩压缩图４㊀多尺度特征融合模块结构图Ｆｉｇ．４㊀Ｍｕｌｔｉ－ｓｃａｌｅｆｅａｔｕｒｅｆｕｓｉｏｎｍｏｄｕｌｅ㊀㊀首先将３种尺寸的特征图进行采样操作，调整到同一尺寸；再根据通道维度整合并接入ＳｏｆｔＭａｘ函数生成权重参数；最后３层特征分别乘上各自的权重参数，得到融合后的特征，表达如式（２）所示：ｆ＝ð３ｉ＝１ＳｏｆｔＭａｘ（ｃａｔ（ｘ１ｘ２ｘ３）） ｘｉ（２）式中：ｘ１㊁ｘ２㊁ｘ３分别为３种尺寸的特征图，ｃａｔ表示对特征图做通道维度的整合， 表示点乘操作，ｆ则为最终的输出特征㊂５８第１０期李在瑞，等：基于ｙｏｌｏｖ５的高分辨率遥感图像目标检测算法３㊀实验３．１㊀实验环境与数据集实验在ｌｉｎｕｘ系统下进行，所用ＧＰＵ为ＴｅｓｌａＰ１００，显存１６Ｇ，深度学习框架为ｐｙｔｏｒｃｈ㊂实验所用遥感数据集为ＤＩＯＲ，其中包括２３４６３张图像，训练与测试各取一半的样本㊂３．２㊀评价指标实验采用平均精度均值（ｍＡＰ）㊁平均精确率（ＡＰ）作为评估指标，ＡＰ和ｍＡＰ是可以反映多类别目标全局检测精度的指标在文献中被广泛用于评估多类别目标检测性能表达如式（２）㊁（３）所示：ＡＰ＝ʏ１０ｐＲ()ｄＲ（３）ｍＡＰ＝１ＮðｉＡＰｉ（４）㊀㊀其中，平均精度ＡＰ表示的是计算单类目标Ｐ－Ｒ曲线下面积的结果，ｐ为精确率，Ｒ为召回率；而ｍＡＰ是所有类别ＡＰ的平均值；Ｎ为检测目标的类别总数；ＡＰｉ表示第ｉ个类别的平均检测精度㊂３．３㊀算法流程如图５所示，Ｒ－ＹＯＬＯｖ５算法首先对输入的遥感图像进行预处理，扩展图像数据；其次，根据模型配置文件搭建网络结构，读取训练参数，并根据训练结果更新网络参数；最后，加载训练权重与测试数据集，输出模型的预测图像㊂搭建网络读取参数输出结果更新参数训练模型训练集测试集数据预处理归一化数据扩充遥感图像图５㊀Ｒ－ＹＯＬＯｖ５算法流程图Ｆｉｇ．５㊀Ｒ－ＹＯＬＯｖ５ａｌｇｏｒｉｔｈｍｆｌｏｗｃｈａｒｔ３．４㊀实验结果表１为本文算法Ｒ－ＹＯＬＯｖ５与不同目标检测模型在ＤＩＯＲ数据集下的实验结果㊂其中包括一阶段模型Ｆａｓｔｅｒ－ＲＣＮＮ，以ＳＳＤ㊁ＲｅｔｉｎａＮｅｔ㊁ＹＯＬＯｖ４为代表的二阶段模型，及无锚方法ＹＯＬＯＸ㊂表１㊀ＤＩＯＲ数据集下对比试验Ｔａｂ．１㊀ＲｅｓｕｌｔｓｏｎＤｉｏｒｄａｔａｓｅｔ％ＭＥＴＨＯＤＦａｓｔｅｒ－ＲＣＮＮＳＳＤＲｅｔｉｎａＮｅｔＹＯＬＯｖ４ＹＯＬＯＸＲ－ＹＯＬＯｖ５Ｅｘｐｒｅｓｓｗａｙｓｅｒｖｉｃｅａｒｅａ６５６４９０８９８０９３Ｂａｓｋｅｔｂａｌｌｃｏｕｒｔ７１７６９０８７８９９２Ｔｅｎｎｉｓｃｏｕｒｔ７７７６８７８８９０９２ｇｏｌｆｆｉｅｌｄ７０６５８５７４７２８６Ｇｒｏｕｎｄｔｒａｃｋｆｉｅｌｄ６２６９８３８２８１８８Ｓｔａｄｉｕｍ９４６１８１７０７４８０Ｃｈｉｍｎｅｙ８９６６８１８０７６８２Ａｉｒｐｏｒｔ６８７２７９８０７１９２Ｄａｍ５９５７７５７０６１８１Ｂａｓｅｂａｌｌｆｉｅｌｄ９２７２７４８５８４８１Ｗｉｎｄｍｉｌｌ４４６６７０８３８９９２Ａｉｒｐｌａｎｅ９１６０６８７３８５８４Ｔｒａｉｎｓｔａｔｉｏｎ４０５５６１６３４８７５Ｅｘｐｒｅｓｓｗａｙｔｏｌｌｓｔａｔｉｏｎ５５５３５９７１７１８３Ｈａｒｂｏｒ５４４９５９６３５２６７Ｏｖｅｒｐａｓｓ５１４８５７６２６１６６Ｓｈｉｐ２１５９４７８５８８９１ｂｒｉｄｇｅ２２３０３７４４４４５５Ｓｔｏｒａｇｅｔａｎｋ７３４７３４６３７０７６Ｖｅｈｉｃｌｅ３０２７２１４４４９５８ＭＡＰ６１．５８５８６６．９２７２．６９７１．７８０．６㊀㊀由表１可知，Ｒ－ＹＯＬＯｖ５对飞机㊁机场㊁船㊁桥㊁车辆等密集分布㊁大小尺度不一目标的精度均有不同程度的提高，具有良好的表现㊂图６所示为Ｒ－ＹＯＬＯｖ５对密集分布㊁大小尺度不一目标的效果图㊂这两种情况在检测过程中都较易对目标错检或漏检，模型识别的难度较大㊂如图６８智㊀能㊀计㊀算㊀机㊀与㊀应㊀用㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀㊀第１３卷㊀６（ａ）㊁（ｂ）中飞机与油罐的分布较为密集，模型对此类目标能够较为全面的做出识别；图６（ｃ）㊁（ｄ）中车辆与桥梁㊁棒球场与网球场等各类物体的尺度变化给模型带来了检测难题，结果表明，Ｒ－ＹＯＬＯｖ５可以较为准确的检测出目标对象㊂（a ）飞机场（b ）油罐场（c ）车辆与桥梁（d ）棒球场与网球场图６㊀Ｒ－ＹＯＬＯｖ５检测结果Ｆｉｇ．６㊀Ｒ－ＹＯＬＯｖ５ｄｅｔｅｃｔｉｏｎｒｅｓｕｌｔ４㊀结束语基于高分辨率遥感图像存在检测对象密集度高㊁大小不一等问题㊂本文提出Ｒ－ＹＯＬＯｖ５算法，通过扩大感受野和增强特征信息以及改善特征融合来提高模型对密集物体以及多尺度目标的检测精度㊂实验表明，本文提出的目标检测算法在遥感数据集上具有较好的识别能力㊂参考文献［１］ＳＣＨＩＬＬＩＮＧＨ，ｄＵＬＡＴＯＶＤ，ＮＩＥＳＳＮＥＲＲ，ｅｔａｌ．Ｄｅｔｅｃｔｉｏｎｏｆｖｅｈｉｃｌｅｓｉｎｍｕｌｔｉｓｅｎｓｏｒｄａｔａｖｉａｍｕｌｔｉｂｒａｎｃｈｃｏｎｖｏｌｕｔｉｏｎａｌｎｅｕｒａｌｎｅｔｗｏｒｋｓ［Ｊ］．ＩＥＥＥＥＪｏｕｒｎａｌｏｆＳｅｌｅｃｔｅｄＴｏｐｉｃｓｉｎＡｐｐｌｉｅｄＥａｒｔｈＯｂｓｅｒｖａｔｉｏｎｓａｎｄＲｅｍｏｔｅＳｅｎｓｉｎｇ，２０１８，１１（１）：４２９９－４３１６．［２］ＣＨＥＮＪ，ＹＵＥＡ，ＷＡＮＧＣ，ｅｔａｌ．Ｗｉｎｄｔｕｒｂｉｎｅｅｘｔｒａｃｔｉｏｎｆｒｏｍｈｉｇｈｓｐａｔｉａｌｒｅｓｏｌｕｔｉｏｎｒｅｍｏｔｅｓｅｎｓｉｎｇｉｍａｇｅｓｂａｓｅｄｏｎｓａｌｉｅｎｃｙｄｅｔｅｃｔｉｏｎ［Ｊ］．ＪｏｕｒｎａｌｏｆＡｐｐｌｉｅｄＲｅｍｏｔｅＳｅｎｓｉｎｇ，２０１８，１２（１）：０１６０４１．［３］ＧＩＲＳＨＩＣＫＲ．Ｆａｓｔｒ－ｃｎｎ［Ｃ］／／ＰｒｏｃｅｅｄｉｎｇｓｏｆｔｈｅＩＥＥＥｉｎｔｅｒｎａｔｉｏｎａｌｃｏｎｆｅｒｅｎｃｅｏｎｃｏｍｐｕｔｅｒｖｉｓｉｏｎ．２０１５：１４４０－１４４８．［４］ＬＩＮＴＹ，ＤＯＬＬ ＲＰ，ＧＩＲＳＨＩＣＫＲ，ｅｔａｌ．Ｆｅａｔｕｒｅｐｙｒａｍｉｄｎｅｔｗｏｒｋｓｆｏｒｏｂｊｅｃｔｄｅｔｅｃｔｉｏｎ［Ｃ］／／ＰｒｏｃｅｅｄｉｎｇｓｏｆｔｈｅＩＥＥＥｃｏｎｆｅｒｅｎｃｅｏｎｃｏｍｐｕｔｅｒｖｉｓｉｏｎａｎｄｐａｔｔｅｒｎｒｅｃｏｇｎｉｔｉｏｎ．２０１７：２１１７－２１２５．［５］ＬＩＹ，ＣＨＥＮＹ，ＷＡＮＧＮ，ｅｔａｌ．Ｓｃａｌｅ－ａｗａｒｅｔｒｉｄｅｎｔｎｅｔｗｏｒｋｓｆｏｒｏｂｊｅｃｔｄｅｔｅｃｔｉｏｎ［Ｃ］／／ＰｒｏｃｅｅｄｉｎｇｓｏｆｔｈｅＩＥＥＥ／ＣＶＦｉｎｔｅｒｎａｔｉｏｎａｌｃｏｎｆｅｒｅｎｃｅｏｎｃｏｍｐｕｔｅｒｖｉｓｉｏｎ．２０１９：６０５４－６０６３．［６］ＬＩＵＷ，ＡＮＧＵＥＬＯＶＤ，ＥＲＨＡＮＤ，ｅｔａｌ．Ｓｓｄ：Ｓｉｎｇｌｅｓｈｏｔｍｕｌｔｉｂｏｘｄｅｔｅｃｔｏｒ［Ｃ］／／ＣｏｍｐｕｔｅｒＶｉｓｉｏｎ－ＥＣＣＶ２０１６：１４ｔｈＥｕｒｏｐｅａｎＣｏｎｆｅｒｅｎｃｅ，Ａｍｓｔｅｒｄａｍ，ＴｈｅＮｅｔｈｅｒｌａｎｄｓ，Ｏｃｔｏｂｅｒ１１－１４，２０１６，Ｐｒｏｃｅｅｄｉｎｇｓ，ＰａｒｔＩ１４．ＳｐｒｉｎｇｅｒＩｎｔｅｒｎａｔｉｏｎａｌＰｕｂｌｉｓｈｉｎｇ，２０１６：２１－３７．［７］ＢＯＣＨＫＯＶＳＫＩＹＡ，ＷＡＮＧＣＹ，ＬＩＡＯＨＹＭ．Ｙｏｌｏｖ４：Ｏｐｔｉｍａｌｓｐｅｅｄａｎｄａｃｃｕｒａｃｙｏｆｏｂｊｅｃｔｄｅｔｅｃｔｉｏｎ［Ｊ］．ａｒＸｉｖｐｒｅｐｒｉｎｔａｒＸｉｖ：２００４．１０９３４，２０２０．［８］ＺＨＵＸ，ＬＹＵＳ，ＷＡＮＧＸ，ｅｔａｌ．ＴＰＨ－ＹＯＬＯｖ５：ＩｍｐｒｏｖｅｄＹＯＬＯｖ５ｂａｓｅｄｏｎｔｒａｎｓｆｏｒｍｅｒｐｒｅｄｉｃｔｉｏｎｈｅａｄｆｏｒｏｂｊｅｃｔｄｅｔｅｃｔｉｏｎｏｎｄｒｏｎｅ－ｃａｐｔｕｒｅｄｓｃｅｎａｒｉｏｓ［Ｃ］／／ＰｒｏｃｅｅｄｉｎｇｓｏｆｔｈｅＩＥＥＥ／ＣＶＦｉｎｔｅｒｎａｔｉｏｎａｌｃｏｎｆｅｒｅｎｃｅｏｎｃｏｍｐｕｔｅｒｖｉｓｉｏｎ．２０２１：２７７８．［９］ＺＨＡＮＧＧ，ＬＵＳ，ＺＨＡＮＧＷ．ＣＡＤ－Ｎｅｔ：Ａｃｏｎｔｅｘｔ０ａｗａｒｅｄｅｔｅｃｔｉｏｎｎｅｔｗｏｒｋｆｏｒｏｂｊｅｃｔｓｉｎｒｅｍｏｔｅｓｅｎｓｉｎｇｉｍａｇｅｒｙ［Ｊ］．ＩＥＥＥＴｒａｎｓａｃｔｉｏｎｓｏｎＧｅｏｓｃｉｅｎｃｅａｎｄＲｅｍｏｔｅＳｅｎｓｉｎｇ，２０１９，５７（１２）：１００１５－１００２４．［１０］ＺＨＥＮＧＺ，ＬＥＩＬ，ＳＵＮＨ，ｅｔａｌ．Ａｒｅｖｉｅｗｏｆｒｅｍｏｔｅｓｅｎｓｉｎｇｉｍａｇｅｏｂｊｅｃｔｄｅｔｅｃｔｉｏｎａｌｇｏｒｉｔｈｍｓｂａｓｅｄｏｎｄｅｅｐｌｅａｒｎｉｎｇ［Ｃ］／／２０２０ＩＥＥＥ５ｔｈＩｎｔｅｒｎａｔｉｏｎａｌＣｏｎｆｅｒｅｎｃｅｏｎＩｍａｇｅ，ＶｉｓｉｏｎａｎｄＣｏｍｐｕｔｉｎｇ（ＩＣＩＶＣ）．ＩＥＥＥ，２０２０：３４－４３．［１１］ＷＡＮＧＣＹ，ＬＩＡＯＨＹＭ，ＷＵＹＨ，ｅｔａｌ．ＣＳＰＮｅｔ：ＡｎｅｗｂａｃｋｂｏｎｅｔｈａｔｃａｎｅｎｈａｎｃｅｌｅａｒｎｉｎｇｃａｐａｂｉｌｉｔｙｏｆＣＮＮ［Ｃ］／／ＰｒｏｃｅｅｄｉｎｇｓｏｆｔｈｅＩＥＥＥ／ＣＶＦｃｏｎｆｅｒｅｎｃｅｏｎｃｏｍｐｕｔｅｒｖｉｓｉｏｎａｎｄｐａｔｔｅｒｎｒｅｃｏｇｎｉｔｉｏｎｗｏｒｋｓｈｏｐｓ．２０２０：３９０－３９１．［１２］ＣＡＯＬ，ＺＨＡＮＧＸ，ＷＡＮＧＺ，ｅｔａｌ．Ｍｕｌｔｉａｎｇｌｅｒｏｔａｔｉｏｎｏｂｊｅｃｔｄｅｔｅｃｔｉｏｎｆｏｒｒｅｍｏｔｅｓｅｎｓｉｎｇｉｍａｇｅｂａｓｅｄｏｎｍｏｄｉｆｉｅｄｆｅａｔｕｒｅｐｙｒａｍｉｄｎｅｔｗｏｒｋｓ［Ｊ］．ＩｎｔｅｒｎａｔｉｏｎａｌＪｏｕｒｎａｌｏｆＲｅｍｏｔｅＳｅｎｓｉｎｇ，２０２１，４２（１４）：５２５３－５２７６．［１３］ＷＡＮＧＣ，ＢＡＩＸ，ＷＡＮＧＳ，ｅｔａｌ．ＭｕｌｔｉｓｃａｌｅＶｉｓｕａｌａｔｔｅｎｔｉｏｎｎｅｔｗｏｒｋｓｆｏｒｏｂｊｅｃｔｄｅｔｅｃｔｉｏｎｉｎＶＨＲｒｅｍｏｔｅｓｅｎｓｉｎｇｉｍａｇｅｓ［Ｊ］．ＩＥＥＥＧｅｏｓｃｉｅｎｃｅａｎｄＲｅｍｏｔｅＳｅｎｓｉｎｇＬｅｔｔｅｒｓ，２０１８，１６（２）：３１０－３１４．［１４］ＰＡＲＭＡＲＮ，ＶＡＳＷＡＮＩＡ，ＵＳＺＫＯＲＥＩＴＪ，ｅｔａｌ．Ｉｍａｇｅｔｒａｎｓｆｏｒｍｅｒ［Ｃ］／／Ｉｎｔｅｒｎａｔｉｏｎａｌｃｏｎｆｅｒｅｎｃｅｏｎｍａｃｈｉｎｅｌｅａｒｎｉｎｇ．ＰＭＬＲ，２０１８：４０５５－４０６４．［１５］ＤＯＳＯＶＩＴＳＫＩＹＡ，ＢＥＹＥＲＬ，ＫＯＬＥＳＮＩＫＯＶＡ，ｅｔａｌ．Ａｎｉｍａｇｅｉｓｗｏｒｔｈ１６ˑ１６ｗｏｒｄｓ：Ｔｒａｎｓｆｏｒｍｅｒｓｆｏｒｉｍａｇｅｒｅｃｏｇｎｉｔｉｏｎａｔｓｃａｌｅ［Ｊ］．ａｒＸｉｖｐｒｅｐｒｉｎｔａｒＸｉｖ：２０１０．１１９２９，２０２０．［１６］ＬＩＵＺ，ＬＩＮＹ，ＣＡＯＹ，ｅｔａｌ．Ｓｗｉｎｔｒａｎｓｆｏｒｍｅｒ：Ｈｉｅｒａｒｃｈｉｃａｌｖｉｓｉｏｎｔｒａｎｓｆｏｒｍｅｒｕｓｉｎｇｓｈｉｆｔｅｄｗｉｎｄｏｗｓ［Ｃ］／／ＰｒｏｃｅｅｄｉｎｇｓｏｆｔｈｅＩＥＥＥ／ＣＶＦｉｎｔｅｒｎａｔｉｏｎａｌｃｏｎｆｅｒｅｎｃｅｏｎｃｏｍｐｕｔｅｒｖｉｓｉｏｎ．２０２１：１００１２－１００２２．７８第１０期李在瑞，等：基于ｙｏｌｏｖ５的高分辨率遥感图像目标检测算法。

WE-EF-303-03: A New Aperture-Based Imaging System for Prompt-Gamma Range Verificationof Proton Beam Therapy关于质子束照射法快速伽马范围验证, 1种基于新式孔径的图像化系统本文章为德国慕尼黑质子治疗中心RPTC专项质子照射法临床效果研究, 目的是为了探索质子束照射法快速伽马范围验证的1种基于孔径的新式图像化系统Abstract摘要Purpose:目的就高能伽马(γ)射线来说, 本研究的目的是为了开发与描述1种新颖基于孔径的图像化系统.通过快速γ射线探测的方式, 这种校准系统将可以为质子束范围及布拉格峰剂量的验证方面提供2D的图像化能力.Methods:方法本研究设计制造了1种多刀刃狭缝准直器, 并通过模拟和实验性测量值的方式将其描述出来. 本研究在采用基于TOPAS Geant4蒙特卡罗软件包的手段下, 将20×20×7.5 cm(3)钨准直器与伴随的LSO闪烁探测器模拟出来.迭代重建方法在本研究中被结合了点响应函数以描述该系统的图像化性能.开始时, 实验上看该系统的反应被描述良好, 采用了产生自Th-228的2.6MeV幅度γ射线.Results:结果模拟和实验的结果预示出, 这种校准系统在能量范围内就有关快速γ剂量的验证提供了2D 的图像化能力.在目前设置内, 通过准直器来探索13cm距离, 点源的图像重建在成像平面的X与γ方向中导致了约4mm的空间分辨率. 定位点源的准确性达到小于1mm的结果.Conclusions:结论在1件更传统位置敏感的LSO闪烁探测器前, 本研究通过模拟与测量值描述了1种新颖多刀刃的狭缝准直器.该型多狭缝的图案被设计来增加探测的有效性, 并且在2D方面提供了空间信息, 这是1种对单狭缝准直器设计的改进之处.该准直器的厚度与密度将可以允许这种探测系统在带有高γ流量的环境内来执行任务, 同时最大限度地为1mm顺序提供了峰值的测定准确度.。

a r Xi v:as tr o-ph/97528v16May1997Limits on Expanding Relativistic Shells from Gamma-Ray Burst Temporal Structure E.E.FENIMORE Los Alamos National Laboratory,MS D436,Los Alamos,NM 87544,USA We calculate the expected envelope of emission for relativistic shells under the assumption of local spherical symmetry.Gamma-Ray Burst envelopes rarely con-form to the expected shape,which has a fast rise and a smooth,slower decay.Furthermore,the duration of the decay phase is related to the time the shell ex-pands before converting its energy to gamma rays.From this,one can estimate the energy required for the shell to sweep up the ISM.The energy greatly exceeds 1053erg unless the bulk Lorentz factor is less than 75.This puts extreme limits on the “external”shock models.However,the alternative,“internal”shocks from a central engine,has one large problem:the entire long complex time history lasting hundreds of seconds must be postulated at the central site.The temporal structure of long complex Gamma-Ray Bursts (GRBs)presents a myriad of problems for models that involve a single central release of energy,as in many cosmological scenarios.Bursts with 50peaks within 100seconds are not uncommon,and there is the recent report 1of a burst which might have lasted from 103to 105seconds.In Fenimore,Madras,&Nayakshin 2(hereafter FMN),we used kinematic limits and the observed temporal structure of GRBs to estimate the characteristics of the gamma-ray producing regions.The bulk Lorentz factor of the shell,Γ,must be 102to 103in order to avoid photon-photon attenuation 3,4.Since the emitting surface is in relativistic motion,the simple rule that the size is limited to ∼c ∆T does not apply.The high Γfactor implies that visible shells are moving directly towards the observer:if the material of the shell is a narrow cone,it is unlikely that the observer wouldbe within the radiation beam yet outside the cone of material (see FMN).Surprisingly,the curvature of the shell within Γ−1is just as important in determining the envelope of emission as the overall expansion.This is under-stood by distinguishing the arrival time of the photons at the detector from the detector’s rest frame time.We denote the former as T ,and the latter as t .Assume the shell expands at velocity v and emits for time t .Because the emitting surface keeps up with the emitted photons,the photons will arrive at the detector within time T =(c −v )t/c ≈t/(2Γ2).In contrast,the curva-ture of the shell causes photons emitted from the material at angle θ=Γ−1to arrive after the photons emitted on axis by T =vt (1−cos θ)≈t/(2Γ2).Thus,both the overall expansion (which might last 107sec)and the delays1caused by the curvature spread the observed signal over arrival times by about t/(2Γ2).Envelopes should,therefore,be estimated under the assumption of “local spherical symmetry”:local because onlyθ∼Γ−1can contribute,sym-metric because the material is seen head on,and spherical because curvature effects are important.One can calculate the expected envelope of emission from an expanding shell.Let P(θ,φ,R)give the rate of gamma-ray production for the shell as a function of spherical coordinates.Motivated by the“external shock”models5, we assume a single shell,R=vt,which expands for a time(t0)in a photon quiet phase and then emits from t0to t max(i.e.,P(θ,φ,R)=P0from R=vt0 to R=vt max,and zero otherwise).In terms of arrival time,the on-axis emission will arrive between T0=t0/(2Γ2)and T max=t max/(2Γ2).However, because the curvature is important,off-axis photons will be delayed,and most emission will arrive much later.The expected envelope,V(T),is:V(T)=0if T<T0(1a)=KP0Tα+3−Tα+3Tα+1if T>T max(1c)whereαis a typical number spectral index(∼1.5)and K is a constant.This envelope is similar to a“FRED”(fast rise,exponential decay)where the fast rise depends mostly on the duration of the photon active phase(T max−T0)and the slow,power law decay depends mostly on the duration of the pho-ton quiet phase.The decay phase is due to photons delayed by the curvature.Often,GRBs do not have a FRED-like shape,implying that something must break the local spherical symmetry.Perhaps P(θ,φ,R)is patchy on angular scales smaller thanΓ−1,with each patch contributing an observed peak.If so,we define the“filling factor”,f,to be the ratio of the observed emission to what we would expect under local spherical symmetry(see Eq.32 in FMN):f=P(θ,φ,t)(1−βcosθ)−3dAFrom Eq.1,wefind that the half-width of a GRB,∼T dur/2,is∼T0/5.Thus the shell expands to about R∼5Γ2T dur before becoming ac-tive.In previous work5,the photon quiet phase was estimated from E0= (Ω/4π)R3decρISM(m p c2)Γ2where E0is the energy required to sweep up the ISM with densityρISM,m p is the mass of a proton,Ωis the total angular size of the shell,and R dec is the radius of the photon quiet phase where the shell decelerates and begins to convert its energy to gamma-rays.(Note that one cannot solve E0for R dec with an assumedΓbecause R is related toΓthrough the curvature effects.)Using R=5Γ2T dur,wefind that E0is an extremely strong function ofΓ:E0∼1032Γ8T3durΩρISM erg.Unless E0is much larger than1053erg,Γis quite small(∼75)for bursts with T dur∼100s.Piran6has suggested that thefilling factor is∼1/N,where N is the number of peaks in a burst,and that thisfilling factor is so small that it rules out single relativistic shells in favor of central engines.However,it is possible to create many peaks and have a largefilling factor(as in Eq.2)by allowing for variations in P(θ,φ,R)(work in progress).Thus,we believe it is too premature to“rule out”single relativistic shells.Also,there are other ways to overcome inefficiencies.For example,Ωmight be small.Shaviv7has suggested that a single shell sweeps over a cluster of stars with each star contributing a peak to the time history.However,in such a scenario,T0is effectively zero so the envelope should have a rise that scales as T2(cf.Eq.1),which is not often seen.In addition,the Shaviv model requires Γ∼103,so the energy to sweep up the ISM is extremely large:1062ρISMΩ. Globular clusters will have smallρISM,but not small enough.Other issues related to the time history and emission process have been raised by Dermer8.We conclude that GRBs do not show the signature of a single relativistic shell,and models must,therefore,explain how local spherical symmetry is broken enough to produce the chaotic time histories.Note added for astro-ph:In Fenimore,Madras,&Nayakshin,equation(1) was incorrectly dervied and that was repeated in the manuscript of this paper submitted to the proceedings.The error was corrected in Fenimore&Sumner (Proc of All-Sky X-ray Observations in the Next Decade Workshop)and here. The difference in the equations does not affect our conclusions.1.V.Connaughton,In Preparation.2.E.E.Fenimore,C.D.Madras,and S.Nayakshin,Ap.J.473,998(1996,astro-ph/9607163).3.M.G.Baring,Ap.J.418,391(1993).4.S.Nayakshin and E.E.Fenimore,to be submitted,Ap.J..5.P.Meszaros and M.Rees,Ap.J.405,278(1993).6.T.Piran,These Proceedings and R.Sari and T.Piran,Preprint.37.N.Shaviv,These Proceedings and N.Shaviv and A.Dar,Mon.Not.Royal.Astron.Soc.269,1112(1995).8.C.Dermer,submitted to Ap.J..4。

a r X i v :ast r o -p h /0601238v 2 12 J a n 2006Astronomy &Astrophysics manuscript no.2913vb February 5,2008(DOI:will be inserted by hand later)A microquasar model applied to unidentified gamma-ray sourcesV.Bosch-Ramon 1,J.M.Paredes 1,G.E.Romero 2,3,⋆⋆,and D.F.Torres 41Departament d’Astronomia i Meteorologia,Universitat de Barcelona,Av.Diagonal 647,E-08028Barcelona,Spain;vbosch@am.ub.es,jmparedes@.2Instituto Argentino de Radioastronom ´ıa, C.C.5,(1894)Villa Elisa,Buenos Aires,Argentina;romero@.ar.3Facultad de Ciencias Astron´o micas y Geof ´ısicas,UNLP,Paseo del Bosque,1900La Plata,Argentina.4Lawrence Livermore National Laboratory,7000East Avenue,L-413,Livermore,CA 94550;dtor-res@.the date of receipt and acceptance should be inserted laterAbstract.Among unidentified gamma-ray sources in the galactic plane,there are some that present significant variability and have been proposed to be high-mass microquasars.To deepen the study of the possible associa-tion between variable low galactic latitude gamma-ray sources and microquasars,we have applied a leptonic jet model based on the microquasar scenario that reproduces the gamma-ray spectrum of three unidentified gamma-ray sources,3EG J1735−1500,3EG J1828+0142and GRO J1411−64,and is consistent with the observational constraints at lower energies.We conclude that if these sources were generated by microquasars,the particle acceleration processes could not be as efficient as in other objects of this type that present harder gamma-ray spectra.Moreover,the dominant mechanism of high-energy emission should be synchrotron self-Compton (SSC)scattering,and the radio jets may only be observed at low frequencies.For each particular case,further predictions of jet physical conditions and variability generation mechanisms have been made in the context of the model.Although there might be other candidates able to explain the emission coming from these sources,microquasars cannot be excluded as counterparts.Observations performed by the next generation of gamma-ray instruments,like GLAST,are required to test the proposed model.Key words.X-rays:binaries —stars:winds,outflows —gamma-rays:observations —gamma-rays:theory1.IntroductionThe instruments EGRET 1and COMPTEL 2,onboard the Compton Gamma Ray Observatory (CGRO),detected about two hundred gamma-ray sources that still remain unidentified.Among these sources,there is a subgroup that appears to be concentrated towards the galactic plane and presents significant variability (Torres et al.2001,Nolan et al.2003).The discovery of the microquasar LS 5039,a high-mass X-ray binary (XRB)with relativistic jets,and its association with the high-energy gamma-ray source 3EG J1824−1514(Paredes et al.2000),opened the possibility that some other unidentified EGRET sources (Hartman et al.1999)could also be microquasars.That microquasars can be high-energy gamma-ray emitters has been confirmed by the ground-based Cherenkov telescope HESS,that detected a TeV source whose very small 3-σerror box contains LS 5039(Aharonian et al.2005).33EG J1735−1500and 3EG J1828+0142,at galactic lati-tudes 9◦and 6◦respectively and assuming galactic distances,are at few hundreds of parsecs above the galactic plane.It does not preclude that they are relatively young objects provided2Bosch-Ramon et al.:A microquasar model for gamma-ray sources Nolan et al.2003),and GRO J1411−64,recently dis-covered by Zhang et al.(2002)in a re-analysis of theCOMPTEL data,which is also both variable and locatedin the galactic plane.Our aim is to check whether a mi-croquasar model”under reasonable assumptions”can becompatible with the observational constraints at differentfrequencies.The contents of this paper are arranged as follows:inSect.2,the microquasar model is described;in Sect.3,theapplication of the model to each source as well as a briefdiscussion of its results and predictions are presented;thework is summarized in Sect.4.2.The microquasar modelA semi-analytical model to calculate a microquasar spec-trum from radio to gamma-rays has been developed(Bosch-Ramon et al.2005a).The scenario consists of an X-ray binary system where the compact object,a black holeor a neutron star,surrounded by an accretion disk anda corona,generates collimated outflows or jets(Mirabel&Rodr´iguez1999).The photonfields originating in thecompanion star and the corona(McClintock&Remillard2004)are taken into account.The jet is modeled as an in-homogeneous and magnetized relativisticflow of protonsand leptons,and relativistic leptons dominate the radia-tive processes.Protons will be important dynamically,andthis has been taken into account in determining the lep-tonic luminosity of the jet.This means that the total jetpower cannot be less than10times the leptonic power,since otherwise the conversion of the jet kinetic luminosityinto radiation luminosity probably would be too efficient(see Fender2001).This fact,related to the macroscopicenergy conservation law,imposes that the accretion en-ergy budget should be enough to power the whole jet(asseems to be the case in general,see Bosch-Ramon et al.2005a).Since it is not clear to what extent they are rele-vant,we have not accounted for proton radiative proper-ties.We refer to the work of Romero et al.(2003)for theradiative properties of hadronic jets in microquasars.In this leptonic model,radio emission is generated byan outer jet that expands at a lower velocity than whatis expected for the conical case.This type of expansionis introduced to simulate the particle re-acceleration pro-cesses allowing extended radio emission(i.e.through bulkmotion dissipation of energy caused by external mediuminteraction,or by instabilities in theflow of internal ori-gin).This radio jet starts where the high energy jet emis-sion is no longer significant,at about100times the dis-tance of the jet injection point to the compact object.Other works that have adopted slowly expanding jet mod-els are,for instance,Ghisellini et al.(1985)and Hjellming&Johnston(1988).In the optical-UV band,emission is inBosch-Ramon et al.:A microquasar model for gamma-ray sources36678910Log(energy photon [eV])−6−5−4−3−2−1l o g (τγγε)Fig.1.Opacities at different photon energies in the base of the jet.The dominant corona luminosity has been taken to be 3×1034erg s −1.the reference one provided the counterpart is unknown,but typical radio and X-ray fluxes of the sources found in-side those fields are taken as upper limits at these energy ranges.If the emission at these frequency bands signifi-cantly overcame the typical fluxes found in the gamma-ray error boxes,say,by one order of magnitude,the source would be barely unidentified.Lower-limits on the fluxes cannot be stated since the counterpart could be relatively quiet in radio and X-rays,being unnoticed by the surveys carried out so far over the regions corresponding to the gamma-ray error boxes.All this implies that the flux can only be constrained roughly.In the optical band,even though high-mass micro-quasars have bright stellar companions,clear counterparts have not been found in the gamma-ray error boxes.This could be explained by the strong absorption and/or en-shrouding in the optical,UV and even in the X-ray band that is often present towards the galactic plane.For in-stance,it has been suggested that obscured INTEGRAL 4sources could be intrinsically or locally obscuredinthe UVandX-ray band(e.g.Walteretal.2003).Furthermore,emission from the massive companion of an X-ray binary scattered and/or reprocessed to the far infrared could even be too weak to be detected by,for instance,the satellite IRAS (e.g.Filliatre &Chaty 2004).At the adopted dis-tances,the bright companions assumed here would present a relative brightness in the optical band of about 12mag-nitudes,if not absorbed.In the absence of specific knowledge,we have fixed the values of the jet parameters entering in the model to fiducial standards for microquasars.For the binary sys-tem parameters and jet size,we have adopted those used in Bosch-Ramon et al.(2005a),and a Lorentz factor of5/compton/data/egret/4Bosch-Ramon et al.:A microquasar model for gamma-ray sourcesTo extrapolatefluxes at lower energies,we have assumed that the variations are linked to changes in the accretion rate,linearly related to the jet power,although it is possi-ble to distinguish jet power variations from precession(see Sect.3.4).For the COMPTEL source,the average value and the maximum one are very similar because actual de-tections are similar influx,and the remaining observa-tions only were able to give upper limits for the source (see Zhang et al.2002).3.1.3EG J1735−15003EG J1735−1500was considered in the work of Torres et al.(2001)as a variable EGRET source,and in Nolan et al.(2003)it was also among the group of likely variable EGRET sources(probability∼60%).The EGRET spectrum shows a photon indexΓ∼3.2±0.5 and averageflux∼3×10−11erg s−1cm−2.The er-ror box of3EG J1735−1500was explored by Combi et al.(2003),who proposed two potential counterparts: a radio galaxy(J1737−15)and a compact radio source (PMN J1738−1502),a blazar candidate,that presents a flat radio spectrum andflux densities of about0.3Jy. However,since at the present stage it is still hard to ex-plain both whether a radio galaxy can present the variabil-ity of3EG J1735−1500and the absence of X-ray coun-terpart for the compact radio source,we have not con-sidered them as definitive solutions of the identification problem.To model the SED of a microquasar that could be the origin of the EGRET emission,we take into ac-count the known observational data and constraints at different wavelengths.If the distance were4kpc,the typ-ical luminosities of the radio sources in the EGRET error box would be of about2×1030erg s−1,the X-ray lumi-nosities would be∼1034erg s−1,and at COMPTEL en-ergies the upper limits would be∼1036erg s−1(Zhang et al.2004).The used parameter values are presented in Table1.The computed SED for both the average and the maximum luminosity levels of the gamma-ray source are shown in Fig2.It appears that3EG J1735−1500, even if detectable at X-rays during its maximum luminos-ity level,would be faint at radio wavelengths.At opti-cal wavelengths,we have computed the visual extinction of1.4magnitudes from the relationship with the hydro-gen column density found by Predehl&Schmitt(1995). It seems from Fig.2that additional intrinsic absorption would be necessary to obscure the source in the optical band to prevent an easy identification,since it still has an absolute brightness of13.4magnitudes.To reproduce the observed gamma-ray variability through the jet pre-cession,with the adopted mildly relativistic velocity of the jet,the variation in the angle should be large,reach-ing almost0◦.However,an orbital eccentricity of0.5or less could be enough to change the jet power,producing the observed ratio of maximum to average luminosity(see, e.g.,Bosch-Ramon et al.2005b).Log (photon energy [eV])2527293133353739Log(εLε[erg/s])Fig.2.SED for a broadband microquasar model of the source3EG J1735−1500.The SED of the average as well as the maximum luminosity level of the source are shown. The adopted values for the different parameters are shown in Table 1.Upper limits at radio(1),X-ray(2)and COMPTEL(3)energies,as well as the average EGRET spectrum(4),are presented.To compute the total emis-sion,the star component has been reduced a certain factor, in accordance to the maximum visual extinction found in the direction of the EGRET source.For the UV,we have followed roughly the relationship between different wave-lengths provided by Valencic et al.(2004).3.2.3EG J1828+01423EG J1828+0142is the second most variable low galac-tic latitude non-transient gamma-ray source in the list of variable EGRET sources of Torres et al.(2001),con-sidered also very variable by Nolan et al.(2003).The EGRET photon index isΓ∼2.7±0.4,with an average flux∼4×10−11erg s−1cm−2.Within the error box of this EGRET source,there are several faint non-thermal radio sources with luminosities around5×1030erg s−1 (Punsly et al.2000),and X-ray sources(observed by the ROSAT6All Sky Survey)with typical luminosities of about1033erg s−PTEL upper limits are also known(Zhang et al.2004),corresponding to luminosities of about1036erg s−1;the assumed distance still being the same.A supernova remnant(SNR),located at∼1kpc, has been proposed by Punsly et al.(2000)to be associ-ated with the object emitting at gamma-rays.This SNR, yet not part of the Green’s Catalog,was not a member of the sample in the systematic study of molecular material by Torres et al.(2003),although the source variability ar-gues against a physical association with the SNR shock. Association with the SNR would imply a lower energy re-quirement to explain the observed EGRETflux,although with such a distance the source would not be associatedBosch-Ramon et al.:A microquasar model for gamma-ray sources5 mon and specific values for the parametersStellar bolometric luminosity[erg s−1]1038Distance from the apex of the jet to the compact object[cm]5×107Initial jet radius[cm]5×106Orbital radius[cm]3×1012Viewing angle to the axis of the jet[◦]45Jet Lorentz factor 1.2Jet leptonic kinetic luminosity[erg s−1]5×103410353×1035Maximum electron Lorentz factor(jet frame)3×1034×1035×102Maximum magneticfield[G]1000050008000Electron power-law index22 1.5Total corona luminosity[erg s−1]3×10343×10333×10337http://www.parkes.atnf.csiro.au/research/surveys6Bosch-Ramon et al.:A microquasar model for gamma-ray sources−5−3−113579Log (photon energy [eV])2527293133353739L o g (εL ε [e r g /s ])total luminosity IC emission seed photons(1)(2)star ICradio jetcor. ICsync. IC starsync.cor.(3)(4)Fig.4.SED for a broadband microquasar model of GRO J1411−64.The total COMPTEL spectrum (3),the same for the average and the maximum level of emission,as well as the upper limits at radio (1),X-ray (2)and EGRET energies (4).The adopted values for the differ-ent parameters are shown in Table 1.The total emission has been reduced in the optical and ultraviolet bands ac-cording to the visual extinction in the COMPTEL source direction.high-energy gamma-rays,we will consider the sensitivity limit of EGRET in the region of GRO J1411−64as the upper limit.For this case,the average flux and the maxi-mum flux observed by COMPTEL are very similar (Zhang et al.2002).The values used to compute the SED for the different parameters are presented in Table 1and the SED is shown in Fig 4.As can be seen,the counterpart might be one of the X-ray sources detected in the COMPTEL error box but its radio emission is too faint for detection.The visual extinction within the COMPTEL error box can reach 7magnitudes.This could imply that intrinsic absorption is not required to preclude the detection of the optical and ultraviolet counterpart.3.4.Implications of the microquasar model 3.4.1.Source propertiesOur general conclusions are that,to reproduce the ob-served soft spectra at gamma-rays,a leptonic radiative process and a low maximum energy for the particles seem to be required.Generally,if the mechanism of emission were hadronic,the spectra would be harder.Moreover,comparing with two microquasar candidates likely to be gamma-ray sources,LS 5039and LS I +61303,the elec-tron maximum energies for these two cases (Bosch-Ramon &Paredes 2004a,2004b,Aharonian et al.2005)seem to be significantly higher than for the sources treated here,likely pointing to a more efficient acceleration mechanism.Inaddition,if the sources were microquasars,the dominant emitting process at high energies likely would be SSC.The dominance of SSC scattering implies that the mag-netic field is strong enough to obtain gamma-ray fluxes in agreement with observations and preventing to increase the leptonic jet power to untenable values.This would be the case if the magnetic field were too low and/or the corona scattered photons dominant.Within the context of the model,the values for the magnetic field,the jet power and the maximum electron energy distribution can be restricted to 10000G,1035erg s −1and 1GeV respec-tively.Concretely,the COMPTEL source would present slightly higher jet power and lower maximum electron energy than the two EGRET sources.Otherwise the ob-served spectrum at gamma-rays could not be reproduced taking into account the observational constraints and the previous theoretical considerations.It is worth noting that these values are coarse estimates of the source properties under a microquasar assumption,not being possible to achieve a better precision because of the lack of knowl-edge of the counterpart fluxes at low energies.Below 100keV,the spectra must be hard enough to agree with obser-vations.This means that,while for 3EG J1735−1500and 3EG J1828+0142an electron power-law index of 2is hard enough,an index of 1.5is required for GRO J1411−64to keep the X-ray fluxes to those presented by the sources in the gamma-ray error box.This could be related to a more relativistic shock acceleration in the particle injection of GRO J1411−64,and the lower maximum energy could be associated with stronger losses.We also note that the magnetic field values are 100times smaller than those of equipartition with relativistic electrons 8,which is about 106G for a leptonic jet power of 1035erg s −1.Finally,as noted above,due to the stringent constraints in X-rays,the corona should be faint,which is in agreement with the moderate X-ray emission as well as the lack of clear disk and corona features in the X-ray data of the two likely EGRET microquasars LS 5039(Bosch-Ramon et al.2005b)and LS I +61303(Leahy et al.1997).The radio jets associated with 3EG J1735−1500and 3EG J1828+0142could only be detected if the electron energy losses are very low and/or there is re-acceleration,perhaps due to shocks with the ISM at large scales or to in-ternal shocks caused by different flow velocities (Marscher &Gear 1985).In such a case,in the context of our model,there would be emission at low frequencies (be-low 1GHz)up to large distances (about 1pc).To detect it would require an instrument with low angular resolution (about 1arcmin)and high sensitivity (about 0.1mJy).For GRO J1411−64,it seems that radio emission would not be detectable due to the low maximum electron energies and the strong losses in the inner jet.Therefore,these mi-croquasars,in contrast to what is usually expected,wouldBosch-Ramon et al.:A microquasar model for gamma-ray sources7 not present clear radio jets.Instead,they would presentat most diffuse and faint radio lobes.3.4.2.VariabilityThe two mechanisms of variability that we have studiedare leptonic jet power changes,associated with accretionrate changes(e.g.for LS5039,see Bosch-Ramon et al.2005b),and precession(e.g.for LS I+61303,see Massiet al.2004;for a general case,see Kaufman Bernad´o et al.2002).We note that the plotted maximum luminositySEDs for3EG J1735−1500and3EG J1828+0142belowgamma-rays correspond to those produced by the varia-tion in the leptonic jet power.However,precession cannotbe discounted.3EG J1735−1500and3EG J1828+0142present average luminosities at gamma-rays that are closeto those of their minima(Hartman et al.1999),whichcould mean that the peaks are short duration events(e.g.periastron passage of an eccentric orbit or a minimumθduring the precession of the jet)on the timescales of theEGRET viewing periods(of about two weeks).Instead,GRO J1411−64shows a long duration burst(Zhang et al.2002),that could be more associated with a super accre-tion rate phase than to a persistent jet affected by regularchanges of its characteristics.The fact that this source ap-pears to be the brightest,assuming the same distance asfor the rest,would give weight to this option.3.4.3.PredictionsIn the radio band,a low resolution and high sensitivityinstrument would be required to detect3EG J1735−1500and3EG J1828+0142,expecting a very soft spectrum,whereas GRO J1411−64would not be detectable.If thissource is strongly absorbed in the optical and the UVband,it could be still detectable in the infrared band,with higher emission at longer than at shorter wave-lengths.However,to test such statement,the locationaccuracy of the sources should be improved,due to thelarge number of infrared sources within the gamma-rayerror boxes.At X-rays,3EG J1828+0142could be de-tected with reasonable exposure times(e.g.with XMM9),whereas3EG J1735−1500and GRO J1411−64wouldbe easily detected due to their higher emission lev-els at this energy band.For the three sources,theX-ray spectra would present photon indices of 1.5orless.We note that XMM and INTEGRAL observationsof GRO J1411−64are underway,and we will reporton 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Energy- and time-resolved detection of prompt gamma-rays for proton range verification 质子验证范围瞬发Gamma射线的能量与时间分辨检测结果分析本文章为德国慕尼黑质子治疗中心RPTC专项质子照射法临床效果研究, 目的是为了系统化地分析质子验证范围瞬发Gamma射线的能量与时间分辨检测结果Abstract摘要本研究中, 介绍了质子束验证范围的一种新颖瞬发Gamma射线探测器的实验结果.该探测系统具有一种掺铈溴化镧III级主动屏蔽闪烁器的特点, 连接着一数字数据的采集系统.数据采集与回旋加速器的射频保持了同步化, 以便分离产生自后来出现中子诱发背景下的瞬发Gamma射线信号.本研究设计了该探测器以提供高能分辨率, 以及一种可以有效降低背景事件的效果, 使得分离性质子诱发的瞬发Gamma射线被分解.对于范围验证来说, 测量分离性的瞬发Gamma射线具有几点益处.当分离性质的能量与特定的核转变相对应时, 不同大小的Gamma射线当量拥有着与质子能量独特的关联性, 并且可以直接与核反应截面相互地关联.离散Gamma射线的量化状态也能够使光束路径中组织的元素分析得到实现, 提供了一种较好预测瞬发Gamma射线照射野的效果.本研究介绍了一种在临床质子照射旋转机架内被质子笔形束扫描式照射法所照射的水幻影的实验结果.本研究采用了一个裂缝式的准直器来校准瞬发的Gamma射线, 测量值在沿范围为9, 16, 23g cm(-2)水中的质子束路径的27项位置被采集.分离性Gamma射线当量呈4.44, 5.2及6.13MeV的量化反应. 瞬发Gamma射线被发现在能量和时间维度可被清晰地分辨出. 并且具有一种与质子深度剂量曲线的可重复性相关属性.本研究的结论是, 对临床质子束活体范围验证分离性瞬发Gamma射线进行测量是可行的, 并且本研究还计划对临床使用进行进一步研究手法与探测器设计的评估.。

a rXiv:as tr o-ph/311234v11Nov23Young Neutron Stars and Their Environments IAU Symposium,Vol.218,2004F.Camilo and B.M.Gaensler,eds.Quiescent Magnetar Emission:Resonant Compton Upscattering Matthew G.Baring Rice University,Department of Physics and Astronomy,MS-108,P.O.Box 1892,Houston,TX 77251-1892,USA [baring@]Abstract.A principal candidate for quiescent non-thermal gamma-ray emission from magnetars is resonant inverse Compton scattering in the strong fields of their magnetospheres.This paper outlines expectations for such emission,formed from non-thermal electrons accelerated in a pulsar-like polar cap potential upscattering thermal X-rays from the hot stellar surface.The resultant spectra are found to be strikingly flat,with fluxes and strong pulsation that could be detectable by GLAST.1.Introduction The quiescent,non-thermal X-ray emission of soft gamma repeaters (SGRs)and anomalous X-ray pulsars (AXPs)is observed at levels that are very intense for neutron stars.It is quite possible that SGRs and AXPs emit in a broad-band,pulsar-like mode,even if the power is not of a rotational origin.A principal candidate for such emission is inverse Compton scattering,tapping abundant surface X-rays (inferred surface temperatures for AXPs and SGRs are somewhat greater than for canonical pulsars;see Perna et al.2001)as targets for energetic electrons accelerated in either polar cap or outer gap potentials.Recently,Cheng &Zhang (2001)proposed a model for significant gamma-ray emission from such magnetars,in the context of the outer gap scenario.Here,the possibility of magnetar gamma-ray emission from polar cap mod-els is explored.In the strong fields of their magnetospheres,the scattering is enhanced by the cyclotron resonance,thereby rendering polar cap models even more promising for generating hard gamma-rays that are potentially detectable by the upcoming Gamma-Ray Large Area Space Telescope (GLAST)mission.The present scenario is similar to previous pulsar (e.g.Sturner,Dermer &Michel 1995;Daugherty &Harding 1996)and old gamma-ray burst (Dermer 1990;Bar-ing 1994)models.Primary electrons with Lorentz factors up to some maximum γmax cool in collisions with the X-ray photons,in the process generating a broad spectrum extending into the gamma-ray band.This paper outlines expectations for such emission spectra,specifically in-corporating relativistic cross sections at supercritical fields that are germane to resonant Compton scattering in the magnetar regime.This investigation will focus on a simple one-zone,uniformly-magnetized region as a preparation for real geometry down the line,where the complexity of pair cascading will be explored.It is found that a very flat soft gamma-ray continuum results,with12M.G.Baringspectral cutoffs that depend strongly on the observational perspective to the field.Spectra differ significantly from those produced in outer gap models.Es-timates of the anticipatedflux indicate that GLAST may well detect magnetars in the100MeV–1GeV band if they emit efficiently like gamma-ray pulsars.2.Resonant Compton UpscatteringIn strongfields the cross section for Compton scattering is resonant at the cy-clotron energy and a series of higher harmonics(e.g.see Daugherty&Harding 1986),effectively increasing the magnitude of the process over the Thomsoncross sectionσT by of the order of1/αf B,whereαf is thefine structure con-stant.Here,as throughout the paper,magneticfields are written in units of B cr=m2e c3/(e¯h)=4.413×1013Gauss,the quantum criticalfield strength.In the non-relativistic,Thomson regime(e.g.see Herold1979),only the funda-mental resonance is retained.The dominance by the resonance leads to an effective kinematic coupling between the energiesεγm e c2andγm e c2of colliding photons and electrons, respectively,and the angle of the initial photonθγto the magneticfield lines: the cyclotron fundamental is sampled whenγεγ(1−cosθγ)=B.The simplicity of this coupling automatically implies that integration over an angular distribu-tion of incoming photons results in aflat-topped emission spectrum for Compton upscattering in strong magneticfields.This characteristic is well-documented in the literature(e.g.see Dermer1990;Baring1994;for old gamma-ray burst scenarios,and Sturner,Dermer&Michel1995for pulsar contexts),specifically for collisions between ultrarelativistic electrons and thermal X-rays emanating from a neutron star surface.For supercritical magnetar strengthfields,the Thomson regime is no longer operable,with relativistic corrections to the Compton cross section becoming requisite.These have been explored by Gonthier et al.(2000)for cases appro-priate to pulsars,namely when photons move parallel tofield lines in the electron rest frame(abbreviated ERF hereafter).The cross section is suppressed roughly by a Klein-Nishina reduction when B>∼1so that at B∼100it becomes com-parable toσT in the cyclotron resonance,and much smaller for other energies.The analytic developments of Gonthier et al.(2000)for the resonant Compton cross section are employed in the computations of this paper.The development of emission spectra requires the determination of equil-brium electron/pair distributions.The resonant upscattering of surface X-rays rapidly cools the electrons,resulting in the cessation of acceleration in the polar cap potential gap atγ<∼γmax∼3×105–106(e.g.Sturner,1995;Daugherty& Harding1996;Harding&Muslimov,1998).As the primary electrons escape the gap,they continue to cool until the photon density is diluted at altitudes above one stellar radius from the surface,when the scattering kinematics also no longer sample the resonance.The simplest description of such cooling is explored here through standard kinetic equations for development of the electron distribution. The evolution with altitude yields a mean electron distribution(i.e.averaged over the electron path to higher altitudes)that is approximately proportional to the inverse of the cooling rate˙γC.This amounts to a steep distribution(roughly ∝γ−4)for a range inγof generally at least two decades belowγmax,with aQuiescent Magnetar Emission:Resonant Compton Upscattering3 veryflat distribution(almost independent ofγ)at lower energies.There is also a“pile-up”of electrons at mildly-relativistic energies due to the concomitant inefficiency of cooling.Such shapes can be directly inferred from cooling profiles exhibited by Baring(1994)and Sturner(1995),who specialized to the magnetic Thomson limit,and extend at least in general nature to the relativistic domain, where the slopes of the primary electron distribution are modified only slightly.Figure1.The angle-integrated Fνspectra for resonant Compton up-scattering,for the two cases of B=1and B=10,withfield strengthsB expressed in terms of B cr=m2e c3/(e¯h)=4.413×1013Gauss.Thespectra are normalized for a luminosity of1033erg/sec(see text),andsource distance of10kpc,typical for AXPs and SGRs.An X-ray seedenergy ofεs=1keV was used in the models.The EGRET and GLASTflux sensitivities are also depicted.This Compton-cooled distribution was then imported into standard inte-grations for the resonant inverse Compton scattering spectrum,which in the Thomson limit were detailed,for example,in Dermer(1990)and Baring(1994). The principal complication incurred by introducing the relativistic cross section is an extra integration as a consequence of thefinite energy change of photons in the Klein-Nishina domain;this is handled routinely in the numerical inte-gration routines.Output results of these integrations are exhibited in Fig.1 for two differentfield strengths.The B=1case is similar in nature to the Thomson regime results of Dermer(1990)and Baring(1994),corresponding to aflatε−0distribution.Klein-Nishina effects manifest themselves in the B=10 case,that most appropriate to magnetars,as a spectral steepening to around anε−2/3spectrum.Both cases extend out to photon energies around1GeV, which reflect the upscattered energy from copious cooling offsurface X-rays by4M.G.Baringelectrons withγ∼γmax,These photons are highly collimated almost along the magneticfield.Some pair creation would be expected near this GeV cutoff(see the discussion of Gonthier et al2000);its exploration is deferred to future work.The normalizations for the spectra in Fig.1are established using an ob-vious observational benchmark.Since a pulsar mode for magnetar gamma-ray emission is considered here,the correlation between spin-down power˙E SD andgamma-ray luminosity L obsγobserved by the EGRET experiment on the Comp-ton Gamma-Ray Observatory(CGRO),namelyL obsγ∼1.7×1016 P2sec erg/sec,(1)can be extrapolated to the magnetar domain.This equates to roughly1032–1033erg/sec for AXPs and SGRs,corresponding approximately to their˙E SD. Note that this luminosity is still two orders of magnitude smaller than the de-tected quiescent X-ray luminosities,whose power cannot be of rotational origin.The spectra were normalized to this L obsγroughly around1GeV,for asource10kpc distant,resulting in predictedfluxes that would be detectable by GLAST,a principal conclusion of this paper.Theflat spectra strongly contrast the outer gap predictions of Cheng&Zhang(2001),which are inherently steeper due to their use of non-magnetic inverse Compton scattering.The polar cap model therefore indicates that EGRET would not have been expected to detect AXPs unless the gamma-ray luminosity was comparable to the X-ray power.Observe that potential GLAST detections would possess marked phase de-pendence.The kinematics of resonant scattering yields the strong correlation εγ∝(1−cosθγ)−1between the gamma-ray energyεγand its angle to thefield θγ,translating into much softer spectra at significant angles to thefield,i.e.out of the main pulse.Another discriminating feature is the expectation of strong polarization in the gamma-ray signal,though this cannot be probed until future generation missions.It is anticipated that any GLAST detections of AXPs or SGRs in quiescence will have a profound impact on our understanding of these sources,with potential discrimination between outer gap and polar cap models. ReferencesBaring,M.G.1994,in Gamma-Ray Bursts,eds.Fishman,G.,Hurley,K.& Brainerd,J.J.,1994(AIP Conf.Proc.307,New York)p.572. Cheng,K.S.&Zhang,L.2001,ApJ,562,918.Daugherty,J.K.,&Harding,A.K.1986,ApJ,309,362.Daugherty,J.K.,&Harding,A.K.1996,ApJ,458,278.Dermer,C.D.1990,ApJ,360,197.Gonthier,P.L.,Harding,A.K.&Baring,M.G.et al.2000,ApJ,540,907. Harding,A.K.&Muslimov,A.G.1998,ApJ,500,862.Herold,H.1979,Phys.Rev.D,19,2868.Perna,R.,et al.2001,ApJ,557,18Sturner,S.J.1995,ApJ,446,292.Sturner,S.J.,Dermer,C.D.&Michel,F.C.1995,ApJ,445,736.。

a r X i v :a s t r o -p h /0506155v 4 1 S e p 2005Mon.Not.R.Astron.Soc.000,000–000(0000)Printed 2February 2008(MN L A T E X style file v2.2)Late internal shock model for bright X-ray flares inGamma-ray Burst afterglows and GRB 011121Y.Z.Fan 1,2,3⋆and D.M.Wei 1,2⋆1Purple Mountain Observatory,Chinese Academy of Science,Nanjing 210008,China2NationalAstronomical Observatories,Chinese Academy of Sciences,Beijing 100012,China3Dept.of Physics,University of Nevada,Las Vegas,NV 89154,USA.Accepted ......Received ......;in original form ......ABSTRACTWe explore two possible models which might give rise to bright X-ray flares in GRBs afterglows.One is an external forward-reverse shock model,in which the shock param-eters of forward/reverse shocks are taken to be quite different.The other is a so called “late internal shock model”,which requires a refreshed unsteady relativistic outflow generated after the prompt γ−ray emission.In the forward-reverse shock model,after the time t ×at which the RS crosses the ejecta,the flux declines more slowly than (t ⊕/t ×)−(2+β),where t ⊕denotes the observer’s time and βis the spectral index of the X-ray emission.In the “late internal shock model”,decaying slopes much steeper than (t ⊕/t e ,⊕)−(2+β)are possible if the central engine shuts down after t e ,⊕and the observed variability timescale of the X-ray flare is much shorter than t e ,⊕.The sharp decline of the X-ray flares detected in GRB 011121,XRF 050406,GRB 050502b,and GRB 050730rules out the external forward-reverse shock model directly and favors the “late internal shock model”.These X-ray flares could thus hint that the central engine operates again and a new unsteady relativistic outflow is generated just a few minutes after the intrinsic hard burst.Key words:Gamma Rays:bursts −ISM:jets and outflows–radiation mechanisms:nonthermal −X-rays:general1INTRODUCTIONGRB 011121was simultaneously detected by BeppoSAX GRBM and WFC (Piro 2001),and the fluence in the 2-700keV range corresponds to an isotropic energy of 2.8×1052ergs at the redshift of z =0.36(Infante et al.2001).This burst was born in a stellar wind (Price et al.2002;Greiner et al.2003)and a supernova bump was detected in the late op-tical afterglow (Bloom et al.2002;Garnavich et al.2003).Its very early X-ray light curve,which has not been published until quite recently,is characterized by the presence of two flares (Prio 2005,hereafter P05).In the first one,which is also the strongest of the two,the observed flux F rises and decays very steeply:F ∝t 10⊕for 239s <t ⊕<270s andF ∝t −7⊕for 270s <t ⊕<400s,where t ⊕is the observer’s time 1.Such a peculiar flare in the early X-ray lightcurve of⋆E-mail:yzfan@(YZF);dmwei@(DMW)1During our revision,bright X-ray flares peaking a few minutes after XRF 050406,GRB 050502b and GRB 050730have been reported (Burrows et al.2005;Starling et al.2005).Sharp rise and fall are also evident in these events.GRBs has not been predicted before.P05suggested that the X-ray flare represents the beginning of the afterglow.In this Letter we explore two alternative models which might give rise to very early X-ray flare in GRB afterglows (§2):a forward-reverse shock model (§2.1)and a “late in-ternal shock model”(§2.2).We compare the available data with the predictions of those models in §3and summarize our results in §4,with some discussion.2POSSIBLE MODELS2.1The external forward-reverse shock modelThe external forward-reverse shock model has been widely accepted on interpreting the early IR/optical flashes of GRB 990123,GRB 021211and GRB 041219a (For observations,see:Akerlof et al.1999;Fox et al.2003;Li et al.2003;Blake et al.2005.For theoretical modeling,see:Sari &Piran 1999;M´e sz´a ros &Rees 1999;Wei 2003;Kumar &Panaitescu 2003;Fan,Zhang &Wei 2005).Synchrotron radiation from the reverse shock (RS)and the forward shock (FS)usually peaks in the infrared-to-optical and ultraviolet-to-soft X-ray bands,respectively.Thus,the RS emission component2is not dominant in the X-ray band.The synchrotron self-Compoton(SSC)scattering effect of the RS radiation has also been considered by different authors,but no strong X-ray emission is found to be expected(Wang,Dai&Lu2001) except in some carefully balanced conditions(Kobayashi et al.2005).In most of previous works,the fractions of FS energy given to electrons,ǫe,and to magneticfield,ǫB,were as-sumed to be the same as the corresponding fractions in the RS.However,this may not necessary be the case.Fan et al. (2002)performed a detailedfit to the opticalflash of GRB 990123data and obtainedǫr e=4.7ǫf e andǫr B=400ǫf B,where the superscripts“r”and“f”represent RS and FS,respec-tively.Similar results were obtained by Zhang,Kobayashi& M´e sz´a ros(2003),Kumar&Panaitescu(2003),Panaitescu &Kumar(2004),McMahon,Kumar&Panaitescu(2004), and Fan et al.(2005).In this section,we study the RS/FS emission in X-ray band by adopting different shock param-eters.We focus on the thin shell case(i.e.,the RS is sub-relativistic,see Kobayashi[2000]),in which the RS emission is well separated from the promptγ−ray emission.ISM model.In the thin shell case,the observer’s time at which RS crosses the ejecta can be estimated by(e.g., Fan et al.2005)t×≈128s(1+z1+z)(1+Y f)−2,νf m,⊕=4.4×1015Hz E12B,−3ǫ2e,−1t−31+z),andF fν,max=2.6mJy E iso,53ǫ1/2B,−3n1/2D−2L,28.34(1+z1+4x fǫf e/ǫfB]/2is the Compton parameter, x f≈min{1,(νf m/νf c)(p−2)/2}(Sari&Esin2001),and D L is the luminosity distance for(ΩM,ΩΛ,h)=(0.3,0.7,0.71). Hereafter t=t⊕/(1+z),and t d is in unit of days.Following Zhang et al.(2003),we takeǫr e=R eǫf e and ǫr B=R2Bǫf B.At t×,the RS emission satisfies[See also Fan et al.(2005),note that a novel effect taken into account here is the inverse Compton cooling of the electrons]νr m,⊕(t×)=R B[R e(γ34,×−1)]2νf m,⊕(t×)/(Γ×−1)2,(2)νr c,⊕(t×)≈R−3B[(1+Y f)/(1+Y r)]2νf c,⊕(t×),(3) F rν,max(t×)≈ηR B F fν,max(t×).(4) whereγ34,×≈(η/Γ×+Γ×/η)/2is the Lorentz factor of the shocked ejecta relative to the initial one,Γ×is the bulk Lorentz factor of the shocked ejecta at t×,Y r≃[−1+ F fν⊕(t×)≈ηR p−2Γ×−1)p−1(1+Y f3Figure1.The very early X-ray(νx=2.42×1017Hz)samplelightcurves.For the reverse shock emission component,R e andR B have been marked in thefigure.(a)The ISM case,the param-eters are taken as n=1cm−3,E iso,53=1,z=1,∆=6×1011cm,ǫf e=0.1,ǫfB =0.001,η=200,and p=2.4.(b)The windcase,following P05,we take A∗=0.003,ǫf e=0.01,ǫfB =0.5,E iso,53=0.28,p=2.5,and z=0.36;In addition,we assume η=200and∆=3.0×1012cm.is too shallow compared to the steep decay of X-rayflares observed so far(see Fig.1).2.2Late internal shock modelIn the standardfireball model of GRBs,theγ−ray emission is powered by internal shocks,whose duration depends on the active time of the central engine.However,the variability of some GRB afterglows implies that the activity of the GRB central engine may last much longer than the duration of the prompt emission recorded byγ−ray monitors(e.g.,Dai &Lu1998;Granot,Nakar&Piran2003;Ioka,Kobayashi &Zhang2005).In addition,it has been proposed that the Fe line observed in some GRB X-ray afterglows could be attributed to a prolonged activity of the central engine(Rees &M´e sz´a ros2000;Gao&Wei2005).A possible mechanism for the re-activity of the central engine could be as follows.During the accretion phase which powers the promptγ−ray emission,a fraction of the mate-rial constituting the massive progenitor could possibly be pulled out;the central engine could thus be restarted at late times by the fall back of part of this material onto the central collapsar remnant(King et al.2005).Here we assume that the central engine restarts a few minutes after the promptγ−ray emission,powering a new unsteady relativistic outflow.We suppose that the Lorentzfactor of the ejected material can be highly variable,set-tingΓs∼10andΓf∼100,as the typical Lorentz factors of the slow and fast shells,respectively.The masses of theslow and fast shells are taken as m f≃m s.When an inner fast shell catches up with an outer slow shell at a radius ∼2Γ2s cδt⊕/(1+z)(whereδt⊕is the observed typical vari-ability timescale of the X-rayflares),internal shocks are gen-erated.The Lorentz factor of the merged shell isΓ≈√Γf/Γs+42.2.2The synchrotron radiation of the“late internal shocks”Following Dai &Lu (2002),the comoving number den-sity of the unshocked outflow is estimated by n e ≈L m /(4πΓ2R 2int m p c 3),where m p is the rest mass of proton.The thermal energy density of the shocked material is cal-culated by e ≈4Γsh (Γsh −1)n e m p c 2(Blandford &McKee 1977).The intensity of the generated magnetic field is es-timated by B ≈(8πǫB e )1/2≈6×103G ǫ1/2B ,−1[Γsh (Γsh −1)/2]1/2L 1/2m ,49.7Γ−11.5R −1int ,14.5.As usual,we assume that in the shock front,the accel-erated electrons distribute as dn e /dγe ∝γ−pe for γe >γe ,m ,where γe ,m =ǫe (Γsh −1)[(p −2)m p ]/[(p −1)m e ]is the min-imum Lorentz factor of the shocked electrons (Sari et al.1998),and m e is the rest mass of electron.In this section,we take p=2.5.The observed typical frequency of the syn-chrotron radiation readsνm ,⊕=γ2e ,m q e ΓB/[2(1+z )πm e c ]≃2.7×1016Hz ǫ2e ,−0.3ǫ1/2B ,−1(Γsh −1)5/2(Γsh /2)1/2L 1/2m ,49.7Γ−21.5δt −1⊕,1,(9)i.e.,most of the shock energy is emitted in the soft X-rayband,where q e is the charge of electron.The cooling Lorentz factor is estimated by (e.g.,Sari et al.1998)γe ,c ≈7.7×108(1+z )/(ΓB 2δt ⊕),and the corre-sponding cooling frequency reads νc ,⊕=γ2e ,c q e ΓB/[2(1+z )πm e c ]≃1010Hz [1.36/(1+z )]2ǫ−3/2B ,−1Γ81.5[Γsh (Γsh −1)/2]−3/2L −3/2m ,49.7δt ⊕,1.(10)The synchrotron self-absorption frequency is estimated by(Li &Song 2004)νa ,⊕≃1015Hz [1.36/(1+z )]3/7L 2/7m ,49.7Γ−5/71.5δt −4/7⊕,1B 1/73.(11)The maximum spectral flux of the synchrotron radiation is (e.g.,Wijers &Galama 1999)F max ≈3√53DECLINE BEHA VIOR OF THE X-RAY FLARE:CONSTRAINT ON THE MODELEarly X-rayflares have been well detected in GRB011121, XRF050406,GRB050502b and GRB050730(P05;Burrows et al.2005;Staring et al.2005).The rise and fall of thefirst flare(also the dominant one)in GRB011121are both very steep.Similar temporal behavior is evident in other events. The sharp decline of theseflares imposes a robust constraint on the model,as shown below.The X-rayflare detected in GRB011121appears at t b,⊕=239s and peaks at t p,⊕=270s.The burst is believed to be born in a weak stellar wind.As shown in Fig.1(b), noflare is expected in the FS-RS model.The FS-RS shock model is further disfavored by its shallow decline.In the late internal shock model,the decline of theflare can be steep enough to account for the observation(see Fig.2for illustra-tion).Moreover,as shown in§2.2.2,with proper parameters the observedflux can be well reproduced.So the“late inter-nal shock model”is favored.We would like to point out that the fall of the X-rayflare detected in GRB011121is still at-tributed to the late internal shocks rather than the curvature effect.The reason is as follows.Sinceδt⊕≤(t p,⊕−t b,⊕)=31 s,the resulted decline Fνx∝[1+(t⊕−270)/δt⊕]−3.15is much steeper than the observation Fνx∝[(t⊕−239)/31]−1.4(see Fig.7of P05)if after t p,⊕there are no internal shocks any more.The X-rayflare detected in XRF050406peaks at t p,⊕≈210s and declines as F∝t−5.7⊕.The X-rayflare detected in GRB050502b peaks at t p,⊕≈650s and declines as F∝t−7⊕.In the X-ray afterglow lightcurve of GRB050730,there are three X-rayflares(ranging from200s to800s after the trigger of the GRB).A crudefit to the decline of these threeflares results in F∝t−5⊕or steeper.Obviously,the FS-RS scenario is ruled out by the steep observed decays and the“late internal shock model”is favored.For the X-rayflare detected in GRB050502b,the late internal shock model interpretation is further supported by the sharp spike detected in1.0−10.0keV band(Burrows et al.2005).4SUMMARY&DISCUSSIONIn this work,we have explored two possible models which might give rise to X-rayflares in GRB afterglows.One is the external forward-reverse shock model(the ISM case),in which the shock parameters of forward/reverse shocks are taken to be quite different.The other is the“late internal shock model”,which requires that a refreshed unsteady rela-tivistic outflow is generated after the promptγ−ray emission (see Ramirez-ruiz,Merloni&Rees[2001]for alternative sce-narios),perhaps due to the fallback accretion onto the central collapsar remnant.The refreshed outflow may be character-ized by a low outflow luminosity(∼1049ergs s−1),a small bulk Lorentz factor(∼30),and a long variability timescale (∼10s).In the external forward-reverse shock model,after the peak of the reverse shock emission(t p,⊕=t×),theflux can not decline more sharply than(t⊕/t p,⊕)−(2+p/2)(see Fig.1for illustration).In the“late internal shock model”, the decline can be much steeper than(t⊕/t e,⊕)−(2+p/2)if the central engine shuts down after t e,⊕and the longest variabil-ity timescale of the X-rayflare is much shorter than t e,⊕(see Fig.2for illustration).For the X-rayflares detected in GRB011121,XRF 050406,GRB050502b and GRB050730,the external forward-reverse shock model is ruled out directly by its shal-low temporal decay.For the same reason,other possible ex-ternal models(i.e.,the model related to the external for-ward shock),including the density jump model,the two-components jet model,the patch jet model as well as the energy injection model are ruled out too(Zhang et al.2005). Thus,the“late internal shock model”is found to be favored. In this model,the optical emission may be suppressed due to strong synchrotron-self-absorption.But in the ultraviolet band,the radiation could be quite rge amount of neutral gas would be ionized,as detected in GRB050502b and GRB050730(Burrows et al.2005;Starling et al.2005).Very early X-rayflares are well detected both in long GRBs and in XRFs,which strengthens the correlation of these two phenomena,though the nature of XRFs is still unclear(Barraud et al.2005and the references therein).Finally,we suggest that the early X-ray light curve of some GRBs may be a superposition of the emission powered by the long activity of the central engine and the emission of the external forward shock.As a consequence,the X-ray temporal behavior may be quite different from that of the long wavelength emission(UV/Optical ones).This predic-tion can be tested by the UVOT and XRT on board Swift observatory directly in the near future. ACKNOWLEDGMENTSWe thank Bing Zhang and E.W.Liang for informing us Piro et al.’s paper on GRB011121at the end of Feb,and G.F.Jiang,L.J.Gou,Z.Li and H.T.Ma for kind help.We also appreciate the referees for their helpful comments and the third referee for her/his great help.This work is sup-ported by the National Natural Science Foundation(grants 10225314and10233010)of China,and the National973 Project on Fundamental Researches of China(NKBRSF G1*******).REFERENCESAkerlof C.et al.1999,Nature,398,400Barraud C.,Daigne F.,Mochkovitch R.,Atteia J.L.2005,A&A, in press(astro-ph/0507173)Blandford,R.D.,&McKee,C.F.1977,MNRAS,180,343 Blake C.H.et al.2005,Nature,435,181Bloom J.S.,et al.2002,ApJ,572,L45Burrows,D.N.,et al.2005,Science,in press(astro-ph/0506130) Dai Z.G.,Lu T.,1998,A&A,333,L87Dai Z.G.,Lu T.,2002,ApJ,580,1013Daigne F.,Mochkovitch R.1998,MNRAS,296,275Daigne F.,Mochkovitch R.2000,A&A,358,1157Fan Y.Z.,Dai Z.G.,Huang Y.F.,Lu T.,2002,Chin.J.Astron.Astrophys.2,449(astro-ph/0306024)Fan Y.Z.,Wei D.M.,Wang C.F.,2004,A&A,424,477Fan Y.Z.,Zhang B.,Wei D.M.,2005,ApJ,628,L25Fox D.et al.2003,ApJ,586,L5Gao W.H.,Wei D.M.,2005,ApJ,628,853Garnavich P.M.,et al.2003,ApJ,582,924Granot J.,Nakar E.,Piran T.,2003,Nature,426,138Greiner J.,et al.2003,ApJ,599,12236Infante L.,Garnavich P.M.,Stanek K.Z.,Wyrzykowski L.,2001, GCN Circ.,1152Ioka K.,Kobayashi S.,Zhang B.,2005,ApJ,in press(astro-ph/0409376)King A.,O’Brien P.T,Goad M.R.,Osborne J.,Olsson E.,Page K.2005,ApJL,in press(astro-ph/0508126)Kobayashi S.2000,ApJ,545,807Kobayashi S.,Zhang B.,M´e sz´a ros P.,Burrows W.,2005,ApJL, submitted(astro-ph/0506157)Kumar P.,Panaitescu A.,2003,MNRAS,346,905Kumar P.,Panaitescu A.,2000,ApJ,541,L51(KP00)Kumar P.,Piran T.,2000,ApJ,532,286Li Z.,Song L.M.2004,ApJ,608,L17Li W.D.,Filippenko A.V.,Chornock R.,Jha S.,2003,ApJ,586, L9Lloyd-Ronning,N.M.,&Zhang,B.2004,ApJ,601,371 MacFadyen A.I.,Woosley S.E.,Herger A.2001,ApJ,550,410 McMahon E.,Kumar P.,Panaitescu A.,2004,MNRAS,354,915 M´e sz´a ros P.,Rees M.J.,1999,MNRAS,306,L39Paczy´n ski B.,Xu G.H.,1994,ApJ,427,708Panaitescu A.,Kumar P.,2004,MNRAS,353,511Panaitescu A.,M´e sz´a ros P.,Rees M.J.,1998,ApJ,503,314 Piran T.,1999,Phys.Rep.,314,575Piro L.,2001,GCN Circ.1147Piro L.et al.,2005,ApJ,623,314(P05)Price P.A.,et al.2002,ApJ,572,L51Ramirez-Ruiz E.,Merloni A.,Rees M.J.,2001,MNRAS,324, 1147Rees M.J.,M´e sz´a ros P.,1994,ApJ,430,L93Rees M.J.,M´e sz´a ros P.,1998,ApJ,496,L1Rees M.J.,M´e sz´a ros P.,2000,ApJ,545,L73Sari R.,Esin A.A.2001,ApJ,548,787Sari R.,Piran T.1999,ApJ,517,L109Sari R.,Piran T.,Narayan R.1998,ApJ,497,L17Starling R.L.C.,et al.2005,A&A,submitted(astro-ph/0508237) Wang X.Y.,Dai Z.G.,Lu T.,2001,ApJ,556,1010Wei D.M.2003,A&A,402,L9Wijers R.A.M.J.,&Galama T.J.1999,ApJ,523,177Zhang B.,Fan Y.Z.,Dyks J.,Kobayashi S.,M´e sz´a ros P.,BurrowsD.N.,Nousek J.A.,Gehrels N.2005,ApJ,submitted(astro-ph/0508321)Zhang B.,Kobayshi S.,M´e sz´a ros P.,2003,ApJ,595,950 Zhang B.,M´e sz´a ros P.,2002,ApJ,566,712Zou Y.C.,Wu X.F.,Dai Z.G.,2005,MNRAS,in press(astro-ph/0508602)APPENDIX A:DERIV ATION OF THECUR V ATURE EFFECTAssuming a shell is ejected at t eje and moves with a constant Lorentz factorΓ(the corresponding velocity is V,in unit of the speed of light),the electrons are shock-accelerated at R<R cro and cools rapidly,where R cro is the radius after which there is no newly relativistic electrons injected. For R>R cro,the radiation nearly cuts offas long as the observer frequencyν⊕is above the cooling frequency of the electrons.For t⊕>t0≡t eje+(1+z)R cro/(2Γ2c),theflux received from the shell is given byFν⊕(t⊕)∝ θjθt Sν′sinθdθ2+β+k(1−V cosθt)−(2+β).(A2)On the other hand,Fν(t0)∝11−V]−(2+β)∝(t⊕−t eje。

a rXiv:as tr o-ph/21160v11Jan22Gamma-Ray Summary Report J.Buckley ∗Washington University,St.Louis T.Burnett †University of Washington G.Sinnis ‡Los Alamos National Laboratory P.Coppi §Yale University P.Gondolo ¶Case Western Reserve University J.Kapusta ∗∗University of Minnesota J.McEnery ††University of Wisconsin J.Norris ‡‡NASA/Goddard Space Flight Center P.Ullio §§SISSA D.A.Williams University of California Santa Cruz ¶¶(Dated:February 1,2008)This paper reviews the field of gamma-ray astronomy and describes future experiments and prospects for advances in fundamental physics and high-energy astrophysics through gamma-ray measurements.We concentrate on recent progress in the understanding of active galaxies,and the use of these sources as probes of intergalactic space.We also describe prospects for future experi-ments in a number of areas of fundamental physics,including:searches for an annihilation line from neutralino dark matter,understanding the energetics of supermassive black holes,using AGNs as cosmological probes of the primordial radiation fields,constraints on quantum gravity,detection of a new spectral component from GRBs,and the prospects for detecting primordial black holes.I.INTRODUCTIONWith new experiments such as GLAST and VERITAS on the horizon,we are entering an exciting period for gamma-ray astronomy.The gamma-ray waveband has provided a new spectral window on theuniverseand has already resulted in dramatic progress in our understanding of high energy astrophysical phenomena. At these energies the universe looks quite different then when viewed with more traditional astronomical tech-niques.The sources of high energy gamma rays are limited to the most extreme places in the universe:the remnants of exploding stars,the nonthermal Nebulae surrounding pulsars,the ultra-relativistic jets emerging from supermassive black holes at the center of active galaxies,and the still mysterious gamma-ray bursters. While understanding these objects is of intrinsic interest(how does nature accelerate particles to such high energies?how do particles andfields behave in the presence of strong gravitationalfields?),these objects can also be used as probes of the radiationfields in the universe and possibly of spacetime itself.In this case,the astrophysics of the object is a confounding factor that must be understood to produce a quantitative measurement or a robust upper limit.While some may view this as a limitation of such indirect astrophysical measurements,in most cases there are no earth-bound experiments that can probe the fundamental laws of physics at the energy scales available to gamma-ray instruments.Gamma-ray astronomy has developed along two separate paths.From the ground,simple,inexpensive exper-iments were built in the1950’s to observe the Cherenkov light generated by extensive air showers generated by photons with energies above several TeV.Despite decades of effort it was not until the late1980’s that a source of TeV photons was observed.There are now roughly10known sources of TeV gamma rays,three galactic sources and at least three active galaxies.From space,the COS-B satellite,launched in1975,observed thefirst sources of cosmic gamma rays at energies above70MeV.The launch of the Compton Gamma Ray Observatory (CGRO)in1991,with the Energetic Gamma Ray Experiment Telescope(EGRET)instrument,brought thefield to maturity.Whereas COS-B discovered a handful of sources,EGRET observed over65active galaxies[1],seven pulsars,many gamma-ray bursts,and over60sources that have no known counterparts at other wavelengths. The disparity in the development of the two techniques can be traced to the extremely lowfluxes of particles present above a TeV(∼4γfootballfield−1hr−1)and the cosmic-ray background.Above the earth’s atmosphere, one can surround a gamma-ray detector with a veto counter that registers the passage of charged particles. From the ground,one is forced to infer the nature of the primary particle by observing the secondary radiation generated as the extensive air shower develops.It was not until such a technique was developed for air Cherenkov telescopes[2],that sources of TeV photons were discovered.Despite these difficulties a new generation of ground-based instruments is under development that will have a sensitivity that will rival that of space-based instruments.At the same time a space-based instrument,GLAST,with a relatively large area(∼1m2)and excellent energy and angular resolution is scheduled to be launched in2005.In this paper we will give a brief survey of the gamma-ray universe and demonstrate some of the fundamental measurements(relevant to particle physicists)that can be made using distant objects that emit high-energy photons.What will hopefully become clear from this exposition are some development paths for future instru-ments.The need to see to the far reaches of the universe,makes a compelling case for ground-based instruments with energy thresholds as low as10GeV.The need to detect and study the many transient phenomena in the universe makes a compelling case for the development of an instrument that can continually monitor the entire overhead sky at energies above∼100GeV with sensitivities approaching that of the next generation of pointed instruments.As with any new branch of astronomy,it is impossible to predict what knowledge will ultimately be gained from studying the universe in a different waveband,but early results hint at a rich future.New and planned instruments with greatly increased sensitivity will allow us to look farther into the universe and deeper into the astrophysical objects that emit gamma rays.Gamma-ray astronomy can be used to study the most extreme environments that exist in the universe,and may also provide a number of unique laboratories for exploring the fundamental laws of physics at energies beyond the reach of earth-bound particle accelerators.II.PHYSICS GOALS OF GAMMA RAY ASTRONOMYA.Active Galactic NucleiActive galactic nuclei(AGN)are believed to be supermassive black holes,108−1010M⊙,accreting matter from the nucleus of a host galaxy.The accretion of matter onto a black hole is a very efficient process,capable of releasing∼10%of the rest energy the infalling matter(∼40%for a maximally rotating black hole).(For comparison fusion burning in stars releases∼0.7%of the rest energy.)Radio loud AGN emit jets of relativistic particles,presumably along the rotation axis of the spinning black hole.The COS-B instrument observed the first AGN in the gamma-ray regime(E>100MeV),3C273.But it was not until the launch of the CGRO and EGRET that many AGN could be studied in the gamma-ray regime.More recently,ground-based instruments have extended these observations into the TeV energy band.The energy output of these objects in gamma rays is of order1045ergs s−1,and many of these objects emit most of their energy into gamma rays.The relativisticmotion has several effects:1)the energy of the photons is blue-shifted for an observer at rest(us),2)the timescale is Lorentz contracted(further increasing the apparent luminosity),and3)the relativistic beaming suppresses photon interactions.Thus,one expects that AGN observed in the TeV regime should have their jets nearly aligned with our line-of-sight.The types of AGN detected at high energies,which includeflat spectrum radio quasars(FSRQs)and BL Lacertae(BL Lac)objects,are collectively referred to as blazars.The Whipple Observatory10m atmospheric Cherenkov telescope demonstrated that the emission spectra of several blazars extend into TeV energies.Two of these detections(Markarian421and Markarian501)have been confirmed by independent experiments(CAT and HEGRA),at significance levels of between20σin a half hour to80σfor a season.Blazar emission is dominated by highly variable,non-thermal continuum emission from an unresolved nucleus. The broadband emission and high degree of polarization suggest synchrotron radiation extending from radio up to UV or even hard X-ray energies.The short variability timescales and high luminosities are thought to result from highly relativistic outflows along jets pointed very nearly along our line of sight.The spectral energy distributions(SEDs)of these objects have a double-peaked shape(see Figure1)with a synchrotron component that peaks in the UV or X-ray band,and a second component typically rising in the X-ray range and peaking at energies between∼1MeV and1TeV[3].The most natural explanation of the second peak is inverse-Compton scattering of ambient or synchrotron photons[4]although other possibilities such as proton-induced cascades have not been ruled out[5].These two models have somewhat complementary strengths and weaknesses.Since electrons are lighter than protons,they can be confined in a smaller acceleration region but lose energy more quickly(by synchrotron and IC emission),making it difficult to accelerate electrons to extreme energies.For hadronic models,very high energies can be attained given sufficient time,a large acceleration region and high magneticfields.However,the short variability timescales,implying short acceleration times and compact regions are difficult to explain.In addition,the electron models make natural predictions on the correlation between X-ray and gamma ray luminosities.While it has been claimed that proton models can be constructed that explain these correlations,detailed calculations have not appeared in the literature.Whipple observations of the vast majority of EGRET blazars have yielded only upper limits[6,7,8];Mrk421 (z=0.031)[9]being the exception.Subsequent searches for emission from X-ray bright BL Lac objects has led to the detection of Mrk501(z=0.034)[10],and four other as yet unconfirmed sources[1ES2344+514 (z=0.044[11],1ES2155-304(z=0.117)[12],1ES1959+650(z=0.048)[13]and1H1426+428(z=0.13)[14]]. The SEDs observed for these sources show higher energy synchrotron andγ-ray peaks,and comparable power output at the synchrotron andγ-ray peak.These observations are well described by the classification scheme of Padovani and Giommi[15].The AGN detected by EGRET are all radio-loud,flat-spectrum radio sources and lie at redshifts between0.03and2.28. They are characterized by two component spectra with peak power in the infrared to optical waveband and in the10MeV to GeV range.For many of the GeV blazars,the total power output of these sources peaks in the gamma-ray waveband.The objects detected at VHE,appear to form a new class distinct from the EGRET sources.All are classified as high-energy peaked[15]BL Lacs(HBLs)defined as sources with their synchrotron emission peaked in the UV/X-ray band and gamma-ray emission peaking in the∼100GeV regime(see,e.g.,Fig.1).The correspondence of the position of the peak of the synchrotron andγ-ray energy is naturally explained in models where the same population of electrons produces both spectral components.Proton induced cascade models[5]might also reproduce the spectra,but have no natural correlation in the cutoffenergy of the two components,or the observed correlated variability.Another difference in the VHE detections is that only the nearest sources with redshifts z<∼0.1have been detected.The sensitivity of EGRET for a one-year exposure is comparable to that of Whipple for a50hour exposure for a source with spectral index of2.2.The failure of ACTs to detect any but the nearest AGNs therefore requires a cut-offin theγ-ray spectra of the EGRET sources between10GeV and a few hundred GeV. This cutoffcould be intrinsic to the electron acceleration mechanism,due to absorption offof ambient photons from the accreting nuclear region[16],or caused by absorption via pair production with the diffuse extragalactic background radiation[17,18].While the latter mechanism establishes an energy-dependent gamma-ray horizon it can also be used to measure the radiationfields thatfill intergalactic space.In the framework of Fossati et al.,[19]the low energy peaked EGRET BL Lacs(LBLs)correspond to AGNs with a more luminous nuclear emission component than HBLs.The relatively high ambient photon density in the LBLs is up-scattered by relativistic electrons toγ-ray energies.With high enough ambient photon densities, the resulting inverse-Compton emission can exceed that resulting from the up-scattering of synchrotron photons. This accounts for the observation of relatively high levels of gamma-ray emission,dominating the power output over the entire spectrum.The higher luminosity could also shut down the acceleration process at lower energies.For lack of another viable hypothesis,consider the common hypothesis that the energetic particles in AGNs come from electronsor protons accelerated by relativistic shocks traveling down the AGN jets.In the model of diffusive shock acceleration(essentially thefirst order Fermi process),particles are accelerated as they are scattered from magnetic irregularities on either side of a shock.For strong,non-relativistic shocks,a constant escape probability with each shock crossing results in an∼E−2spectrum,close to that observed.More realistic models including nonlinear effects lead to slightly steeper spectra;if the shock velocity is relativistic the spectral index may range from1.7to2.4.In any event,an electron spectrum∼E−γwill give rise to synchrotron radiation with a spectral indexα=(γ−1)/2,in good agreement with observations.The maximum energy attainable is given by equating the rate of energy loss from synchrotron emission or inverse-Compton emission to the acceleration rate as given by the shock parameters.In the low-energy peaked objects,it is thought that high ambient photon densities result in inverse-Compton losses that dominate over synchrotron losses and limit the maximum electron energy achieved by shock acceleration.Thus one also obtains a natural explanation for the lower energies of the peak synchrotron and IC power in these objects.In HBLs, the ambient photonfields are presumably weaker and self-Compton emission dominates over Comptonization of external photons(EC).Electrons can reach higher energies by shock acceleration,and the peaks in the SED move to higher energies and have more nearly equal peak power.This model is consistent with the data and serves as a useful paradigm for searching for new VHE sources.The SEDs shown in Fig.1,combine the results of a number of different measurements of the X-ray and VHE spectra of Mrk501,and compare them with simple synchrotron self-Compton(SSC)models(see Buckley[20] and references therein).The agreement between the spectral measurements and the model is exceptionally good for Mrk501.1.Multiwavelength Observations:VariabilityData taken on Mrk421over the years1995[21]to2001[22]show that theγ-ray emission is characterized by a succession of approximately hour-longflares with relatively symmetric profiles(see Figure2).While most of the multiwavelength observations of Mrk421show evidence for correlated X-ray and gamma ray variability,the nature of the correlation is unclear and the data have traditionally undersampled the variability. However,a multi-wavelength campaign conducted on Mrk501in1997revealed a strong correlation between TeVγ-rays and soft X-rays(the50–500keV band detected by OSSE)(Fig.1).Recent multiwavelength observations of Mrk421made during the period March18,2001to April1,2001 with the Whipple gamma-ray telescope,and the Proportional Counter Array(PCA)detector on the Rossi X-ray Timing Explorer(RXTE)better sample the rapid variability of Mrk421.Key to the success of this campaign is the nearly continuous>330ks exposure with RXTE[23].Numerous ground-based atmospheric Cherenkov and optical observations were scheduled during this period to improve the temporal coverage in the optical and VHE bands.Frequent correlated hour-scale X-ray andγ-rayflares were observed.Fig.2shows a subset of these data showing the close correlation of the well-sampled TeV and X-ray(2–10keV)lightcurves on March 19,2001[22].Leptonic models provide a natural explanation of the correlated X-ray and gamma-rayflares,and can re-produce the shape of theflare spectrum.The simplest model for blazar emission is the one-zone synchrotron self-Compton(SSC)model where energetic electrons in a compact emission region up-scatter their own syn-chrotron radiation.As shown in Fig.1,such a model results in surprisingly goodfits to the Mrk501SED. In the SSC model,the intensity of the synchrotron radiation is proportional to the magnetic energy density and the number density of electrons I synch∝n e.Since these same electrons up-scatter this radiation,the IC emission scales as I IC∝n2e.Thus we expect I IC∝I2synch.Krawczynski et al.,[24]examined the correlation of TeVγ-ray and X-ray intensity for several strongflares of Mrk501in1997.The results,plotted in Figure3,show evidence for such a quadratic dependence.(However the possibility of a baseline level of the X-ray emission can not be excluded.)While the interpretation of these observations is not unambiguous,this analysis is an important example of what can be learned with continued multiwavelength studies of AGNs.How do these observations constrain the alternative hypothesis that proton induced cascades(PIC),not elec-trons,are responsible for the gamma-ray emission?In the hadronic models of Mannheim and collaborators,the gamma-ray emission typically comes from synchrotron emission from extremely energetic,secondary electrons produced in hadronic cascades.Since a viable hadronic target for pp→ppπappears to be lacking(except per-haps in the broad line clouds),the assumption is made that the cascade begins with ultrarelativistic particles interacting with ambient photons to produce pions.This implies proton energies in excess of10∼16eV.The neutral pions presumably give rise to gamma rays and electromagnetic cascades,while the charged pions could give a neutrino signal.These models have attracted much interest since,in the most optimistic cases,these models may produce an observable neutrino signal and may provide a mechanism for producing the ultra-high energy cosmic rays.If the sources are optically thick to the emerging protons(i.e.,they absorb some fractionThis figure is available as p42_fig1a.gif051000.51100200300120.80.91F l u x (γ/m i n )F l u x (c n t s /s )F l u x (c n t s /s )F l u x (c n t s /s )MJDF l u x (a r b i t r a r y u n i t s )FIG.1:Left:SED of Mrk 501from contemporaneous and archival observations.Right:Multi-wavelength observations of Mrk 501;(a)γ-ray,(b)hard X-ray,(c)soft X-ray,(d)U-band optical light curves during the period 1997April 2–20(April 2corresponds to MJD 50540).The dashed line in (d)indicates the optical flux in 1997March.(from [20]and references therein.)This figure is available as p42_fig2.gifFIG.2:Simultaneous X-ray/γ-ray flare observed on March 19,2001.The 2–10keV X-ray light curve was obtained with the PCA detector on RXTE [22,23];data points are binned in roughly 4minute intervals.of the cosmic rays,but not the neutrinos)then it may be possible to produce a relatively large neutrino signal without overproducing the local cosmic ray flux [25].While these models have a number of attractive features,there is some debate about whether they can provide a self-consistent description for the observations.To overcome the threshold condition for pion production,protons must have energies in excess of 1016to 1018eV where abundant infrared photons can provide the target.Since the cross section for photo-pion produc-tion is relatively low,very high ambient photon densities are required to initiate the cascades.In this case,pair creation (γγ→e +e −),which has a much higher cross-section,must be important.The proton cascade models may well have a significant problems explaining the emission from objects like Mkn 421/501for this reason.FIG.3:Plot of TeVγ-rayflux versus X-rayflux measured with the HEGRA experiment during an intenseflare of Mrk501(courtesy Henric Krawczynski).In the PIC models[5]the proton-photon interaction occur with radio-IR photons in the jet.While a detailed analysis has not been published,Aharonian and others have pointed out that the required photon densities also imply large pair production optical depths,and may mean that the PIC models are not self-consistent. Models where the primary protons produce synchrotron radiation(and subsequent pair-cascades)may avoid this problem,but require even larger magneticfields[26].One advantage of the photon-pair cascade is that it produces a rather characteristic spectrum that does not depend sensitively on the model parameters.The detailed shape of this spectrum does not match some observations.Typically the spectra are too soft and overproduce X-rays,giving a spectrum that does not reproduce the strongly double-peaked spectrum observed.For the typical magneticfield values,the synchrotron spectrum is often too soft and lacks the spectral breaks that are observed.For these hadronic models to account for the double-peaked spectrum,the radio to X-ray emission is most likely produced by primary shock-accelerated electrons,while the gamma-ray emission is produced by energetic secondary electrons from the cascade.There is no natural explanation for the correlated variability in the two spectral bands,or in the correlation in the X-ray and gamma-ray cutoffenergy.To reach these energies on a sufficiently short timescale,the gyroradius must be limited to a compact region in the jet,the inverse-Compton emission must be suppressed,and magneticfields of up to40Gauss are required. The spectral variability seen in the X-ray waveband is consistent with much longer synchrotron cooling times than predicted by the hadronic models,and is quite consistent with magneticfields of a10to100mGauss. This is the same value of the magneticfield derived by a completely independent method within the framework of the synchrotron inverse-Compton model.The criticisms leveled at the electron models are that the magneticfields are too small compared with the value required for magnetic collimation of the jets,and that the required electron energies are too large to be explained by shock acceleration.Moreover,electron injection into shocks is poorly understood since the electron gyroradius is small compared to the proton gyroradius and presumably to the width of the broadened shock front.However we know that electrons are accelerated to100TeV energies in supernovae shocks,regardless of the theoretical difficulties in accounting for this observation.As will be shown below,if one accepts relatively large Doppler factors,a self-consistent explanation for the VHE gamma-ray emission can be derived from leptonic models.In the framework of either the EC or SSC models theγ-ray and X-ray data can be used to constrain the Doppler factorδ(this is thought to be close to the bulk Lorentz factor of the jet for blazars)and magneticfield B in the emission regions of Mrk421and Mrk501.The maximumγ-ray(IC)energy E C,max provides a lower limit on the maximum electron energy(with Lorentz factorγe,max)given byδγe,max>E C,max/m e c2;combining this with the measured cut-offenergy of the synchrotron emission E syn,max one obtains an upper limit on thelog n ,Hz -13-12-11-10-9-8l o g n F n ,e r g s -1c m -2FIG.4:Model fit to Mrk 421SED with both an SSC and external Compton component[20]magnetic field B <∼2×10−2E syn ,max δE −2C ,max (where E C ,max is in TeV).A lower limit on the magnetic fieldfollows from the requirement that the electron cooling time,t e ,cool ≈2×108δ−1γ−1e B −2s,must be less than theobserved flare decay timescale.These limits depend on the Doppler factor of the jet and in some cases cannot be satisfied unless δis significantly greater than unity [27,28].Typically,these arguments lead to predictions of ∼100mGauss fields and Doppler factors δ>10to 40for Mrk 421.Similar values for Mrk 501but typically with a reduced lower limit on the Doppler factor.Model fits (that ignore the fact that the multiwavelength data are not truly time-resolved)give similar values for the Doppler factor and magnetic field strength.For example,a simple one-zone model fit for Mrk 421,shown in Fig.4,only gives good fits for a Doppler factor approaching a value of δ≈100(as shown)[20].Doppler factors this large may present other problems.Radio observations of jets show radio components moving with velocities that imply bulk Lorentz factors Γ<∼10further out in the jet.If the jet is decelerated by the inverse-Compton scattering,most of the energy would be used up before such extended radio lobes could form in apparent contradiction to observations.Given the good progress to date,it appears that it will be possible to determine the dominant radiation processes in AGNs.After this first issue is resolved,further multiwavelength observations can address the more fundamental questions about the energetics of the central supermassive black hole,and the processes behind the formation of the relativistic jets.The very short variability timescales already observed with the Whipple instrument (15minute doubling times for Markarian 421)hint that the gamma-ray observations may be probing very close to the central engine,beyond the reach of the highest resolution optical and radio telescopes.B.Gamma-Ray BurstsGamma-ray bursts (GRBs)were discovered by the Vela satellites in the late 1960’s [29].GRBs are bright flashes of hard X-rays and low energy gamma rays coming from random directions in the sky at random times.Until the launch of the CGRO in 1992it was generally believed that GRBs were galactic phenomena associated with neutron stars.The BATSE instrument on-board the CGRO detected over 2000GRBs and the observed spatial distribution was isotropic,with no evidence of an excess from the galactic plane.Thus GRBs were either cosmological or populated an extended galactic halo.In 1997the BeppoSax satellite was launched.With a suite of hard X-ray detectors,this instrument has the ability to localize GRBs to within ∼1minute of arc [30](BATSE could localize GRBs to within ∼5degrees).The increased angular resolution allowed conventional ground-based telescopes to search the error box without significant source confusion.The observation of emission and absorption lines from the host galaxies led to measurements of redshifts;some thirty years after their discovery the cosmological nature of gamma-ray bursts was determined.In Figure II B we show the redshift distribution of those gamma-ray bursts where the redshift has been determined.The enormous energy output from GRBs,and transparency of the universe below 100MeV makes GRBs visible across the universe.Thus gamma-rayFIG.5:The magnitude redshift distribution of gamma-ray bursts.Also shown on the plot is the magnitude vs.redshift relation for the observed type Ia supernovae.bursts have the potential to probe the universe at very early times and to study the propagation of high-energy photons over cosmological distances.To use GRBs as cosmological probes it is necessary to understand their underlying mechanism.While GRBs may never be standard candles on par with the now famous Type-IA supernovae,there has been great progress made in the lastfive years in understanding GRBs.While we still do not know what the underlying energy source is,we are beginning to understand the environment that creates the observed high-energy photons. The large distances to GRBs implies that the energy released is∼1050−54ergs,depending on the amount of beaming at the source.While the origin of the initial explosion is unknown,the subsequent emission is well described by the relativisticfireball model.In this model shells of material expand relativistically into the interstellar medium.The complex gamma-ray light-curves of the prompt radiation arises from shocks formed as faster and slower shells of material interact.A termination shock is also formed as the expanding shells of material interact with the material surrounding the GRB progenitor.In this model the observed afterglows (x-ray,optical,and radio)arise from the synchrotron radiation of shock accelerated electrons.The afterglow emission can be used to determine the geometry of the source.Since the shell is expanding relativistically,the radiation(emitted isotropically in the bulk frame)is beamed into a cone with with opening angleΓ−1(the bulk Lorentz factor of the material in the shell).Thus at early times,only a small portion of the emitting surface is visible and one cannot distinguish between isotropic and beamed(jet-like)emission. However,as the shell expands it sweeps up material andΓdecreases.If the emission is not isotropic the beaming angle(Γ−1)will eventually become larger than the opening angle of the jet.At this point one should observe a break in the light curve(luminosity versus time)of the afterglow.This distinctive feature has been observed in15GRBs.By measuring the temporal breaks in GRBs of known redshift Frail et al.,[31]have measured the jet opening angles of15gamma-ray bursts(with some assumptions about the emission region:the jet is uniform across its face,the electron distribution in the shock is a power law,the afterglow radiation is due to synchrotron emission and inverse Compton scattering).If one integrates the observed luminosity over the inferred jet opening angle one can determine the intrinsic luminosity of each GRB.Surprisingly,Frail et al., conclude that the intrinsic luminosities of the observed gamma-ray bursts are peaked around5×1050ergs with a spread of roughly a factor of six.Thus the observed variation in luminosity(a factor of∼500)may be mainly due to the variation in the jet opening angle.Note that this conclusion applies only to the“long”GRBs,as these are the only GRBs for which optical counterparts have been observed.With a similar goal,to reduce the wide divergence in the observational properties of GRBs,Norris[32]has found a correlation between energy dependent time lags and the observed burst luminosity.Three things occur as one moves from high energy photons to low energy photons.The pulse profiles widen and become asymmetric, and the centroid of the pulse shifts to later times.The time lag is defined as the shift in the centroid of the pulse profile in the different energy channels of the BATSE instrument.In Figure II B we show the observed luminosity(assuming isotropic emission)versus the time lag observed between two energy channels on the BATSE experiment.(Channel1corresponds to photons with energies between25–50keV and channel3to 100300keV photons.)The line is the function,L53=1.1×(τlag/0.01s)−1.15,where L53is the luminosity in units of1053ergs.It may be that the time lag is dependent upon the jet opening angle for reasons that are not yet understood and this observed correlation is simply an way of paramterizing the relationship observed by Frail et al.As discussed above,gamma-ray observations of AGNs revealed a new spectral component due to inverse-Compton emission,distinct from the synchrotron emission observed in the radio to X-ray wavebands.This observation resulted in an independent constraint on the electron energy that allowed a determination of the magneticfields,electron densities,and bulk Lorentz factors in the sources.While AGNs are quite different for GRBs,the non-thermal radiation mechanisms may be quite similar,and we might expect similar progress to follow from high energy gamma-ray measurements.At higher energies less is known about GRBs.The EGRET instrument covered the energy range from100 MeV to a few tens of GeV.EGRET detected several GRBs at high energy(HE E>100MeV).From EGRET。

a r X i v :a s t r o -p h /9812370v 1 20 D e c 1998Constraining the IMF using TeV gamma rayabsorptionJ.S.Bullock a R.S.Somerville b D.MacMinn cand J.R.Primack aa PhysicsDepartment,University of California,Santa Cruz b RacahInstitute of Physics,Hebrew University,Jerusalemc Deceased 1Calculating the EBL and constraining the IMFSemi-analytic merging-tree (SAM)models of galaxy formation incorporate parameterized treatments of astrophysical processes such as gas cooling,star formation,supernovae feedback and dust absorption within the hierarchical structure formation ing the SAM models developed in Ref.[6],we can efficiently model the origin of the EBL in a variety of cosmological scenarios in a physical way.We can then use observations to contrain the nature of the IMF and the effects of dust (see [4,5]and [7],hereafter PBSM,for details).Fig.1.The attenuation factor forΛCDM models using a Salpeter(solid)and Scalo(dashed)IMF as a function of gamma ray energy Eγ,whereτ(Eγ)is the optical depth of the universe.The Salpeter IMF produces more high mass stars,thus more ultraviolet light and more∼100µm light reradiated by dust.For distant sources (redshift z s∼1)the Salpeter model’s increased UV light causes a noticeably larger attenuation of gamma rays.For nearby sources,the increase in reradiated light rel-ative to Scalo implies significantly increased gamma ray attenuation at Eγ>∼10TeV. In this contribution we focus on a model set in aflatΛCDM universe(Ωm= 0.4,ΩΛ=0.6),and investigate how the nature of the IMF affects the expected gamma-ray attenuation.We present results using two commonly used formsfor the IMF,Scalo[8]and Salpeter[9].Our results will primarily constrain the ratio of high mass to low mass stars produced.This quantity is of general interest in the context of understanding supernovae rates,metal production,and high redshift galaxies which are typically identified in the far UV.Note that there is some degeneracy between the effects of the IMF and the wave-length dependence of the dust extinction curve(see PBSM for a description of our treatment of dust).Figure1shows the gamma ray attenuation factor,exp(−τ),from ourΛCDM models using a Salpeter(solid)and Scalo(dashed)IMF.The optical depth isa function of gamma ray energy,τ(Eγ),and is most strongly influenced by the EBL at wavelengthsλEBL∼(Eγ/TeV)µm,where the cross section for pair production is maximized.The numbers next to each pair of curves indicatethe redshift of the source,z s.As discussed in detail in PBSM(seefigures2and4),the Salpeter IMF pro-duces more high mass stars,thus more ultraviolet light than does the ScaloIMF,and therefore a larger optical depth to<∼1TeV gamma rays.The increased UV light,in addition,produces more∼100µm light reradiated by dust,anda larger optical depth to>∼10TeV photons.Distant sources(z s>∼0.5)should provide an interesting probe of the IMF using<∼1TeV gamma ray telescopes. For nearby sources,the excess reradiated light relative to Scalo implies excess gamma ray attenuation at Eγ>∼10TeV,the relevant range for ground-based air-shower detectors.2ConclusionsGamma ray attenuation at Eγ<∼1TeV and>∼10TeV is significantly affected by the IMF,specifically the ratio of high to low mass stars,although there is some degeneracy associated with uncertainties in the modeling of dust absorption and reradiation.Observations of gamma ray absorption below∼1TeV for high redshift sources(z s>∼0.5)and above∼10TeV for nearby sources(z s∼0.03) will provide a useful probe of the nature of the IMF and galaxy formation.For more details,includingfitting functions of the optical depth of the universe as a function of redshift,cosmology,IMF,and gamma ray energy,see[4].References[1]R.J.Gould,G.P.Schr´e der,Phys.Rev.155(1967)1404.[2] F.W.Stecker,O.C.DeJager,M.H.Salamon,ApJ390(1992)L49;O.C.DeJager,F.W.Stecker,M.H.Salamon,Nature369(1994)294.[3] D.MacMinn,J.R.Primack Space Science Reviews75(1996)q413.[4]J.S.Bullock,R.S.Somerville, D.MacMinn,J.R.Primack in preparation(1998).[5]R.S.Somerville,J.S.Bullock,J.R.Primack,in preparation(1999).[6]R.S.Somerville,J.R.Primack MNRAS,accepted(1998).[7]J.R.Primack,J.S.Bullock,R.S.Somerville,D.MacMinn,these proceedings.[8]J.M.Scalo,Fundam.Cosmic Phys.11(1986)1.[9] E.E.Salpeter,ApJ121(1955)61.。

Detecting prompt gamma emission during proton therapy: the effects of detector size anddistance from the patient一项有关质子治疗中瞬发Gamma辐射的检测研究: 探测器大小的影响以及和病人间的距离本文章为德国慕尼黑质子治疗中心RPTC专项质子照射法临床效果研究, 目的是为了对一项在质子治疗中出现的瞬发Gamma辐射进行检测研究, 具体内容为探测器大小的影响以及与病人之间的距离Abstract摘要近期的研究显示, 在质子治疗中由活跃原子核而发出的瞬发Gamma射线(PGs)的特点有利于在导入性治疗之中用以确定波束的范围.由于PGs只有在束波照射时才会被发射出, 利用PGs来做在线治疗验证的可行性主要是要依赖高效探测器的设计.作为指导设计的方式和使用临床PG图像探测器, 本研究的目的是为了描述作为同病人之间距离函数的PG检测是如何地变化的.采用蒙特卡罗模型(GEANT4.9.4), 本研究涉及到一项对于全部PG 排放以及一项在质子照射内由(16)O产生的6.13MeVPG排放的高纯锗探测器的检测率(PGs每个射入的质子).作为从质子治疗喷嘴处ISO物理坐标中心的距离函数, PG探测率被做出了计算, 主要是针对: 采用质子笔型束照射的水幻象,一名采用扫描式质子束照射野的前列腺患者(横向照射野大小:∼6 cm × 6 cm, 束波范围23.5 cm)作为与ISO物理坐标中心位置间的距离函数, 探测器大小, 以及质子束能量, PG探测率的解析表达式被表现出来.对一项40MeV照射1水幻影的笔形束质子来说, 当探测器被放置在距中心11cm的位置上,探测率的数值分别为:A: 氧1.3 × 10(-6), 以及,B: 全部PG排放3.9 × 10(-4),对于超过150 MeV水平的束波能量, 全部的PG探测率则增加了∼85 ± 3%.对于氧和全部的PG排放指数来说, 在前列腺癌扫描式治疗中一项单一笔形束导入的过程内, 探测率大约呈2.1 × 10(-6)以及1.7 × 10(-3)的幅度.在对一水幻影采用单一质子笔形束的照射过程中, 作为自ISO物理坐标中心位置距离函数的PG探测率, 在通过常用于质子治疗束波能量范围下一点源模型照射一个已知直径的圆柱形探测器的方式, 被很好地描述了出来.对于患者的研究来说, 需要由一个指数因子来将点源方程做分离化的处理, 这样做是为了能正确地预测, 作为自ISO物理坐标中心位置的距离函数, PG检测率的下降趋势.。

第62卷第2期天文学报Vol.62No.2 2021年3月ACTA ASTRONOMICA SINICA Mar.,2021doi:10.15940/ki.0001-5245.2021.02.010博士学位论文摘要选登基于伽马射线的类轴子粒子探测及暗物质子晕搜寻研究夏子晴†(中国科学院紫金山天文台南京210023)目前已经有很多观测证据表明宇宙中存在着大量暗物质,其能量密度占据了目前宇宙总能量密度的1/4.根据高精度的数值模拟和引力透镜观测,我们已经对从矮星系到星系团中的暗物质空间分布有了较好的理解,但是对于暗物质究竟是什么我们还一无所知.由此,物理学家提出了很多假想的粒子模型.其中比较著名的粒子模型有:弱相互作用大质量粒子(WIMP)、轴子和类轴子(ALP).弱相互作用大质量粒子只存在弱相互作用和引力相互作用,可以相互湮灭(或者衰变)成稳定的高能粒子,包括伽马光子、带电粒子和中微子.从而使我们可以通过探测其湮灭(或者衰变)产生的高能粒子来间接探测弱相互作用大质量粒子.ALP可以在电磁场中与光子相互转化,这一特性使得我们可以通过寻找伽马射线能谱中的光子-类轴子振荡结构来间接探测类轴子.本文中的研究主要是利用公开的费米大面积望远镜(Fermi Large Area Telescope,Fermi-LAT)的数据和已发表的大气切伦科夫望远镜High Energy Stereoscopic System(H.E.S.S.)能谱数据,对暗物质粒子(轴子和类轴子、弱相互作用大质量粒子)进行间接探测.银河系中广泛存在着磁场,因此在河内源的能谱中可能存在着由光子和类轴子相互转化而形成的振荡结构.首先我们选取了3个在银盘上且非常明亮的超新星遗迹作为目标源(分别是IC443、W44和W51C),利用Fermi-LAT对这3个超新星遗迹的观测来寻找光子-类轴子振荡信号.在IC443的能谱中,我们找到了疑似的振荡结构,但是其对应的类轴子参数空间已经被太阳轴子望远镜CAST(CERN(European Centre for Nuclear Research)Axion Solar Telescope)排除.我们猜测,由于IC443是个空间延展的源,其能谱中出现的疑似的振荡结构可能是来自不同区域伽马射线辐射叠加的结果.然后我们选取了10个明亮的位于银盘上的TeV源,利用H.E.S.S.发表的能谱数据继续搜寻类轴子.然而我们并没有找到明显的光子-类轴子振荡信号,随后计算出了对类轴子参数空间的限制.这是首次利用天文观测数据在高质量区域(100neV)对解释河外TeV伽马射线反常弱吸收的类轴子模型参数空间进行排除.我们还利用Fermi-LAT伽马射线观测,搜寻了来自暗物质子晕结构的弱相互作用大质量粒子湮灭信号.目前有大量数值模拟的结果显示,像银河系这样的星系中存在大量的暗物质子晕结构.暗物质粒子可以湮灭或者衰变产生伽马射线.因此质量足够大且距我们足够近的暗物质子晕可能会以稳定延展伽马射线源的形式出现,同时没有其他波段的对应天体.以此为标准,我们找到了一个可能的暗物质子晕候选体3FGL J1924.8−1034,但是由于Fermi-LAT角分辨率的局限,我们不能排除它是由两个(及以上)邻近点源组成的可能.由于高的质光比,矮椭球星系一直被认为是暗物质间接探测的理想目标.我们搜寻了银河系附近矮椭球星系的伽马射线辐射,来探测弱相互作用大质量粒子的信号.分析发现来自Reticulum II方向的伽马射线信号是随时间稳步增长的.随后我们对所有目标源进行了联合分析,得到的联合伽马射线信†2019-06-20获得博士学位,导师:紫金山天文台伍健研究员和范一中研究员;21-12天文学报62卷号已经超过了4σ的局域置信度.在暗物质间接探测中,主要困难在于如何把暗物质湮灭或衰变产物的信号从天体物理背景中分离出来.如果是搜寻具有某些独特特征的能谱,如线谱和箱型能谱,在这方面遇到的困难就要小一些,因为通常的天体物理辐射过程难以出现这种特殊结构的能谱.在本文的工作中,我们还利用了Fermi-LAT数据来搜寻暗物质粒子可能产生的特征能谱(包括线谱和箱型能谱)信号.我们分别在银河系卫星星系和银河系内的暗物质子晕结构(通过N体模拟)寻找潜在的线谱信号.由于没有发现明显信号,我们随后计算出了暗物质湮灭成两个光子的湮灭截面的相应上限.随后我们还在矮椭球星系中,研究了由暗物质湮灭或衰变所产生的中间粒子衰变发出的箱型伽马射线能谱信号.Probe Axion-like Particles(ALPs)and Search for Dark Matter Subhalo with the Gamma-rayObservationsXIA Zi-qing(Purple Mountain Observatory,Chinese Academy of Sciences,Nanjing210023)The presence of a large amount of dark matter(DM)in the Universe has already been convincingly established.DM is believed to make up a quarter of the energy density of the current Universe.Thanks to high-resolution numerical simulations made possible by modern supercomputers and the gravitational lensing observations,the distribution of DM in structures ranging from dwarf galaxies to clusters of galaxies has been understood better than before.But the nature of DM remains unknown.Various hypothetical particles have been proposed,such as weakly-interacting mas-sive particles(WIMPs),axion,axion-like particles(ALPs),sterile neutrino and gravitino. WIMPs may be able to annihilate with each other(or alternatively decay)into stable high-energy particle pairs,including gamma-rays,charged particles and neutrinos.ALPs and photons can convert to each other in electromagneticfields through the Primakoffprocess, which could result in the detectable spectral oscillation phenomena in the gamma-rays ob-servation.My research mainly focused on the indirect detection of dark matter,such as ALPs and WIMPs,using publicly available Fermi Large Area Telescope(Fermi-LAT)data and the the published data of High Energy Stereoscopic System(H.E.S.S.)observation.The conversion between photons and ALPs in the Milky Way magneticfield could result in the detectable oscillation phenomena in the gamma-ray spectra of the Galactic sources. First,we search for such oscillation effects in the spectra of supernova remnants caused by the photon-ALP conversion,using the Fermi LAT data.The inclusion of photon-ALP oscillations yields an improvedfit to theγ-ray spectrum of IC443,which gives a statistical significance of4.2σin favor of such spectral oscillation.However,the best-fit parameters of ALPs are in tension with the CAST(CERN(European Centre for Nuclear Research)Axion Solar Telescope)limits.Secondly,we use the H.E.S.S.observations of some TeV sources in the Galactic plane to exclude the highest ALP mass region(i.e.,ALP mass m a∼10−7eV) that accounts for the anomalously weak absorption of TeV gamma-rays for thefirst time.A Milky Way-like galaxy is predicted to host tens of thousands of galactic DM subhalos. Annihilation of WIMPs in massive and nearby subhalos could generate detectable gamma-rays,appearing as unidentified,spatially-extended and stable gamma-ray sources.We search for such sources in the third Fermi Large Area Telescope source List(3FGL)and report21-22期夏子晴:基于伽马射线的类轴子粒子探测及暗物质子晕搜寻研究3the identification of a new candidate,3FGL J1924.8−1034.3FGL J1924.8−1034is found spatially-extended at a high confidence level of5.4σ.No significant variability has been found and its gamma-ray spectrum is wellfitted by the dark matter annihilation into b¯b with a mass of∼43GeV.All these facts make3FGL J1924.8−1034a possible dark matter subhalo candidate.However,due to the limited angular resolution,the possibility that the spatial extension of3FGL J1924.8−1034is caused by the contamination from the other un-resolved point source can not be ruled out.The Milky Way dwarf spheroidal galaxy is considered one of the most ideal targets for indirect detection of dark matter due to their high dark matter density and low astrophysical backgrounds.We search for gamma-ray emission from nearby Milky Way dwarf spheroidal galaxies and candidates with Fermi-LAT data.Intriguingly,the peak TS(Test Statistic) value of the weak emission from Reticulum II rises continually.We alsofind that the combination of all these nearby sources will result in a more significant(>4σ)gamma-ray signal.A commonly encountered obstacle in indirect searches for dark matter is how to disentangle possible signals from astrophysical backgrounds.Gamma-ray features,in particular monochromatic gamma-ray lines and boxlike spectral features,provide smoking gun signatures.We analyze the Fermi LAT observation of Milky Way satellites and the local volume dark matter subhalo population(with N-body simulation)to search for potential line signals,respectively.The corresponding upper limits on the cross section of DM annihilation into two photons are derived,without significant signal found.Then we study the box-shaped DM signals,which is generated by the decay of intermediate particles produced by DM annihilation or decay,with Fermi-LAT observations of dwarf spheroidal galaxies.21-3。

Proton range verification through prompt gamma-ray spectroscopy一项有关通过瞬发Gamma射线光谱的质子范围验证效果评估本文章为德国慕尼黑质子治疗中心RPTC专项质子照射法临床效果研究, 目的是为了评估一项通过瞬发Gamma射线光谱的质子范围验证实际效果Abstract摘要本研究是一项针对采用新颖手法验证质子束照射法范围的实验性研究.在上至150MeV的质子能量水平下, 对15项带有C(12)和O(16)条件的来自质子--核子交互作用瞬间Gamma射线的不同微分截面被一一进行了测量.这些截面被用来模仿沿质子笔形束而出现的离散性瞬发Gamma射线的辐射效应.通过使得被侦测到的Gamma射线与这些模型相匹配, 本研究即时性地确定了照射波束的范围以及照射物体的氧与碳的浓度程度.本方法在两个带有不同元素浓度的幻影中被进行了评估, 采用了一个小型规模的原型探测器.依照带有不同范围的导入5x10(8)的5项笔型束质子, 以及在预先不了解元素组成测量点的情况下, 绝对范围在标准差为1.0-1.4mm内被测定出.相同剂量水平下的相对范围转换值被侦测到, 标准差达到了0.3-0.5mm.确定出的氧和碳的浓度程度也与实际值保持了一致性.以上这些结果显示出, 定量性质的瞬间Gamma射线测量值可以使得对核反应截面的知识,在带有未知成分的组织中, 作为精确质子验证范围而得以应用.在有关质子照射束波如何能够对不同癌症和肿瘤进行治疗时, 来自中国大陆的北京携康长荣医院管理有限公司顾欣董事长有着独到的见解. 他指出, 质子特有的物理效应可以使得患者在接受照射时不会受到剂量导出的辐射危害, 在打击肿瘤的同时避免了对正常组织的免伤化效果, 这样的做法可以精确地对肿瘤病灶进行照射, 提高了治疗的有效性.。