A Gamma-Ray Burst Bibliography, 1973

Designation:E94–04Standard Guide forRadiographic Examination1This standard is issued under thefixed designation E94;the number immediately following the designation indicates the year of original adoption or,in the case of revision,the year of last revision.A number in parentheses indicates the year of last reapproval.A superscript epsilon(e)indicates an editorial change since the last revision or reapproval.1.Scope1.1This guide2covers satisfactory X-ray and gamma-ray radiographic examination as applied to industrial radiographic film recording.It includes statements about preferred practice without discussing the technical background which justifies the preference.A bibliography of several textbooks and standard documents of other societies is included for additional infor-mation on the subject.1.2This guide covers types of materials to be examined; radiographic examination techniques and production methods; radiographicfilm selection,processing,viewing,and storage; maintenance of inspection records;and a list of available reference radiograph documents.N OTE1—Further information is contained in Guide E999,Practice E1025,Test Methods E1030and E1032.1.3Interpretation and Acceptance Standards—Interpretation and acceptance standards are not covered by this guide,beyond listing the available reference radiograph docu-ments for castings and welds.Designation of accept-reject standards is recognized to be within the cognizance of product specifications and generally a matter of contractual agreement between producer and purchaser.1.4Safety Practices—Problems of personnel protection against X rays and gamma rays are not covered by this document.For information on this important aspect of radiog-raphy,reference should be made to the current document of the National Committee on Radiation Protection and Measure-ment,Federal Register,U.S.Energy Research and Develop-ment Administration,National Bureau of Standards,and to state and local regulations,if such exist.For specific radiation safety information refer to NIST Handbook ANSI43.3,21 CFR1020.40,and29CFR1910.1096or state regulations for agreement states.1.5This standard does not purport to address all of the safety problems,if any,associated with its use.It is the responsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.(See1.4.)1.6If an NDT agency is used,the agency shall be qualified in accordance with Practice E543.2.Referenced Documents2.1ASTM Standards:3E543Practice for Evaluating Agencies that Perform Non-destructive TestingE746Test Method for Determining Relative Image Quality Response of Industrial Radiographic Film SystemsE747Practice for Design,Manufacture,and Material Grouping Classification of Wire Image Quality Indicators (IQI)Used for RadiologyE801Practice for Controlling Quality of Radiological Ex-amination of Electronic DevicesE999Guide for Controlling the Quality of Industrial Ra-diographic Film ProcessingE1025Practice for Design,Manufacture,and Material Grouping Classification of Hole-Type Image Quality Indi-cators(IQI)Used for RadiologyE1030Test Method for Radiographic Examination of Me-tallic CastingsE1032Test Method for Radiographic Examination of WeldmentsE1079Practice for Calibration of Transmission Densitom-etersE1254Guide for Storage of Radiographs and Unexposed Industrial Radiographic FilmsE1316Terminology for Nondestructive ExaminationsE1390Guide for Illuminators Used for Viewing Industrial RadiographsE1735Test Method for Determining Relative Image Qual-ity of Industrial Radiographic Film Exposed to X-Radiation from4to25MVE1742Practice for Radiographic ExaminationE1815Test Method for Classification of Film Systems for Industrial Radiography2.2ANSI Standards:1This guide is under the jurisdiction of ASTM Committee E07on Nondestruc-tive Testing and is the direct responsibility of Subcommittee E07.01on Radiology (X and Gamma)Method.Current edition approved January1,2004.Published February2004.Originally approved st previous edition approved in2000as E94-00.2For ASME Boiler and Pressure Vessel Code applications see related Guide SE-94in Section V of that Code.3For referenced ASTM standards,visit the ASTM website,,or contact ASTM Customer Service at service@.For Annual Book of ASTM Standards volume information,refer to the standard’s Document Summary page on the ASTM website.Copyright©ASTM International,100Barr Harbor Drive,PO Box C700,West Conshohocken,PA19428-2959,United States.PH1.41Specifications for Photographic Film for Archival Records,Silver-Gelatin Type,on Polyester Base 4PH2.22Methods for Determining Safety Times of Photo-graphic Darkroom Illumination 4PH4.8Methylene Blue Method for Measuring Thiosulfate and Silver Densitometric Method for Measuring Residual Chemicals in Films,Plates,and Papers 4T9.1Imaging Media (Film)—Silver-Gelatin Type Specifi-cations for Stability 4T9.2Imaging Media—Photographic Process Film Plate and Paper Filing Enclosures and Storage Containers 42.3Federal Standards:Title 21,Code of Federal Regulations (CFR)1020.40,Safety Requirements of Cabinet X-Ray Systems 5Title 29,Code of Federal Regulations (CFR)1910.96,Ionizing Radiation (X-Rays,RF,etc.)52.4Other Document:NBS Handbook ANSI N43.3General Radiation Safety Installations Using NonMedical X-Ray and Sealed Gamma Sources up to 10MeV 63.Terminology3.1Definitions —For definitions of terms used in this guide,refer to Terminology E 1316.4.Significance and Use4.1Within the present state of the radiographic art,this guide is generally applicable to available materials,processes,and techniques where industrial radiographic films are used as the recording media.4.2Limitations —This guide does not take into consider-ation special benefits and limitations resulting from the use of nonfilm recording media or readouts such as paper,tapes,xeroradiography,fluoroscopy,and electronic image intensifi-cation devices.Although reference is made to documents that may be used in the identification and grading,where appli-cable,of representative discontinuities in common metal cast-ings and welds,no attempt has been made to set standards of acceptance for any material or production process.Radiogra-phy will be consistent in sensitivity and resolution only if the effect of all details of techniques,such as geometry,film,filtration,viewing,etc.,is obtained and maintained.5.Quality of Radiographs5.1To obtain quality radiographs,it is necessary to consider as a minimum the following list of items.Detailed information on each item is further described in this guide.5.1.1Radiation source (X-ray or gamma),5.1.2V oltage selection (X-ray),5.1.3Source size (X-ray or gamma),5.1.4Ways and means to eliminate scattered radiation,5.1.5Film system class,5.1.6Source to film distance,5.1.7Image quality indicators (IQI’s),5.1.8Screens and filters,5.1.9Geometry of part or component configuration,5.1.10Identification and location markers,and 5.1.11Radiographic quality level.6.Radiographic Quality Level6.1Information on the design and manufacture of image quality indicators (IQI’s)can be found in Practices E 747,E 801,E 1025,and E 1742.6.2The quality level usually required for radiography is 2%(2-2T when using hole type IQI)unless a higher or lower quality is agreed upon between the purchaser and the supplier.At the 2%subject contrast level,three quality levels of inspection,2-1T,2-2T,and 2-4T,are available through the design and application of the IQI (Practice E 1025,Table 1).Other levels of inspection are available in Practice E 1025Table 1.The level of inspection specified should be based on the service requirements of the product.Great care should be taken in specifying quality levels 2-1T,1-1T,and 1-2T by first determining that these quality levels can be maintained in production radiography.N OTE 2—The first number of the quality level designation refers to IQI thickness expressed as a percentage of specimen thickness;the second number refers to the diameter of the IQI hole that must be visible on the radiograph,expressed as a multiple of penetrameter thickness,T .6.3If IQI’s of material radiographically similar to that being examined are not available,IQI’s of the required dimensions but of a lower-absorption material may be used.6.4The quality level required using wire IQI’s shall be equivalent to the 2-2T level of Practice E 1025unless a higher or lower quality level is agreed upon between purchaser and supplier.Table 4of Practice E 747gives a list of various hole-type IQI’s and the diameter of the wires of corresponding EPS with the applicable 1T,2T,and 4T holes in the plaque IQI.Appendix X1of Practice E 747gives the equation for calcu-lating other equivalencies,if needed.7.Energy Selection7.1X-ray energy affects image quality.In general,the lower the energy of the source utilized the higher the achievable radiographic contrast,however,other variables such as geom-etry and scatter conditions may override the potential advan-tage of higher contrast.For a particular energy,a range of thicknesses which are a multiple of the half value layer,may be radiographed to an acceptable quality level utilizing a particu-lar X-ray machine or gamma ray source.In all cases the specified IQI (penetrameter)quality level must be shown on the radiograph.In general,satisfactory results can normally be obtained for X-ray energies between 100kV to 500kV in a range between 2.5to 10half value layers (HVL)of material thickness (see Table 1).This range may be extended by as much as a factor of 2in some situations for X-ray energies in the 1to 25MV range primarily because of reduced scatter.4Available from American National Standards Institute (ANSI),25W.43rd St.,4th Floor,New York,NY 10036.5Available from ernment Printing Office Superintendent of Documents,732N.Capitol St.,NW,Mail Stop:SDE,Washington,DC 20401.6Available from National Technical Information Service (NTIS),U.S.Depart-ment of Commerce,5285Port Royal Rd.,Springfield,V A22161.8.Radiographic Equivalence Factors8.1The radiographic equivalence factor of a material is that factor by which the thickness of the material must be multi-plied to give the thickness of a “standard”material (often steel)which has the same absorption.Radiographic equivalence factors of several of the more common metals are given in Table 2,with steel arbitrarily assigned a factor of 1.0.The factors may be used:8.1.1To determine the practical thickness limits for radia-tion sources for materials other than steel,and8.1.2To determine exposure factors for one metal from exposure techniques for other metals.9.Film9.1Various industrial radiographic film are available to meet the needs of production radiographic work.However,definite rules on the selection of film are difficult to formulate because the choice depends on individual user requirements.Some user requirements are as follows:radiographic quality levels,exposure times,and various cost factors.Several methods are available for assessing image quality levels (see Test Method E 746,and Practices E 747and E 801).Informa-tion about specific products can be obtained from the manu-facturers.9.2Various industrial radiographic films are manufactured to meet quality level and production needs.Test Method E 1815provides a method for film manufacturer classification of film systems.A film system consist of the film andassociated film processing ers may obtain a classi-fication table from the film manufacturer for the film system used in production radiography.A choice of film class can be made as provided in Test Method E 1815.Additional specific details regarding classification of film systems is provided in Test Method E 1815.ANSI Standards PH1.41,PH4.8,T9.1,and T9.2provide specific details and requirements for film manufacturing.10.Filters10.1Definition —Filters are uniform layers of material placed between the radiation source and the film.10.2Purpose —The purpose of filters is to absorb the softer components of the primary radiation,thus resulting in one or several of the following practical advantages:10.2.1Decreasing scattered radiation,thus increasing con-trast.10.2.2Decreasing undercutting,thus increasing contrast.10.2.3Decreasing contrast of parts of varying thickness.10.3Location —Usually the filter will be placed in one of the following two locations:10.3.1As close as possible to the radiation source,which minimizes the size of the filter and also the contribution of the filter itself to scattered radiation to the film.10.3.2Between the specimen and the film in order to absorb preferentially the scattered radiation from the specimen.It should be noted that lead foil and other metallic screens (see 13.1)fulfill this function.10.4Thickness and Filter Material —The thickness and material of the filter will vary depending upon the following:10.4.1The material radiographed.10.4.2Thickness of the material radiographed.10.4.3Variation of thickness of the material radiographed.10.4.4Energy spectrum of the radiation used.10.4.5The improvement desired (increasing or decreasing contrast).Filter thickness and material can be calculated or determined empirically.11.Masking11.1Masking or blocking (surrounding specimens or cov-ering thin sections with an absorptive material)is helpful in reducing scattered radiation.Such a material can also be usedTABLE 1Typical Steel HVL Thickness in Inches [mm]forCommon EnergiesEnergyThickness,Inches [mm]120kV 0.10[2.5]150kV 0.14[3.6]200kV 0.20[5.1]250kV0.25[6.4]400kV (Ir 192)0.35[8.9]1MV0.57[14.5]2MV (Co 60)0.80[20.3]4MV 1.00[25.4]6MV 1.15[29.2]10MV1.25[31.8]16MV and higher1.30[33.0]TABLE 2Approximate Radiographic Equivalence Factors for Several Metals (Relative to Steel)MetalEnergy Level100kV 150kV 220kV 250kV400kV1MV2MV4to 25MV192Ir60CoMagnesium 0.050.050.08Aluminum0.080.120.180.350.35Aluminum alloy 0.100.140.180.350.35Titanium0.540.540.710.90.90.90.90.9Iron/all steels 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0Copper 1.51.6 1.4 1.41.4 1.1 1.1 1.2 1.1 1.1Zinc 1.4 1.3 1.3 1.2 1.1 1.0Brass 1.4 1.3 1.3 1.2 1.1 1.0 1.1 1.0Inconel X 1.4 1.3 1.3 1.3 1.3 1.3 1.3 1.3Monel 1.7 1.2Zirconium2.4 2.3 2.0 1.7 1.5 1.0 1.0 1.0 1.2 1.0Lead 14.014.012.0 5.0 2.52.7 4.0 2.3Hafnium 14.012.09.03.0Uranium20.016.012.04.03.912.63.4to equalize the absorption of different sections,but the loss of detail may be high in the thinner sections.12.Back-Scatter Protection12.1Effects of back-scattered radiation can be reduced by confining the radiation beam to the smallest practical cross section and by placing lead behind thefilm.In some cases either or both the back lead screen and the lead contained in the back of the cassette orfilm holder will furnish adequate protection against back-scattered radiation.In other instances, this must be supplemented by additional lead shielding behind the cassette orfilm holder.12.2If there is any question about the adequacy of protec-tion from back-scattered radiation,a characteristic symbol (frequently a1⁄8-in.[3.2-mm]thick letter B)should be attached to the back of the cassette orfilm holder,and a radiograph made in the normal manner.If the image of this symbol appears on the radiograph as a lighter density than background, it is an indication that protection against back-scattered radia-tion is insufficient and that additional precautions must be taken.13.Screens13.1Metallic Foil Screens:13.1.1Lead foil screens are commonly used in direct contact with thefilms,and,depending upon their thickness, and composition of the specimen material,will exhibit an intensifying action at as low as90kV.In addition,any screen used in front of thefilm acts as afilter(Section10)to preferentially absorb scattered radiation arising from the speci-men,thus improving radiographic quality.The selection of lead screen thickness,or for that matter,any metallic screen thickness,is subject to the same considerations as outlined in 10.4.Lead screens lessen the scatter reaching thefilm regard-less of whether the screens permit a decrease or necessitate an increase in the radiographic exposure.To avoid image unsharp-ness due to screens,there should be intimate contact between the lead screen and thefilm during exposure.13.1.2Lead foil screens of appropriate thickness should be used whenever they improve radiographic quality or penetram-eter sensitivity or both.The thickness of the front lead screens should be selected with care to avoid excessivefiltration in the radiography of thin or light alloy materials,particularly at the lower kilovoltages.In general,there is no exposure advantage to the use of0.005in.in front and back lead screens below125 kV in the radiography of1⁄4-in.[6.35-mm]or lesser thickness steel.As the kilovoltage is increased to penetrate thicker sections of steel,however,there is a significant exposure advantage.In addition to intensifying action,the back lead screens are used as protection against back-scattered radiation (see Section12)and their thickness is only important for this function.As exposure energy is increased to penetrate greater thicknesses of a given subject material,it is customary to increase lead screen thickness.For radiography using radioac-tive sources,the minimum thickness of the front lead screen should be0.005in.[0.13mm]for iridium-192,and0.010in.[0.25mm]for cobalt-60.13.2Other Metallic Screen Materials:13.2.1Lead oxide screens perform in a similar manner to lead foil screens except that their equivalence in lead foil thickness approximates0.0005in.[0.013mm].13.2.2Copper screens have somewhat less absorption and intensification than lead screens,but may provide somewhat better radiographic sensitivity with higher energy above1MV.13.2.3Gold,tantalum,or other heavy metal screens may be used in cases where lead cannot be used.13.3Fluorescent Screens—Fluorescent screens may be used as required providing the required image quality is achieved.Proper selection of thefluorescent screen is required to minimize image unsharpness.Technical information about specificfluorescent screen products can be obtained from the manufacturers.Goodfilm-screen contact and screen cleanli-ness are required for successful use offluorescent screens. Additional information on the use offluorescent screens is provided in Appendix X1.13.4Screen Care—All screens should be handled carefully to avoid dents and scratches,dirt,or grease on active surfaces. Grease and lint may be removed from lead screens with a solvent.Fluorescent screens should be cleaned in accordance with the recommendations of the manufacturer.Screens show-ing evidence of physical damage should be discarded.14.Radiographic Image Quality14.1Radiographic image quality is a qualitative term used to describe the capability of a radiograph to showflaws in the area under examination.There are three fundamental compo-nents of radiographic image quality as shown in Fig.1.Each component is an important attribute when considering a specific radiographic technique or application and will be briefly discussed below.14.2Radiographic contrast between two areas of a radio-graph is the difference between thefilm densities of those areas.The degree of radiographic contrast is dependent upon both subject contrast andfilm contrast as illustrated in Fig.1.14.2.1Subject contrast is the ratio of X-ray or gamma-ray intensities transmitted by two selected portions of a specimen. Subject contrast is dependent upon the nature of the specimen (material type and thickness),the energy(spectral composition, hardness or wavelengths)of the radiation used and the intensity and distribution of scattered radiation.It is independent of time,milliamperage or source strength(curies),source distance and the characteristics of thefilm system.14.2.2Film contrast refers to the slope(steepness)of the film system characteristic curve.Film contrast is dependent upon the type offilm,the processing it receives and the amount offilm density.It also depends upon whether thefilm was exposed with lead screens(or without)or withfluorescent screens.Film contrast is independent,for most practical purposes,of the wavelength and distribution of the radiation reaching thefilm and,hence is independent of subject contrast. For further information,consult Test Method E1815.14.3Film system granularity is the objective measurement of the local density variations that produce the sensation of graininess on the radiographicfilm(for example,measured with a densitometer with a small aperture of#0.0039in.[0.1 mm]).Graininess is the subjective perception of a mottled random pattern apparent to a viewer who sees smalllocaldensity variations in an area of overall uniform density (that is,the visual impression of irregularity of silver deposit in a processed radiograph).The degree of granularity will not affect the overall spatial radiographic resolution (expressed in line pairs per mm,etc.)of the resultant image and is usually independent of exposure geometry arrangements.Granularity is affected by the applied screens,screen-film contact and film processing conditions.For further information on detailed perceptibility,consult Test Method E 1815.14.4Radiographic definition refers to the sharpness of the image (both the image outline as well as image detail).Radiographic definition is dependent upon the inherent un-sharpness of the film system and the geometry of the radio-graphic exposure arrangement (geometric unsharpness)as illustrated in Fig.1.14.4.1Inherent unsharpness (U i )is the degree of visible detail resulting from geometrical aspects within the film-screen system,that is,screen-film contact,screen thickness,total thickness of the film emulsions,whether single or double-coated emulsions,quality of radiation used (wavelengths,etc.)and the type of screen.Inherent unsharpness is independent of exposure geometry arrangements.14.4.2Geometric unsharpness (U g )determines the degree of visible detail resultant from an “in-focus”exposure arrange-ment consisting of the source-to-film-distance,object-to-film-distance and focal spot size.Fig.2(a)illustrates these condi-tions.Geometric unsharpness is given by the equation:U g 5Ft /d o(1)where:U g =geometric unsharpness,F =maximum projected dimension of radiation source,t =distance from source side of specimen to film,and d o =source-object distance.N OTE 3—d o and t must be in the same units of measure;the units of U g will be in the same units as F .N OTE 4—A nomogram for the determination of U g is given in Fig.3(inch-pound units).Fig.4represents a nomogram in metric units.Example:Given:Source-object distance (d o )=40in.,Source size (F)=500mils,andSource side of specimen to film distance (t)=1.5in.Draw a straight line (dashed in Fig.3)between 500mils on the F scale and 1.5in.on the t scale.Note the point on intersection (P)of this line with the pivot line.Draw a straight line (solid in Fig.3)from 40in.on the d o scale through point P and extend to the U g scale.Intersection of this line with the U g scale gives geometrical unsharpness in mils,which in the example is 19mils.Inasmuch as the source size,F ,is usually fixed for a given radiation source,the value of U g is essentially controlled by the simple d o /t ratio.Geometric unsharpness (U g )can have a significant effect on the quality of the radiograph;therefore source-to-film-distance (SFD)selection is important.The geometric unsharpness (U g )equation,Eq 1,is for information and guidance and provides a means for determining geometric unsharpness values.The amount or degree of unsharpness should be minimized when establishing the radiographic technique.Radiographic Image QualityRadiographic ContrastFilm System Granularity Radiographic DefinitionSubject Contrast Film Contrast •Grain size and distribution within the film emulsion •Processing conditions(type and activity of developer,temperature of developer,etc.)•Type ofscreens (that is,fluorescent,lead or none)•Radiation quality (that is,energy level,filtration,etc.•Exposure quanta (that is,intensity,dose,etc.)InherentUnsharpness Geometric Unsharpness Affected by:•Absorption differences in specimen (thickness,composition,density)•Radiation wavelength •Scattered radiationAffected by:•Type of film•Degree of development (type of developer,time,temperature and activity of developer,degree of agitation)•Film density •Type ofscreens (that is,fluorescent,lead or none)Affected by:•Degree of screen-film contact •Total film thickness •Single ordouble emulsion coatings •Radiation quality •Type and thickness of screens (fluorescent,lead or none)Affected by:•Focal spot or source physical size •Source-to-film distance •Specimen-to-film distance•Abruptness of thickness changes in specimen •Motion of specimen or radiation sourceReduced or enhanced by:•Masks and diaphragms •Filters•Lead screens •Potter-Bucky diaphragmsFIG.1Variables of Radiographic ImageQualityFIG.2Effects of Object-Film Geometry15.Radiographic Distortion15.1The radiographic image of an object or feature within an object may be larger or smaller than the object or feature itself,because the penumbra of the shadow is rarely visible in a radiograph.Therefore,the image will be larger if the object or feature is larger than the source of radiation,and smaller if object or feature is smaller than the source.The degree of reduction or enlargement will depend on the source-to-object and object-to-film distances,and on the relative sizes of the source and the object or feature (Fig.2(b )and (c )).15.2The direction of the central beam of radiation should be perpendicular to the surface of the film whenever possible.The object image will be distorted if the film is not aligned perpendicular to the central beam.Different parts of the object image will be distorted different amount depending on the extent of the film to central beam offset (Fig.2(d )).16.Exposure Calculations or Charts16.1Development or procurement of an exposure chart or calculator is the responsibility of the individual laboratory.16.2The essential elements of an exposure chart or calcu-lator must relate the following:16.2.1Source or machine,16.2.2Material type,16.2.3Material thickness,16.2.4Film type (relative speed),16.2.5Film density,(see Note 5),16.2.6Source or source to film distance,16.2.7Kilovoltage or isotope type,N OTE 5—For detailed information on film density and density measure-ment calibration,see Practice E 1079.16.2.8Screen type andthickness,FIG.3Nomogram for Determining Geometrical Unsharpness (Inch-PoundUnits)16.2.9Curies or milliampere/minutes,16.2.10Time of exposure,16.2.11Filter (in the primary beam),16.2.12Time-temperature development for hand process-ing;access time for automatic processing;time-temperature development for dry processing,and16.2.13Processing chemistry brand name,if applicable.16.3The essential elements listed in 16.2will be accurate for isotopes of the same type,but will vary with X-ray equipment of the same kilovoltage and milliampere rating.16.4Exposure charts should be developed for each X-ray machine and corrected each time a major component is replaced,such as the X-ray tube or high-voltage transformer.16.5The exposure chart should be corrected when the processing chemicals are changed to a different manufacturer’s brand or the time-temperature relationship of the processormay be adjusted to suit the exposure chart.The exposure chart,when using a dry processing method,should be corrected based upon the time-temperature changes of the processor.17.Technique File17.1It is recommended that a radiographic technique log or record containing the essential elements be maintained.17.2The radiographic technique log or record should con-tain the following:17.2.1Description,photo,or sketch of the test object illustrating marker layout,source placement,and film location.17.2.2Material type and thickness,17.2.3Source to film distance,17.2.4Film type,17.2.5Film density,(see Note 5),17.2.6Screen type andthickness,FIG.4Nomogram for Determining Geometrical Unsharpness (MetricUnits)。

a r X i v :a s t r o -p h /0111030v 1 1 N o v 2001Gamma Ray Bursts as Probes of the First StarsJames E.RhoadsSTScI,3700San Martin Dr.,Baltimore,MD 21210,USAAbstract.The redshift where the first stars formed is an important and unknown milestone in cos-mological structure formation.The evidence linking gamma ray bursts (GRBs)with star formation activity implies that the first GRBs occurred shortly after the first stars formed.Gamma ray bursts and their afterglows may thus offer a unique probe of this epoch,because they are bright from gamma ray to radio wavelengths and should be observable to very high redshift.Indeed,our on-going near-IR followup programs already have the potential to detect bursts at redshift z ∼10.In these proceedings,we discuss two distinct ways of using GRBs to probe the earliest star formation.First,direct GRB counts may be used as a proxy for star formation rate measurements.Second,high energy cutoffs in the GeV spectra of gamma ray bursts due to pair production with high redshift op-tical and ultraviolet background photons contain information on early star formation history.The second method is observationally more demanding,but also more rewarding,because each observed pair creation cutoff in a high redshift GRB spectrum will tell us about the integrated star formation history prior to the GRB redshift.INTRODUCTION The high redshift frontier of observational cosmology currently stands at redshifts z ≈6.The current redshift record is a quasar at z =5.8,and a few galaxies are known at marginally lower redshift.Beyond z =6,we have yet to identify any individual objects.We do know that hydrogen was predominantly neutral at redshifts z ∼>30based on the observed anisotropy of the cosmic microwave background,which would be smoothed out by Thomson scattering if the free electron density at z ∼>30were too great.The redshift range 6∼<z ∼<30remains unknown territory.It is a very interesting territory,too,for it should include the formation of the first stars,galaxies,and quasars,and certainlyincludes the epoch at which hydrogen was reionized.Searches for starlight (and other rest-frame near ultraviolet tracers)can make incre-mental progress into the low-redshift end of this period.However,these methods face a practical limit where the Lyman break redshifts out of the optical window to the near-infrared,at z ≈7.At higher redshift,essentially no flux is expected in the optical window (observed wavelengths 0.36µm ∼<λobs ∼<1µm ).Atmospheric conditions and present de-tector technologies conspire to make searches at λobs ∼>1µm much less efficient.Future instrumentation like the Next Generation Space Telescope (NGST)promise extensions of “conventional”optical methods to the observed near-IR and thus to redshifts z ≫6,but this may be a decade or more away.In the meantime,we expect the upcoming ex-tension of our Large Area Lyman Alpha (LALA)survey (Rhoads et al 2000;Malhotra et al 2001)to z =6.6to be at or near the practical limit for some years.We would like to find tracers of z >6objects that are accessible now.Fortunately,this is possible so long as we are willing to use something besides starlight.In practice,this means higher energy photons(γand x-rays),since lower energies still face either confusion or sensitivity issues.Gamma ray bursts(GRBs)are an excellent candidate for detection at high redshift because the bursts and their afterglows are extremely bright at all wavelengths.Two conditions must be met for such a candidate to work well.First,there should be a reasonable expectation that the object exists at high redshift;and second,it should be detectable there.The best argument that gamma ray bursts should occur at high redshift comes from the growing body of evidence linking GRBs to star formation activity(and hence presumably to the deaths of massive,short-lived stars):GRB host galaxy colors are characteristically blue(Fruchter et al1999);the spatial distribution of GRBs on their hosts matches expectations for hypernova models(Bloom,Kulkarni,&Djorgovski 2000);and the emission lines of GRB host galaxies are unusually strong(Fruchter et al 2001).Structure formation models yield estimated redshifts z∼15±5for thefirst stars to form in the universe(cf.Barkana&Loeb2001).This is supported by studies of heavy element abundances:It has proven extremely difficult tofind objects with primordial (i.e.,big bang nucleosynthesis)abundances at any redshift currently accessible.The immediate inference is that a substantial generation of stars must have existed at earlier redshifts to produced the ubiquitous metals.The association of GRBs with star formation then implies that thefirst GRBs also occurred in the redshift range z∼15±5.The detectibility of GRBs at z≫6has been considered in detail by Lamb&Reichart (2000),whofind that the bright end of the luminosity distribution would be detectable at very high redshifts(though quantitative predictions depend substantially on unknown details of the GRB luminosity function).This applies also to the X-ray and optical after-glows,for which time dilation of the most distant afterglows helps offset the increase in luminosity distance with redshift(Lamb&Reichart2000;Ciardi&Loeb2000).The Lyman break will render afterglows at z>7invisible to optical detectors,just as it does for galaxies.But the problem here is not so serious.Searches for z>7galaxies suffer because galaxies at such high redshifts are faint,and the required combination of large solid angles and high sensitivity tofind them is not yet practical at near-IR wavelengths.Because GRB afterglows outshine their host galaxies at early times,and because X-ray detectors can determine GRB locations with accuracy comparable to the current near-IRfield of a4m class telescope,an afterglow at this redshift is easier tofind than are the galaxies around it.Indeed,published near-infrared afterglow observations (Rhoads&Fruchter2001)already achieve a sensitivity sufficient to detect afterglows at z∼10for several hours following a GRB(cf.figures2,3of Lamb&Reichart2000). The followup program described in Rhoads&Fruchter2001is continuing at the NASA Infrared Telescope Facility,and we have a similar program at the National Optical Astronomy Observatory.The observed signature of a z>7GRB would be a near-infrared afterglow exhibiting a Lyman break atλobs=0.1215(1+z)µm>1µm.Such breaks have been used to measure z=2.05for GRB000301C(Smette et al2001)and to estimate z≈5for GRB980329(Fruchter1999;see also Reichart et al1999).Their extension to longer wavelengths is straightforward.Thus,it is reasonable to expect that z>7GRBs will be detected with current technology.The prospect of detecting gamma ray bursts at z>7opens two possible methods of studying star formation activity at these epochs:GRB rate evolution,which should tracestar formation activity;and pair production cutoffs in the GeV spectra of bursts,which probe the total optical-ultraviolet background light produced by high redshift stars.BURST RATE EVOLUTIONThe most basic inference from the observed burst rate is that the highest redshift where a burst has been detected z max,grb implies the onset of star formation at some redshift z max,∗>z max,grb.It is likely that in fact z max,∗≈z max,grb:The association of GRBs with star formation tracers requires short progenitor lifetimes(≪108years),so the redshift difference between thefirst stars formed and the earliest possible hypernovae is small. It will be possible to go further by measuring the GRB rate as a function of red-shift,R grb(z),and taking it as a surrogate for the star formation rate.Such studies would require a large sample(several tens)of high redshift GRBs,together with an under-standing of the selection effects that went into the sample.This method is likely to be limited by at least two systematic factors.First,uncertainties in the GRB luminosity function will introduce uncertain corrections to the inferred total GRB rate and the in-ferred star formation rate,since the high redshift sample will contain only bright bursts. Second,evolution in the burst progenitor population may influence the burst rate.One plausible example is that the GRB rate could depend on progenitor metallicity,which is likely to be lower in the early universe.Another is that the stellar initial mass function (IMF)may vary,thereby affecting the relation between GRB rate and star formation rate, and perhaps also the shape of the GRB luminosity function.Possible evidence for IMF variations has recently been found in at some high redshift Lymanαemitting galaxies (Malhotra et al2001).Overall,these complications suggest that calibration of the GRB rate as an indicator of global star formation might be possible to within a factor of a few.While higher accura-cies would be desirable,the present uncertainties with more conventional star formation estimators are not much better.For example,rest ultraviolet continuum measurements are corrected by a factor of∼7for dust absorption,and the uncertainty in this correction could easily be a factor of two given the range of possible dust properties.PAIR PRODUCTION CUTOFFS IN GRB SPECTRAThe observed spectra of gamma ray bursts sometimes extend to very high photon energies:The EGRET experiment on the Compton Gamma Ray Observatory detected four bursts with unbroken power law tails extending to Eγ>1GeV,and the Milagrito air shower experiment has tentatively detected one burst at Eγ∼>1TeV.Photons withsuch high energies have mean free paths shorter than a Hubble distance due toγ+γ→e++e−interactions with low energy background photons.The threshold for such pair production reactions is Eγεγ>m2e c4=(511keV)2,corresponding to the requirement that each photon have the rest mass energy of an electron in their center of momentum frame. (Here Eγandεγare the two photon energies measured in an arbitrary frame,and Eγ≥εγby convention.)The cross section(for a head-on collision)peaks at Eγεγ=2m2e c4andfalls asymptotically as1/(Eγεγ)for Eγεγ≫2m2e c4.Pair production cutoffs in the TeV gamma ray spectra of blazars due to interactions with the cosmic infrared background have been predicted(Stecker,De Jager,&Salamon 1992;MacMinn&Primack1996;Madau&Phinney1996;Malkan&Stecker1998)and observed(e.g.,De Jager,Stecker,&Salamon1994;Konopelko et al1999)for several years now.The extension of the same physics to higher redshifts and lower gamma ray energies has been explored recently by several groups(Salamon&Stecker1998; Primack et al2000;Oh2000).The observer frame gamma ray energy determines simultaneously the redshift and rest frame energies of the background photons that dominate the pair production optical depth.At low redshifts(z≪1),the effective absorption coefficientα(Eγ)increases with Eγand changes relatively little with redshift,so that the relevant physics is simply α(E cut)d=1,with d the distance to the source.However,at z∼>1,redshift effects become important:The threshold energyεγ(z)∝1/(1+z),and the background radiation field will also evolve with redshift.The optical depth for photons near E cut is therefore dominated by absorption at high redshift,unless the source redshift is so high as to precede the creation of any substantial optical-IR background.By the time the photon reaches lower redshifts,the threshold for pair creation grows so large that the density of relevant photons is extremely low.Oh(2000)has shown that the highest energy background photons capable of producing optical depthτ≈1over a Hubble distance have energies below the ionization threshold for hydrogen(i.e.,εγ<13.6eV),since hydrogen absorption in stellar atmospheres,galaxies,and the intergalactic medium ensures a strong decrement in background photon number density at13.6eV.The most robust observable consequence of the pair creation cutoff is the observer frame gamma ray energy E cut(z)for which the optical depthτ=1.Lower pair creation optical depths(τ≪1)cannot be measured reliably because of our imperfect knowledge of the intrinsic(i.e.,unabsorbed)source spectrum,while at higher optical depths(τ≫1) the absorption reduces theflux below detection thresholds of present or near-future instruments.We might measureτ(Eγ)with reasonable accuracy over the range1/2∼<τ∼<2.Detailed predictions of E cut(z)differ from model to model,depending on the the-oretical treatment adopted for the earliest star formation(see Primack et al2000;Oh 2000).For example,the observer frame energy whereτ=1for redshift z=6is 4GeV∼<E cut(6)∼<6GeV for different models in Primack et al(2000),and10GeV∼< E cut(6)∼<26GeV for models in Oh(2000).Therein lies the power of this method for learning about thefirst generations of stars,for these strong differences in predictions allow the models to be distinguished with comparative ease from even a modest data set. Moreover,if we can observe the GeV cutoffs in spectra of a few GRBs spread over the redshift range6∼<z<z max,∗,we can infer the evolution of the optical-UV background radiation over the same period with little dependence on models.This follows because the difference in pair creation optical depth between two bursts at redshifts z1and z2 (z1<z2)is determined only by the background radiation in the range z1<z<z2.DISCUSSIONThe two methods of using gamma ray bursts to probe high redshift star formation com-plement each other in many ways.GRB rate measurements at high redshift are techni-cally easier.They require a GRB monitor plus rapid multiband near-infrared followup. Existing instrumentation and indeed existing observational programs are already ade-quate for this work.Pair creation cutoffs require one additional observation,namely,a GeV energy spectrum obtained during the GRB.This GeV spectrum will have to come from GLAST or a similar space mission.The physical assumption behind the GRB rate evolution method is that the bursts are associated with star formation activity.Under this assumption,there will be some systematic uncertainties in converting the GRB rate to the star formation rate(see above).In contrast,the pair creation cutoff method requires only that some high redshift GRBs have GeV spectra that are sufficiently bright and sufficiently smooth for the cutoff to be observed.Beyond this,there is no requirement on the nature of the bursters,which are needed only as beacons to probe the intervening background radiation.The physics of pair creation is then well understood and probes the total background radiation produced by high redshift stars.Thus,combining the two methods of studying high redshift star formation with GRBs may overcome the physical uncertainties of either method alone.Additional constraints from other techniques using other classes of objects(galaxies observed at infrared wavelengths,or quasars at X-ray wavelengths)will become available over the next few years,and will again have complementary strengths and weaknesses.By adding these to the GRB results,we can reasonably expect to understand star formation at z∼10as well as we understand it at z∼3today.REFERENCES1.Barkana,R.,&Loeb,A.2001,Physics Reports,in press2.Bloom,J.S.,Kulkarni,S.R.,&Djorgovski,S.G.2000,submitted to AJ,astro-ph/00101763.Ciardi,B.,&Loeb,A.2000,ApJ540,6874.De Jager,O.C.,Stecker,F.W.,&Salamon,M.H.1994,Nature369,2945.Fruchter,A.S.,et al1999,ApJ519,L136.Fruchter,A.S.1999,ApJ512,L17.Fruchter,A.S.,et al20018.Konopelko,A.K.,Kirk,J.G.,Stecker,F.W.,&Mastichiadis,A.1999,ApJ518,L13mb,D.Q.,&Reichart,D.E.2000,ApJ536,110.MacMinn,D.,&Primack,J.R.1996,Space Science Reviews75,41311.Madau,P.,&Phinney,E.S.1996,ApJ456,12412.Malhotra,S.,et al2001,in preparation13.Malkan,M.A.,&Stecker,F.W.1998,ApJ496,1314.Oh,S.P.2001,to appear in ApJ,astro-ph/000526315.Primack,J.R.,Somerville,R.S.,Bullock,J.S.,&Devriendt,J.E.G.2000,astro-ph/001147516.Reichart,D.E.,et al1999,ApJ517,69217.Rhoads,J.E.,Malhotra,S.,Dey,A.,Stern,D.,Spinrad,H.,&Jannuzi,B.T.2000,ApJ545,L8518.Rhoads,J.E.,&Fruchter,A.S.2001,ApJ546,11719.Salamon,M.H.,&Stecker,F.W.1998,ApJ493,54720.Stecker,F.W.,De Jager,O.C.,&Salamon,M.H.1992,ApJ390,L49。

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。

㊀2024年第1期No.1㊀2024四川大学学报(哲学社会科学版)Journal of Sichuan University (Philosophy and Social Science Edition )总第250期Sum No.250ɦ历史学研究ɦ马修·帕里斯的行程地图与中世纪地图制作者世界观的转变陈志坚摘㊀要:13世纪中后期,英格兰本笃修士马修㊃帕里斯及其后继者在圣奥尔本斯修道院创作了一系列行程地图㊂这些地图原是编年史抄本序章中的一部分,不仅包括自伦敦至南意大利阿普利亚的分段路线图,还包含作为此行程出发地与目的地 不列颠与巴勒斯坦的区域地图㊂长期以来,研究者多以传统的宗教进路来解读这些行程地图,视其为一种精神的朝圣之旅,认为作者旨在为那些不能亲临圣地的修士开启一次通往天上耶路撒冷的富有想象力的旅程㊂然而,以抄本古文字学与古抄本学方法考察这些行程地图可发现,它们不仅在外观上呈现出与传统基督教地图迥然不同的特征,还在很大程度上呼应了金雀花王朝统治者扩张领土以建立帝国的野心与欲求㊂不仅如此,基于新近复兴的古典地理学知识,这些行程地图的实用性㊁精确性与科学性也在一定程度上得到增强㊂关键词:马修㊃帕里斯;世界之布;行程地图;中世纪;世界观中图分类号:K561.32㊀㊀文献标志码:A㊀㊀文章编号:1006-0766(2024)01-0129-14作者简介:陈志坚,首都师范大学历史学院教授(北京㊀100089)①㊀Simon Lloyd and Rebecca Reader, Paris,Matthew (c.1200-1259),Historian,Benedictine Monk,and Polymath, in H.C.G.Matthew and Brian Harrison,eds.,Oxford Dictionary of National Biography :From the Earliest Times to the Year 2000,vol.42,Oxford:Oxford University Press,2004,p.622.②㊀Richard Vaughan, The Handwriting of Matthew Pairs, Transactions of the Cambridge Bibliographical Society ,vol.1,no.5(1953),p.389;Richard Vaughan,Matthew Paris ,Cambridge:Cambridge University Press,1958,pp.236-243;Suzanne Lewis,The Art of Matthew Paris in the Chronica Majora ,Berkeley:University of California Press,1987,pp.321-323;Evelyn Edson,Mapping Time and Space :How Medieval Mapmakers Viewed Their World ,London:The BritishLibrary,1997,pp.118-120.13世纪的英格兰本笃修士马修㊃帕里斯(Matthew Paris)是一位历史学家,其本职工作是为其所属的圣奥尔本斯修道院(St Albans Abbey)创作一部编年史,即为后人所熟知的‘大编年史“(Chronica Maiora )㊂除此之外,马修还是一名地图制作者,他先后绘制了4种包含伦敦至阿普利亚(Apulia)的路线图(以下简称 路线图 )以及巴勒斯坦区域地图㊁不列颠区域地图在内的行程地图(以下简称 行程地图 )㊂马修的这些地图 具有重要意义,这并不是因为它们所具有的时代影响力,而是因为它们的独创性,马修正在尝试他那个时代不为人知的制图理念,而且这些制图理念在当时还没有被普遍理解 ㊂①在马修生活的年代,体现基督教宗教理念的T -O 地图居于主导地位,势头正盛㊂与之相比,马修的地图在基本方向㊁实用性与精确性方面呈现出极大的创新性㊂从某种意义上来说,马修是一名早熟的制图者,其地图所呈现的先进制图理念一直处于领先地位,直到中世纪末期波特兰海图(portolan chart)的诞生㊂自吉尔森于1928年将马修绘制的4种不列颠地图制版刊行以来,学者对于这些不列颠地图以及与之密切相关的行程地图给予了广泛关注㊂研究者首先对于行程地图的创作者及创作时间进行初步探讨并普遍认可抄本古文字学家理查德㊃沃恩通过分析马修的字体得出的结论,即认为 这些行程地图均是圣奥尔本斯修道院修士马修及其后继者创作的 ㊂②马修不仅是一位出色的编年史家,还是一921四川大学学报(哲学社会科学版)总第250期位杰出的抄本缩微图画家,他在绘制抄本缩微图㊁地图㊁人物画像时擅长用稀释颜料对深色墨水勾勒的草图进行着色以制造一种水洗的效果,从而开创了一种 着色绘画 (tinted drawings)的风格㊂正因如此,在后来的艺术史中,这一类型的彩色绘画往往被称为 圣奥尔本斯流派 (School of St Albans)或 马修㊃帕里斯流派 (School of Matthew Paris)㊂有学者以绘画风格为标准对行程地图进行研究,也印证了沃恩的上述结论㊂①另外,行程地图的来源也从一个侧面佐证了上述观点 它们大都来自马修及其后继者所编纂的编年史抄本之中,部分来自圣奥尔本斯修道院官方文献汇编或者马修最好的合作伙伴兼衣钵继承人沃灵福德的约翰(John of Wallingford)的札记簿㊂②然而,在上述一致的观点之外,学者在很多问题上仍存疑问㊂例如,行程地图中包含的小单元,如路线图㊁不列颠区域地图㊁巴勒斯坦区域地图,是独立的存在,抑或是一个有机的整体?马修及其后继者绘制这些行程地图的意义何在?它们又反映了制图者的何种观念?早期研究者倾向于否认路线图㊁巴勒斯坦区域地图与不列颠地图之间的联系,认为它们只是因为抄本装帧而被偶然并置,彼此之间并无必然联系㊂例如,沃恩以及更早的研究者比兹利就持这种观点㊂③不仅如此,早期研究者还倾向于认为,行程地图与编年史插图具有同样的功能,是作者为了阐释㊁说明编年史文本而制作,目的是将编年史中提到的城市㊁城镇㊁河流㊁山脉等等风物具象化㊁空间化,从而帮助阅读者更好地理解编年史㊂持这一观点的主要有苏珊娜㊃刘易斯与伊芙琳㊃埃德森㊂④进入21世纪以来,研究者有了两类新发现㊂其一,学者逐渐认识到,路线图与区域地图并非编年史的附属物,编年史中所提及的很多地名如耶路撒冷㊁阿卡与开罗等,与地图上的地名并无一一对应关系㊂换言之,绘制地图并非为了向读者展示上述地名所在的位置,在很大程度上,路线图㊁区域地图与编年史是一种平行关系㊂⑤其二,学者通过进一步研究发现了路线图与区域地图之间的联系㊂例如,在阿普利亚地图的左上角,马修标记了如下文字: 此为通过阿普利亚去往阿克的路线㊂ 再如,在不列颠地图中也隐藏着伦敦与多佛之间的路线图,这在很大程度上可被视为路线图中的英格兰部分㊂再如,在西西里岛的最末端一个叫特拉帕尼(Trapes)的地方,马修标注道: 理查德伯爵从圣地返回时曾经过这里㊂ ⑥这些发现让绝大多数学者相信,路线图与区域地图之间存在联系,并构成一个有机的整体㊂以此为基础,学者开始构建这些路线图与区域地图的整体性意义㊂丹尼尔㊃康诺利提出了 想象的朝圣 的概念,认为路线图㊁巴勒斯坦地图与不列颠地图构成了一套完整的行程地图,从而为那些不能离开圣奥尔本斯修道院远行的修士打造了一次精神的朝圣之旅㊂康诺利还指出,这种行程地图与修道院回廊中所绘制的朝圣图有异曲同工之妙,但前者效果更佳,因为修士在阅读中自然会用手去翻动书叶,然后目光跟着路线图上下移动,口中默念着地图中的说明文字㊂到达阿普利亚所在叶面时,修士还可通过操作可折叠的侧翼,想象着后续的海上路线㊂如此一来,修士的手㊁眼㊁心㊁口等身体部位将会深度参与这一想象的朝圣之旅,从而在更大程度上营造出身临其境的031①②③④⑤⑥M.R.James, The Drawings of Matthew Paris, The Walpole Society ,vol.14(1925-1926),pp.1-26.有证据表明,沃灵福德的约翰曾对一幅从马修那里获得的不列颠地图增补了系列内容,参见Vaughan,Matthew Paris ,p.243;也有学者指出,Royal 抄本中的不列颠地图D 很有可能是马修的后继者为了呼应爱德华一世对苏格兰的领土主张而制作,参见Daniel K.Connolly, Copying Maps by Matthew Paris:Itinerary Fit for A King, in Palmira Brummett,ed.,The Book of Travels :Genre ,Ethnology ,and Pilgrimage ,1250-1700,Leiden:Brill,2009,pp.196-199.Vaughan,Matthew Paris ,p.247;C.R.Beazley,The Dawn of Modern Geography :A History of Exploration and Geographical Science from the Close of the Ninth to the Middle of the Thirteenth Century c .900-1260,vol.2,London:Henry Frowde,Amen Corner,1901,p.588.Lewis,The Art of Matthew Paris in the Chronica Majora ,pp.324-325;Edson,Mapping Time and Space ,pp.123-124.P.D.A.Harvey,Medieval Maps of the Holy Land ,London:The British Library,2012,pp.74-75.Katharine Breen, Returning Home from Jerusalem:Matthew Paris ̓s First Map of Britain in Its Manuscript Context, Representations ,vol.89,no.1(Winter 2005),pp.73,77.陈志坚:马修㊃帕里斯的行程地图与中世纪地图制作者世界观的转变2024年第1期氛围㊂①凯瑟琳㊃布林则更进一步,将往往被置于最后的不列颠区域地图理解为朝圣行程的返程部分,从而构建了一个更加完整的朝圣行程㊂②尽管在中世纪基督教制图观念占主导地位的大背景下,以精神朝圣的思路理解行程地图颇有阐释力,但仍无法完整地解释其中的一些元素,特别是相对于主流的基督教制图观念而言颇具创新性的部分,诸如:路线图以南为上,不列颠地图以北为上的朝向;路线图中精确标注里程的条状直线;对南意大利的关注程度远远胜过罗马;在巴勒斯坦地图中,对阿克城墙㊁城堡等军事防御设施描述的详细程度远远胜过耶路撒冷;4种不列颠区域地图自身存在的差异及流变等㊂近年来,有学者已意识到这些问题,并开始尝试在宗教观念之外的政治㊁历史语境中解读行程地图㊂如维多利亚㊃莫尔斯注意到地图的政治用途在13世纪的英国得到长足发展,并认为马修的路线图与区域地图在一定程度上展示了地图作为统治和知识象征的力量,或许正是在此意义上,西西里和阿克分别在南意大利与巴勒斯坦区域地图中被重点强调㊂③丹尼尔㊃伯克霍尔茨追溯了亨利三世与爱德华一世对地图的兴趣,并认为他们很有可能利用地图体现其对领土与权力的野心㊂④康诺利的最新研究表明,Royal 抄本中的不列颠地图D 实际上呼应了爱德华一世对苏格兰领土的主张㊂⑤由此可见,近年来学者的研究虽然开启了一个全新的研究路径,但相关研究成果或失之于简,仅是一个初步的判断;或无意做整体性探讨,仅涉及问题的一个方面㊂笔者拟以抄本古文字学(paleography)与古抄本学(codicology)方法考察马修绘制的行程地图,以期在梳理传统基督教制图观念的基础上揭示其全新的制图理念,并尝试评估金雀花王朝的政治诉求于此过程中所扮演的角色㊂一㊁马修㊃帕里斯其人及其行程地图马修㊃帕里斯,亦称巴黎人马修(Matthew the Parisian),出生于1200年左右,并于1217年进入圣奥尔本斯修道院成为一名本笃会修士㊂圣奥尔本斯修道院于公元793年由麦西亚国王奥法(Offa)捐资修建,到马修生活的年代,也已存在400余年㊂该修道院不仅具有悠久的历史,更以其撰史传统而闻名,这在很大程度上得益于其与王室的密切关系㊂1236年,马修继承了该修道院编年史家温多弗的罗杰(Roger of Wendover)的衣钵,就此开始了其撰史生涯㊂在马修领衔撰史期间,修道院与王室的关系变得更为密切㊂不仅国王亨利三世经常到访修道院,马修也经常被邀请参加宫廷重要活动㊂据记载,亨利三世曾于1244至1257年间先后8次到访修道院,每次都捐赠大量布帛㊁财物㊂1251年,亨利三世到访时送给修道院3块丝绸布料,并且还特意询问马修他已向修道院捐赠了多少块丝绸布料,以及修道院是否已遵照他的命令,在这些丝绸布料上都写上 英王亨利三世捐 字样㊂国王得到的答案是31块,而且没有其他国王捐过如此之多㊂不仅如此,马修还与亨利三世保持着良好的个人关系,常常出入宫廷,有资格与国王共桌就餐㊁亲密交谈,甚至可以当面向国王抱怨其遭遇的不公㊂另外,国王还是马修的赞助人,曾亲自委托他撰写‘忏悔者爱德华生平“一书㊂1247年,在威斯敏斯特大厅举行的一场盛大仪式上,亨利三世发现了马修,特地让他坐在自己身边,并要求他记录当日发生之事㊂随后,国王还邀请马修共进晚餐㊂1257年,马修在国王的宫廷里逗留了一周,在此131①②③④⑤Daniel K.Connolly, Imagined Pilgrimage in the Itinerary Maps of Matthew Paris, The Art Bulletin ,vol.81,no.4(1999),pp.598-599;Daniel K.Connolly,The Maps of Matthew Paris :Medieval Journeys through Space ,Time and Liturgy ,Woodbridge:The Boydell Press,2009,pp.1-2.Breen, Returning Home from Jerusalem, pp.63,87.Victoria Morse, The Role of Maps in Later Medieval Society:Twelfth to Fourteenth Century, in David Woodward,ed.,The History of Cartography ,vol .3,Cartography in the European Renaissance ,Part 1,Chicago:The University of Chicago Press,2007,pp.35,39,41-42.Daniel Birkholz,The King ̓s Two Maps :Cartography and Culture in Thirteenth-Century England ,New York &London:Routledge,2004,pp.12-13.Connolly, Copying Maps by Matthew Paris, pp.196-199.四川大学学报(哲学社会科学版)总第250期期间与国王形影不离,无论国王 在餐桌边,在宫殿里,还是在房间里 ,由此,他从国王那里获得了大量信息㊂①遵循着圣奥尔本斯修道院的撰史传统,并基于不断从宫廷中获得的第一手资料,马修写出了大量历史著作㊂在马修撰写的史著中,‘大编年史“与‘英吉利人史“(Historia Anglorum )最负盛名㊂从著述体例上讲,前者属于普遍史,涵盖自创世至1259年的世界历史,是马修在温多弗的罗杰所著编年史‘历史之花“(Flores Historiarum )的基础之上编纂而成的㊂后者则属于专门史,侧重讲述英吉利人的历史,其绝大部分史料来源于‘大编年史“,实际上是‘大编年史“中与英吉利人相关史料的汇编本㊂除此之外,马修后来还在‘英吉利人史“的基础上推出一个更加简略的版本,名为‘英吉利人史简编“(Abbreuiatio Compendiosa Chronicorum Anglie )㊂本文所涉及的行程地图便主要来自这几部著作的序章部分㊂但不幸的是,这些著作均未能以其原始的形制完整地流传下来,而是在不断被拆分㊁重组㊁装帧的过程中形成了新的抄本,并由不同的图书馆收藏㊂同样地,行程地图在此过程中亦难免被拆分㊁重组的命运,并最终以零散的状态分处于几个新抄本中㊂马修的‘大编年史“是一部三卷本史书,现分处于三个不同的抄本中㊂其第一卷涵盖自创世至1188年的历史,可见于剑桥大学基督圣体学院所藏引证号为Cambridge,Corpus Christi College,MS 026的抄本之中(以下简称MS 026抄本)㊂该抄本的序章部分涵盖一套相对完整的行程地图(以下简称行程地图1),包括自伦敦至南意大利阿普利亚的路线图以及巴勒斯坦区域地图,但缺少不列颠区域地图㊂②其第二卷涵盖自1189至1253年的历史,可见于剑桥大学基督圣体学院所藏引证号为Cambridge,Corpus Christi College,MS 016的抄本之中(以下简称MS 016抄本)㊂该抄本中的行程地图(以下简称行程地图2)包含不完整的自伦敦至南意大利阿普利亚的路线图㊁巴勒斯坦区域地图以及一幅不列颠区域地图(以下简称地图B)㊂③其中,路线图仅残留自蓬特雷莫利(Pontremoli)至南意大利阿普利亚的部分㊂不仅如此,所有这些地图在MS 016抄本中均以半叶的形式存在㊂④其第三卷涵盖1254至1259年的历史,可见于大英图书馆所藏引证号为Royal MS 14C.VII 的抄本中(以下简称Royal 抄本)㊂该抄本序章部分包含一套完整的行程地图(以下简称行程地图3),包括伦敦至南意大利阿普利亚的路线图㊁巴勒斯坦区域地图以及不列颠区域地图(以下简称地图D)㊂除了‘大编年史“第三卷,Royal 抄本中还包含马修的‘英吉利人史“㊂⑤二者在很大程度上共享抄本前面的序章部分㊂除此之外,在一部名为‘增补册“(Liber Additamentorum )的圣奥尔本斯修道院自用文献中,还存有一套不完整的行程地图(以下简称行程地图4),它仅包含自伦敦至那不勒斯的路线图,可见于大英图书馆藏引证号为Cotton MS Nero D.I 的抄本(以下简称Nero 抄本)㊂⑥行程地图4虽然在风格上与行程地图1㊁2㊁3类似,但在形式和内容方面均相对简略,没有采用常规的一叶两栏形制,而是一叶三栏且忽略所有支线行程,仅绘制主线行程,很有可能是马修在正式绘制行程地图1㊁2㊁3之前的构思草图,后来作为备用资料被收录进修道院自用文献‘增补册“中,与修道院创始人‘奥法生平“(Vitae duorum Offarum )㊁‘历任修道院长生平“(Gesta Abbatum )等文献并列㊂不仅如此,马231①②③④⑤⑥David Carpenter,Henry III :The Rise to Power and Personal Rule ,1207-1258,New Haven and London:Yale University Press,2020,pp.171,454,521,541,551,615,715,521,399,403.Cambridge,Corpus Christi College,MS 026,fols.ir -ivv.1928年,吉尔森(J.P.Gilson)汇集了马修绘制的与其行程地图相关的4张不列颠地图,并将其制成彩色图版出版㊂在该书中,吉尔森将4张地图简称为:地图A㊁地图B㊁地图C㊁地图D,笔者在本文中沿用这一约定俗成的简称㊂参见J.P.Gilson,ed.,Four Maps of Great Britain Designed by Matthew Paris about A.D.1250,Produced from Three Manuscripts in the British Museum and One at Corpus Christi College ,Cambridge ,London:Printed by Order of the Trustees,Sold at the British Museum and by Bernard Quaritch,Ltd,1928,p.3.2003年,基督圣体学院图书馆又对MS 016号抄本进行了重新装帧㊂此时,该抄本又被分为上下两册,抄本前面的序章部分单独装订成册,并被命名为MS 016I,后面的正文部分单独成册,并被命名为MS 016II㊂正文中所述行程地图㊁巴勒斯坦区域地图及不列颠地图部分,参见Cambridge,Corpus Christi College,MS 016I,fols.iiir -ivv.Royal MS 14C.VII,fols.157r -231r,2r -5v,8v -156v,British Library,London.Cotton MS Nero D.I,fols.183v -184r,British Library,London.陈志坚:马修㊃帕里斯的行程地图与中世纪地图制作者世界观的转变2024年第1期修绘制的另外两种不列颠地图明显也与行程地图密切相关,但由于种种原因已被单独装订在其他抄本中:其一,在马修以其‘英吉利人史“为基础缩编而成的‘英吉利人史简编“的序章部分,存在一幅马修绘制的不列颠地图(以下简称地图A),可见于大英图书馆所藏引证号为Cotton MS Claudius D.VI 的抄本中(以下简称Claudius 抄本)㊂①该地图与布鲁图斯(Brutus)至亨利三世的系列国王画像,以及自阿尔弗雷德大帝至亨利三世国王世系图等重要文件并列,共同构成抄本的序章部分;其二,在马修后继者沃灵福德的约翰曾拥有的一本札记簿中,亦存在一幅不列颠地图(以下简称地图C),可见于大英图书馆所藏引证号为Cotton MS Julius D.VII 的抄本中(以下简称Julius 抄本)㊂②该地图明显是由马修绘制,但从其所用色彩及内容看,仍属于较为初级的草图㊂沃灵福德的约翰肯定是从某种途径获得了这张地图并对其进行了一系列改造,包括继续在地图上标注地名,以及在地图背面空白处书写文字㊂最后,他还将该地图两次折叠后与其札记簿装帧在一起㊂该札记簿的核心内容是沃灵福德的约翰摘抄的系列编年史史料,主要摘自马修的‘大编年史“,在一定程度上反映了他向马修学习撰写编年史的实践㊂③二㊁世界之布:中世纪基督教主流制图观念中世纪的地图一般被称作 Mappamundi ㊂其中, mappa 一词在中世纪拉丁语中意为 桌布 或 餐巾 ,可意译为 地图 ;④而 mundi 则是 mundus 一词的拉丁文属格单数形式,意思是 世界的 (of the world)㊂如此一来,具有 世界地图 之意的 Mappamundi 一词其实可直译为 世界之布 ㊂这个词语在古典时代晚期的拉丁语中从来没有被使用过,彼时用来描述地图的词汇一般是 forma (图形)㊁ figura (图像)㊁ orbispictus (区域图)或者 orbisterrarumdescriptio (区域地理描述)㊂尽管在中世纪,世界之布的称谓是最常见的,但在谈及地图时,人们亦有一些其他的表达形式,如 inmaginesmundi (世界的图像)㊁ pictura (图像)㊁ descriptio (描述)㊁ tabula (图表),甚或赫里福德地图中使用的 estoire (历史)㊂⑤但在上述词汇中, 世界之布 词义最为稳定,自8世纪至中世纪末期一直被用来指代以基督教观念描绘世界的图像或文字㊂迄今为止,计有1100余幅这样的地图幸存了下来,其中大部分可见于中世纪的抄本之中,也有独立存在且尺寸相当大的地图,很可能是作为教堂或修道院的挂图使用,例如外形类似房屋山墙的赫里福德地图(Hereford Map),其最长㊁最宽处分别是1.59米和1.34米,是现存最大的 世界之布 ㊂⑥虽名为地图,但 世界之布 并不像今天的地图一样客观地反映空间的比例与尺寸,亦不能为人们出行提供精确的信息,而是一种集合了时间㊁空间㊁事件㊁概念㊁色彩㊁文本㊁意象等元素的复杂集合体,集中反映了基督教有关 神学㊁宇宙学㊁哲学㊁政治学㊁历史学㊁动物学㊁人种学 等知识的理念,是基督教徒眼中的世界形象㊂⑦一般而言,这些地图具有以下特点:它们不仅比例严重失调,以东为上,还呈现出T -O 的特殊形态;整个版面不仅充斥着自创世之日至末日审判的所有重要的圣经事件,还杂以各式各样的奇幻动物和恐怖种族;作为圣地的耶路撒冷一般被安放在地图中心位置,而末日审判的意象则往往被置于地图顶端,这表明 顶部 (新耶路撒冷)而非 中心 (地331①②③④⑤⑥⑦Cotton MS Claudius D.VI,f.12v,British Library,London.Cotton MS Julius D.VII,fols.50v -53r,British Library,London.Vaughan,Matthew Paris ,p.243.Jerry Brotton,A History of the World in Twelve Maps ,New York:Viking Penguin,2013,pp.94-95.David Woodward, Medieval Mappaemundi, in J.B.Harley and David Woodward,eds.,The History of Cartography ,vol .1:Cartography in Prehistoric ,Ancient ,and Medieval Europe and the Mediterranean ,Chicago:University of Chicago Press,1987,p.287.The Hereford Mappa Mundi Trustee Company Ltd,Hereford.Brotton,A History of the World in Twelve Maps ,p.95.四川大学学报(哲学社会科学版)总第250期上耶路撒冷)才是中世纪朝圣者最终的目的地,也是手持 世界之布 的信徒目光最终驻留的地方;①世界之布不仅是空间的展开,还涉及时间,在地图上自东向西(自上而下)包含着一个从创世到救赎的完整叙事;世界之布虽以基督教神学世界观为核心,但也包含一定程度的古典知识,这是早期教父与古典天文㊁自然㊁地理知识成就达成妥协的结果㊂由此,在以下部分笔者将以T -O 形态㊁以东为上㊁中心与朝圣㊁象征主义意象㊁ 历史 叙事㊁奇幻动物与恐怖种族为重点,以赫里福德地图㊁埃布斯托地图(The Ebstorf Map)㊁②诗篇地图(The Psalter Map)㊁③梭利地图(The Sawley Map)④等中世纪地图为主要案例,撮述 世界之布 的典型特征㊂其一,T -O 形态㊂T -O 形态地图是中世纪最为经典的地图样式,其整体外观呈圆形,看起来像一个巨大的字母O,由此标识出地图的边界,其外围环绕着海洋㊂圆形内部的三大水系整体上呈现为一个巨大的大写字母T 形态,从而将圆形大陆分成三大块㊂T 字母横笔画左侧㊁右侧及竖笔画部分分别代表顿河㊁尼罗河和地中海㊂⑤在由字母O 与T 建构的空间之中,上方的半圆是亚洲,下方位于T 字母竖笔画左右两边的区域则是欧洲和非洲,这三大洲又分别代表诺亚(Noah)的三个儿子闪(Shem)㊁雅弗(Japheth)㊁含(Ham)及其后代最初定居的区域㊂⑥实际上,T -O 地图本身亦是古典文化与中世纪基督教观念相互妥协的产物㊂在古典晚期向中世纪过渡的关键期,部分早期教父如德尔图良(Tertullian)㊁圣西普里安(St Cyprian)和圣安布罗斯(St Ambrose)等都极端敌视古代的学术成就,而与此同时也有一部分早期教父如奥古斯丁(St Augustine)㊁圣哲罗姆(St Jerome)以及圣伊西多尔(Isidore of Seville)等则主张吸收与借鉴古典学术成就㊂例如奥古斯丁就认为, 如果缺乏对天㊁地㊁世界等要素的相关知识,我们就无法更好地理解圣经 ,他还声称, 为了更好地理解神的造物,在研习圣经的时间和历史时,也须了解空间与地理 ㊂圣哲罗姆遵从奥古斯丁的建议,在翻译圣经之余还撰写了一部名为‘地点之书“(Liber locorum )的著作,并在书中给出了巴勒斯坦和亚洲的区域地图㊂⑦圣伊西多尔则在借鉴古典历史学家萨卢斯特(Sallustius)关于三大洲的相关记载的基础上,首次提出了T -O 地图的构想,其著作‘论事物的本质“(De natura rerum )与‘关于词源学的二十卷书“(Etymologiarum sive originum libri XX )被认为是最早包含T -O 地图意象的作品㊂⑧因早期的T -O 地图在本质上只是一种简要的示意图,仅标注三大洲名称或诺亚三个儿子的名字,很少有其他地名,所以其在T -O 地图的整体分类法中也常常被称作是概要性三部分T -O 地图(Schematic Tripartite)㊂8至11世纪,T -O 地图继续吸收来自马克罗比乌斯(Macrobius)和奥罗修斯(Orosius)等古典学者作品中的知识,发展出了非概要性三部分T -O 地图(Nonschematic Tripartite)㊂这一新子类虽仍将有人居住的大陆分成三部分,但并不严格按照T -O 模式绘制,而是按照各部分的历史及其起源进一步细化与划分各自的区域㊂它们通常强调地中海,并倾向于将海岸线绘制成参差不齐的效果㊂⑨总之,T -O 地图是古典知识与中世纪基督教世界观不断融合的结果,早期教父吸收了古典时代学者将有人居住的世界分成三部分的描述,并将其与创世纪中的世界起源观念结合起来,奠定了中世431①②③④⑤⑥⑦⑧⑨包慧怡:‘感官地图上的灵魂朝圣之旅 中古英语长诗 珍珠⓪的空间结构“,‘外国文学评论“2007年第2期㊂Kloster Ebstorf,Ebstorf,Germandy (destroyed in 1943,20th replica).Additional MS 28681,f.9r,British Library,London.有时亦称 美茵茨的亨利地图 (Henry of Map),参见Cambridge,Corpus Chisti College,MS 66,p.2.Catherine Delano-Smith, The Intelligent Pilgrim:Maps and Medieval Pilgrimage to the Holy Land, in Rosamund Allen,ed.,Eastward Bound :Travel and Travellers ,1050-1550,Manchester:Manchester University Press,2004,pp.110-111;Brotton,A History of the World in Twelve Maps ,p.105.Saint Bede,On Genesis ,trans.Calvin B.Kendall,Liverpool:Liverpool University Press,2008,p.24;Naomi Reed Kline,Maps of Medieval Thought :The Hereford Paradigm ,Woodbridge:Boydell Press,2003,p.13.Brotton,A History of the World in Twelve Maps ,pp.102-103.Burgerbibliothek,cod.417,f.88v,Bern;Kline,Maps of Medieval Thought ,p.13.Woodward, Medieval Mappaemundi, in Harley and Woodward,eds.,The History of Cartography ,vol .1,pp.343,347.。