A revised catalogue of EGRET gamma-ray sources
aa r X i v : . [ a s t r o - ph ] J un Astronomy&Astrophysicsmanuscript no. Casandjian˙Grenier˙08 c (cid:13)
ESO 2018October 29, 2018
A revised catalogue of EGRET γ -ray sources Jean-Marc Casandjian and Isabelle A. Grenier Laboratoire AIM, CEA / DSM - CNRS - Universit´e Paris Diderot,Service d’Astrophysique, CEA Saclay, 91191 Gif sur Yvette, Francee-mail: [email protected] & [email protected]
Received ; accepted
ABSTRACT
Aims.
We present a catalog of point γ -ray sources detected by the EGRET detector aboard the Compton Gamma Ray Observatory.We have used the whole γ -ray dataset of reprocessed photons at energies above 100 MeV together with new Galactic interstellaremission models based on recent CO , HI , dark gas, and interstellar radiation field data. Two di ff erent assumptions have been used forthe cosmic-ray distribution in the Galaxy to explore the resulting systematic uncertainties in source detection and characterization. Methods.
We have used the same 2-dimensional maximum-likelihood detection method as for the 3rd EGRET catalogue.
Results.
The revised catalogue lists 188 sources, 14 of which are marked as confused, compared to the 271 entries of the 3rd EGRET(3EG) catalogue. 107 former sources have not been confirmed because of the additional structure in the interstellar background. Thevast majority of them were unidentified and marked as possibly extended or confused in the 3EG catalogue. In particular, we do notconfirm most of the 3EG sources associated with the local clouds of the Gould Belt. Alternatively, we find 30 new sources with no3EG counterpart. The new error circles for the confirmed 3EG sources largely overlap the previous ones, but several counterparts ofparticular interest that had been discussed in the litterature, such as Sgr A*, radiogalaxies and several microquasars are now foundoutside the error circles. We have cross-correlated the source positions with a large number of radio pulsars, pulsar wind nebulae,supernova remnants, OB associations, blazars and flat radiosources and we find a surprising large number of sources (87) at alllatitudes with no counterpart among the potential γ -ray emitters. Key words.
Egret, gamma-ray source, catalog
1. Introduction
The Energetic Gamma-Ray Experiment Telescope (EGRET),which operated on board the Compton-Gamma Ray Observatoryfrom April 1991 to May 2000, detected photons in the 20 MeVto 30 GeV range. The observation program made use of thelarge instrumental field of view (25 ◦ in radius) to cover thewhole sky and for in-depth studies of specific regions. The re-sulting exposure and flux sensitivity to point sources are there-fore not uniform across the sky. The sensitivity threshold alsovaries because of the intense background emission that arisesfrom cosmic-ray interactions with the interstellar gas and pho-ton fields in the Milky Way. The minimum flux that EGRETcould detect steeply rises with decreasing Galactic latitude. Inorder to detect point sources and assess their significance inthese varying conditions, a 2-dimensional maximum-likelihoodmethod using binned maps had been developed for the COS-B data (Pollock et al., 1981) and implemented for the EGRETone (Mattox et al., 1996). A first catalog using this method waspublished after 1.5 years of data (Fichtel et al., 1994), followedby the second one (Thompson et al., 1995) and its supplement(Thompson et al., 1996) after 3 years of data. Lamb & Macomb(1997) presented a catalog of sources detected above 1 GeV.The last EGRET catalog (hereafter 3EG, Hartman et al., 1999)comprised reprocessed data from April 1991 to October 1995with the interstellar emission model from Hunter et al. (1997)and extragalactic background from Sreekumar et al. (1998).This version contained 271 point sources including a solar flare,the Large Magellanic Cloud, five pulsars, one radiogalaxy de- Send o ff print requests to : J.-M. Casandjian tection (Cen A), 66 high-confidence identifications of blazars(BL Lac objects and flat-spectrum radio quasars), and 27 lower-confidence blazar identifications. Because of the wide tails ofthe instrument point-spread function, seven potential artifactswere noted around the brightest sources and many sources weremarked as confused or possibly extended.The 3EG catalogue also contained 170 sources with no at-tractive counterpart at lower energy. About 130 of them re-main unidentified as of today (see Grenier (2004) and refer-ences therein). Candidate counterparts that have been searchedfor include pulsars and their wind nebulae, supernova rem-nants, massive stars, X-ray binaries and microquasars, blazarsand nearby radiogalaxies, luminous infrared and starburst galax-ies, and galaxy clusters. It was also noticed (Grenier, 1995,Grenier, 2000, Gehrels et al., 2000) that the most stable uniden-tified sources are significantly correlated with the nearby GouldBelt, a system of massive stars and interstellar clouds that sur-rounds the Sun at a distance of hundreds of parsecs. The o ff setposition of the Sun with respect to the Belt centre and the Beltinclination of 17 ◦ to the Galactic plane indeed provides a usefulspatial signature across the sky (Perrot & Grenier, 2003).EGRET went on observing for another 4.5 years afterthe 4 cycles used for the 3EG work. Its sensitivity was re-duced because of the ageing gas in the spark chamber, butit gathered nearly ten percent more photons and saw sev-eral new variable sources. Several authors (Nolan et al., 2003,Sowards-Emmerd et al., 2005), however, noticed discrepanciesbetween their studies and at least five 3EG sources. Theyfailed to confirm sources and found others. The whole γ -ray dataset and final instrument response functions have Jean-Marc Casandjian and Isabelle A. Grenier: A revised catalogue of EGRET γ -ray sources also been significantly reprocessed by the EGRET team in2001. Furthermore, the spatial coverage of the CO surveyshas reached higher latitudes since 1999, finding new small CO clouds (Dame et al., 2001). In parallel, new HI surveys(Kalberla et al., 2005) have been completed to correct for thesignificant contamination of stray radiation in the older ones.Finally, an additional ’dark’ gas component has been found inthe Gould Belt clouds that significantly increases their mass andspatial extent (Grenier et al., 2005). The additional mass is struc-tured into large envelopes around the dense CO cores. They donot follow the HI and CO maps commonly used to trace atomicand molecular column-densities. So, the dark gas provides both γ -ray intensity and structure that were not accounted for in the3EG background model.For all these reasons and in preparation of the new GLASTmission, it was necessary to revise the interstellar backgroundmodel and to apply the EGRET detection method to the full nineyears of data to build a new catalogue of sources above 100 MeV.In order to study the systematic uncertainties induced on sourcelocations and fluxes by our limited knowledge of the intense in-terstellar background, we have applied the analysis to two dif-ferent background models exploiting the same new interstellardata, but using di ff erent approaches to constrain the cosmic-raygradient across the Galaxy.
2. The Galactic interstellar emission models
The high-energy Galactic emission is produced by the interac-tion of energetic cosmic-ray electrons and protons with interstel-lar nucleons and photons. The decay of neutral pions producedin hadron collisions accounts for most of the emission above 300MeV. Inverse Compton (IC) scattering of the interstellar radia-tion field by electrons and their Bremsstrahlung emission in theinterstellar gas are the other main contributors to the Galacticemission. The observed intensity therefore scales with the inte-gral along the line of sight of the cosmic-ray density times thegas or soft-photon one.The di ff use model used for the 3EG catalogue(Hunter et al., 1997) was based on a 3D-distribution ofmatter, cosmic-ray and soft-photon densities in the Galaxy,where the cosmic-ray density was assumed to be coupled tothe gas one over a given length scale. This length as well asthe CO -to- H HI and CO linesurveys and from kinematical distances derived for circularrotation. Distance ambiguities in the inner Galaxy were solvedby splitting the gas into the far and near sides according toits expected scale height. Gas with velocities in excess of thetangent values was attributed to the tangent point and gasemission within 10 ◦ of the Galactic center and anticenter wasinterpolated from the regions just outside these boundaries andnormalized to match the total emission seen along the line ofsight. The resulting map is, however, still strongly biased to ourside of the Galaxy, particularly for the atomic gas. This bias isreflected in the cosmic-ray density via the coupling length.For the present analyses, we have assumed an axisymmetricGalaxy for the cosmic-ray density and we have used gas column-density distributions in Galactocentric rings that are less subjectto biases due to the strategy adopted to solve the cloud distancein the inner Galaxy. The radial velocity information in the HI and CO line surveys, together with the rotation curve of Clemens(1985) and the solar motion (v =
220 km / s at R = ◦ of the Galactic center and anticenterwas interpolated as before. The all-sky Leiden-Argentina-Bonn(LAB) composite survey (Kalberla et al., 2005) was used for the HI data. Column densities, N ( HI ), were derived under the as-sumption of a constant spin temperature of 125 K. The velocity-integrated CO brightness temperature, W ( CO ), comes from theCenter for Astrophysics compilation of observations at | b | ≤ ◦ (Dame et al., 2001). The regions outside the survey boundariesshould be free of bright CO emission.We have used two di ff erent approaches to account for thecosmic-ray density gradient. One is based on the Galprop modelfor cosmic-ray propagation developed by Strong et al. (2007,2004a, 2004b), using run number 49-6002029RB to derive the γ -ray maps from pion decay, I π , bremstrahlung radiation, I brem ,and inverse Compton radiation, I IC . This version includes sec-ondary electrons and positrons, an optimized cosmic-ray spec-trum to fit the GeV excess in the EGRET data, a cosmic-raysource distribution matching the radial profile of pulsars and su-pernova remnants, a radial gradient in the X factor, and the new HI and CO gas rings.The second model, hereby referred to as the Ring model, isbased on the simpler, but realistic hypothesis that, if energeticcosmic rays uniformly penetrate all gas phases, the γ -ray in-tensity in each direction can be modelled as a linear combina-tion of gas column-densities in the di ff erent rings, plus the ICintensity map (as predicted by Galprop), and an isotropic in-tensity ( I iso ) that accounts for very local IC emission and ex-tragalactic emission. This assumption has been used to derivegas emissivities in several rings from the COS-B and EGRETdata (Strong et al., 1988, Strong & Mattox, 1996). We have re-produced these analyzes to derive gas emissivities for the new HI and CO rings using 9 years of EGRET data in three energybands ( >
100 MeV, 0 . − > ff use models.As indicated in the introduction, we have also includedin the local ring the large column-densities of ”dark” gas as-sociated with cold and anomalous dust at the transition be-tween the atomic and molecular phases (Grenier et al., 2005).This transitional phase is not traced in the radio. When remov-ing from total dust column-density maps the part that linearlycorrelates with N ( HI ) and W ( CO ), one is left with large en-velopes of excess dust around all the nearby CO clouds. Thefact that the excess dust spatially correlates with significant dif-fuse gamma radiation indicates that cosmic rays pervade gasnot accounted for in HI or CO . The gas-to-dust ratio in thisphase, as inferred from the excess dust and correlated γ -raydata, is normal. This phase appears to form an extended layerat the transition between the dense CO cores and the dens-est parts of the outer HI envelope of a cloud complex. It isbest seen in total dust maps such as the reddening E(B-V) map(Schlegel et al., 1998), or low-frequency thermal emission at 93GHz for WMAP (Finkbeiner et al., 1999), or anomalous emis-sion near 20 GHz (Lagache, 2003). We constructed a ”dark” gascolumn-density template, NH dark , by removing from the E(B-V) map the part linearly correlated with N ( HI ) and W ( CO ).This template was turned into gas column-densities by fittingit together with the N ( HI ) and W ( CO ) rings, as well as IC andisotropic components, to the all-sky γ -ray maps. Because of itscolumn-densities, clumpiness, and large spread across the sky(see Figure 4 in Grenier et al. (2005)), the ”dark” gas component ean-Marc Casandjian and Isabelle A. Grenier: A revised catalogue of EGRET γ -ray sources 3 pho t on s longitude -180 -150 -120 -90 -60 -30 0 30 60 90 120 150 180 r es i du a l s i n s i g m a -15-10-50510 Fig. 1.
The top figure is the longitude profile of all photon counts observed by EGRET above 100 MeV at all latitudes (black errorbars), compared with the di ff use counts predicted by the 3EG model (blue curve) and the Ring model (red curve). The bottom figureis the residual expressed in number of standard deviation, colors are the same as above, we added the Galprop residuals in purple.Counts from bright sources have been added to the di ff use component. For more visibility the plot are presented with a binning of4 ◦ .may strongly a ff ect source detectability. This template was alsoadded to the Galprop 49-6002029RB background model.To summarize, two di ff use backgrounds were constructedby fitting di ff erent components to the EGRET photon maps, in0 . ◦ × . ◦ bins, in the three energy bands that will be used forsource detection ( >
100 MeV, 0 . − > N pred ( l , b ) = [ P i = rings q HI , i N HI ( r i , l , b ) + P rings q CO , i W CO ( r i , l , b ) + q dark NH dark ( l , b ) + q IC I IC ( l , b ) + I iso ] × ǫ ( l , b ) + P j = sources ǫ ( l j , b j ) f j PS F ( l j , b j ) (1)2. and the Galprop model as: N pred ( l , b ) = [ q π I π ( l , b ) + q brem I brem ( l , b ) + q dark NH dark ( l , b ) + q IC I IC ( l , b ) + I iso ] × ǫ ( l , b ) + P j = sources ǫ ( l j , b j ) f j PS F ( l j , b j ) (2)In both models, ǫ ( l , b ) and f j note the EGRET exposure mapand source fluxes. The di ff use maps times the exposure wereconvolved with the EGRET PSF for an input E − . spectrum be-fore adding the source maps. The EGRET count and exposuremaps, the 3EG di ff use model, as well as the latest instrumentresponse functions, were downloaded from the CGRO ScienceSupport Center. They di ff er from those used for 3EG sincethey were reprocessed in 2001. The q parameters (gas emissiv-ities or relative contributions of di ff erent radiation components) were fitted to the data by means of a maximum likelihood withPoisson statistics. To avoid biasing the interstellar parameters,the model included the brightest sources detected during a firstsource detection iteration with a significance > σ , with fixedfluxes. Changing these fluxes within their statistical uncertain-ties do not significantly change the di ff use results.The resulting emissivities corresponding to the local gas arefully consistant with Grenier et al. (2005) Table 1. The emissivitygradient in the Galactic plane will be described in a separate pa-per. The quality of the fit can be seen in Figure 1. The top figuredisplays the longitude profile of all the EGRET photon countsabove 100 MeV. The error bars are only statistical. The plot com-pares the best fit that can be obtained using the former 3EG dif-fuse model with the longitude profile resulting from the presentRing model. The bottom plot shows the longitude profile of theresiduals and the improvement of the ring model over the 3EGone. It also shows the residuals for the best fit Galprop model.All modelled profiles include the brightest sources. Systematicdi ff erences can be seen in various places where the 3EG modelsignificantly over-predicts and under-predicts the data while thenew models behave better. Because of its larger flexibility (thegas emissivity gradient due to cosmic-ray variations is measured,not inferred from propagation properties or gas coupling), theRing model was found to best fit the data. It is worth noting thaneven if the agreement is excellent, there still exists small devia- Jean-Marc Casandjian and Isabelle A. Grenier: A revised catalogue of EGRET γ -ray sources Fig. 2.
Map in Galactic coordinates of the residuals (expressed in σ = p N pred values) between the E >
100 MeV photon counts(in 0.5 ◦ bin) and the best fit with the Ring model using Equation(1) . tions that can significantly impact source detection and charac-terization.The residual count map obtained above 100 MeV with theRing model is presented in Figure 2. It displays the statistical dif-ference ( N obs − N pred ) / p N pred between the observed counts andthose predicted from the di ff use background and bright sourcesusing equation 1. The model globally fits very well the data. Theextended blue fan-like structures with negative residuals are cor-related with the edge of several observing periods. They prob-ably result from a wrong exposure estimate at large angle fromthe instrument axis. They are visible independently of the choiceof di ff use model (Ring, Galprop, or 3EG). Their spatial extent islarge enough compared to the PSF size not to severely a ff ectsource detection, yet source fluxes in these directions are under-estimated. Uncertain knowledge of the o ff -axis instrument ex-posure is also reflected in the small model deficit (orange edge)bordering the fan-like excesses. We have checked for suspiciousstrings of faint sources that would correlate with these instru-mental features.The use of two di ff erent background models allowed usto study their impact on source detection and characterization.Given its higher likelihood value and locally flatter residuals,the Ring model was used to derive the default source flux andlocation. The values obtained with the Galprop background areused to illustrate the amplitude of the systematic uncertainty dueto the background modelling. When searching for sources weused the di ff use emission parameters calculated from this globalfit. We adjusted a source flux together with a free normaliza-tion of the total di ff use flux within 15 ◦ around each pixel, and afree isotropic flux. This procedure is the same as used for 3EG(Gmult and Gbias). These two parameters correct for small lo-cal mismatches between the di ff use model and the data. Gmultfluctuates around 1.
3. Source detection
As for the derivation of the 3EG catalogue, we have used theLIKE code (Mattox, 1996, version 5.61) to compute the 2-dimension binned Poisson likelihood of detecting a source at aparticular location on top of the di ff use background. LIKE cal- culates the Test Statistic ( T S ) value that compares the likelihoodof detecting a PSF-like excess above the background to the nullhypothesis - a random background fluctuation - for a given po-sition. The likelihood ( L i ) is calculated as the product, for allpixels within 15 ◦ of a specific position, of the Poisson probabil-ities of observing photons in a pixel where the number of countsis predicted by the model (background + source). The likelihoodratio test statistic is defined as T S = − LnL − LnL ), wherethe likelihood values L and L are respectively optimized withand without a source in the model. Asymptotically, the T S dis-tribution follows a χ one. The detection significance of a sourceat the given position is √ T S σ (Mattox 1996).Sources have been searched for in the summed maps corre-sponding to cycle 1, 2, 3, 4, 1 +
2, 3 +
4, 1 + + +
4, 5 +
6, 7 + + + + + + + + + +
9. In addition, we have analyzed the 46individual periods listed in Table 1 for which flaring 3EG sourceshad been detected. As for the summed maps, the individual pe-riod maps retained only photons with inclinations within 30 ◦ from the instrument axis, or 19 ◦ for cycle 6, 7, 8, and 9. Photonsand exposure maps were binned to 0 . ◦ × . ◦ .To build the 3EG catalogue, sources were detected only inthe integrated E >
100 MeV band.
T S maps were then con-structed in three energy bands ( >
100 MeV, 0 . − > T S and a source final position was obtained from the smallest er-ror contours. Given the modern computer performance, we havedirectly searched for sources independently in the three energybands.At 100 MeV, the EGRET PSF is wide and there exists dis-crepancies between its real shape, as observed in bright sources,and the modelled one. In practice, di ff erences may also comefrom a more complex source spectrum than the single power-law assumed to integrate the PSF. A choice of 300 MeV insteadof 100 MeV for the lower analysis threshold might have been abetter trade-of between count rates for detection and systematicuncertainties in the PSF. We have, however, kept a lower limitof 100 MeV as in 3EG in order to account for soft sources andto allow comparison with the 3EG results. We have assumed aspectral index of 2.0 for all sources but for 11 bright ones whichhad a 3EG spectral index far from 2.0. For the latter, we haveused their 3EG index to integrate the PSF.Each of the 10 all-sky summed maps was divided, both inGalactic and equatorial coordinates, in 45 zones with a largeoverlap. The use of both coordinates systems is required sincesource images are deformed in rectangular projection at highlatitude or declination. For each zone, each individual period,and each of the 3 energy bands ( >
100 MeV, 0 . − > T S map for excesses above the back-ground. Sources were iteratively detected from high
T S to low
T S in successive
T S maps. Between each steps, the detectedsources were included in the background model until no ex-cess with √ T S > T S map. An exam-ple of the iteration around Geminga is given in Figure 3. Peaksin the
T S map were automatically detected with SExtractor(Bertin & Arnouts, 1996) and converted into source position bytaking the
T S -weighted centroid in the region enclosed by the95% confidence contour around this position. Source positionswere recalculated at each iteration to take into account the in-fluence of the neighbouring sources. More than 1100
T S -mapswere thus calculated at the CCIN2P3 Computing Center. ean-Marc Casandjian and Isabelle A. Grenier: A revised catalogue of EGRET γ -ray sources 5 Table 1.
List of individual or short periods used in the analysis in addition to the summed cycles.
Name Sum of viewing periods Name Sum of viewing periods Name Sum of viewing periods2 + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + Fig. 3.
An example of the iterative source detection with the 2Dbinned likelihood around Geminga at energies above 100 MeV. 4consecutive
T S maps are shown. Sources are detected, then areincluded in the background for the next step until no significantone is left. The colourbar gives
T S .
4. Catalogue construction
To account for real versus modelled PSF discrepancies in ex-tremely bright sources, for instance to account for the splittingin two of the bright pulsar sources or for the artifacts in theVela tails, we have removed all the source candidates within 3 . ◦ of the intense sources (that exhibit more than 800 photons in amap). For less intense sources, we have checked the probabilityof having a double versus single source with a specific likeli- hood calculation, using the likelihood ratio between the 2 casesto keep or reject the double source.At the end of this stage, most sources have two possible po-sitions per energy band and observation, one from the Galacticcoordinate map and one from the equatorial one. We cross-compared the two and selected the position from the least de-formed projection. Sources detected only once were not includedin the list unless their latitude or declination were higher than 40 ◦ or their longitude or right-ascension were less than 5 ◦ from themap edges.At this stage, most sources have three possible positions(with energy) for a given observation. We chose among the threethe position corresponding to the smallest 95% confidence con-tour, unless its peak √ T S were 1.5 smaller than found in ananother energy band. The latter condition reduces the risk of in-correct source assignment during the cross-comparison phase.Sources found at low energy, but not at high energy were in-cluded in the list, as well as sources found only at high energy.We have used the same criteria to cross-compare the sourcepositions for individual periods and summed cycles in order toobtain a final list of candidate sources with the best positionfrom the di ff erent energy bands and periods / cycles. We followedthe whole procedure with both the Ring and Galprop interstellarbackgrounds. We obtained respectively 1192 and 1225 candi-date sources with the Ring and Galprop models. Source fluxesand √ T S values above 100 MeV were calculated for these setsof positions for the di ff erent periods and cycles. Unlike in 3EG,we did not adjust the position of the identified sources (AGN orpulsars) to that of their radio counterpart.We adopted the same detection threshold as for the 3EG cat-alogue ( √ T S > | b | < ◦ and √ T S > T S maps of allthe sources that barely passed the detection threshold with theRing model and had √ T S ∼ ff er-ent energy bands and time periods can strongly a ff ect the cataloglist near the detection threshold. Several strategies were testedbefore adopting the present one, but one must remember thata faint source can pass or drop below the threshold by slightlychanging its position or that of its neighbours. Given the steepincrease in source numbers with decreasing T S , we also empha-size that a small change in the
T S threshold, alternatively in the
Jean-Marc Casandjian and Isabelle A. Grenier: A revised catalogue of EGRET γ -ray sources background over which the source T S is calculated, results ina large change in the number of catalogue entries. For instance,lowering the √ T S threshold by 0.1 would add 27 sources.
5. Catalogue description
The EGR acronym has been adopted for the EGret Revisedsource list presented in Table 2 and Table A.1 in a format similarto the 3EG one. As explained above, the source characteristics(position and flux, and their uncertainties) have been determinedwith the Ring model because of its higher flexibility, better fit,and flatter residual map. A secondary position and flux has beenmeasured with the Galprop model and is listed in Table 2 andTable A.1 to illustrate the amplitude of the systematic uncertain-ties due to the choice of interstellar model.Sources found within a radius of 1.5 PSF FWHM from a verybright source, and / or with very asymmetric T S map contours arenot included in Table 2 and Table A.1. Still, they represent sig-nificant excesses of photons above the background which maybe due to extended sources, or structures not properly modelledin the interstellar emission, or artifacts due to incorrect PSF tails.This list of 14 confused sources is given in Table B.1, under theacronym EGRc for EGret Revised confused.For both tables, the description for each column follows:1. Num: source number in order of increasing right ascension.2. Name: source name based on J2000 coordinates.3. RA and Dec: J2000 equatorial coordinates in degrees.4. l and b: Galactic coordinates in degrees.5. θ : angular radius, in degrees, of a circular cone which con-tains the same solid angle as the 95% confidence contour.6. F: flux in 10 − photon cm − s − for E >
100 MeV and foreach time period.7. σ F : 1 σ statistical flux uncertainty in 10 − photon cm − s − .8. Cnts: number of photons detected with E >
100 MeV.9. √ T S : statistical significance of the detection.10. vp: short viewing period as defined in Table 1 or summedcycles noted px for cycle x, pi jkl for the sum of cycles i, j,k, and l, and p
19 for the total of 9 cycles.11. l sys and b sys : Galactic longitude and latitude obtained withthe Galprop background model.12. F sys : flux obtained with the Galprop background model, in10 − photon cm − s − .13. 3EG: third EGRET catalog counterpart source name if oneexists within a radius of 1 PSF FWHM (2 ◦ for E >
100 MeV)from the EGR source and if the nearest neighbour relationbetween the EGR and 3EG sources is univocal (the nearestneighbour of the EGR source is the 3EG one and vice versa).
6. Comparison with the 3EG catalogue
The revised catalogue contains 174 sources plus 14 confusedsources compared to the 265 entries of the 3EG catalogue (ex-cluding the Vela artifacts). Their spatial distribution across thesky looks di ff erent from that of the 3EG sources, as illustrated inFigures 4 and 5. The accumulation of faint 3EG sources within30 ◦ of the Galactic center is much more reduced in the new re-sults and fewer sources are seen below 30 ◦ in general. Thesechanges at low and mid latitudes are primarily due to the in-crease in background intensity from new HI , CO , and dark gasstructures. At high latitude, the use of more γ -ray observationsand of a revised large-scale IC component in the backgroundmay also explain why a handful of 3EG sources have fallen be-low the detection threshold whereas new ones are now detected. −200−150−100−50050100150200−100−80−60−40−20020406080100 Fig. 4.
Spatial distribution, in Galactic coordinates, of the EGRsources. The confused sources are marked as open circles. −200−150−100−50050100150200−100−80−60−40−20020406080100
Fig. 5.
Spatial distribution, in Galactic coordinates, of the 3EGsources. −200−150−100−50050100150200−100−80−60−40−20020406080100
Fig. 6.
Spatial distribution, in Galactic coordinates, of the 3EGsources with no counterpart in EGR: the unidentified sources ascircles and the identified AGN as stars. The filled circles andstars mark the sources that were flagged as extended or confusedin the 3EG catalogue.The names of the 107 unconfirmed 3EG sources are listed inTable 3 and they are displayed in Figure 6. They comprise onlysix sources that had been firmly identified as AGN by Hartmanet al. (1999), but that had been flagged as extended or con-fused by the EGRET team. In fact, the proportion of these ex-tended or confused cases among the unconfirmed 3EG sourcesis overwhelming (95%) and significantly larger than among theconfirmed ones. The unconfirmed and confirmed 3EG groupsrespectively show 69% and 33% of possibly extended ’em’sources. Figure 6 also shows that the vast majority of uncon-firmed 3EG sources were unidentified and spatially correlatedwith the Gould Belt system of nearby clouds. They follow thecharacteristic trace of the inclined Belt across the sky, gatheringat | b | < ◦ , more at positive latitudes toward the Galactic centre ean-Marc Casandjian and Isabelle A. Grenier: A revised catalogue of EGRET γ -ray sources 7 Table 2.
The EGR catalogue. The three first sources are shown. The full catalogue is available with the on-line version
Num Name RA Dec l b θ F σ F Cnts √ TS vp l sys b sys F sys + + + −200−150−100−50050100150200−100−80−60−40−20020406080100 new EGR sources confused Fig. 7.
Spatial distribution, in Galactic coordinates, of the newEGR sources with no 3EG counterpart. The confused sourcesare marked as open circles.and below the plane in the anticenter. The EGR source sky dis-tribution in Figure 4 does not exhibit the Gould Belt signatureanymore.The fact that many 3EG sources are not confirmed in thepresent analyses should not cast doubts on the detection methodfrom a statistical point of view. They did correspond to signif-icant photon excesses above the background in the 3EG analy-ses, but, in the absence of some structures in the predicted inter-stellar background, an ensemble of point sources with the wideEGRET PSF would compensate for the missing clouds and yieldan excellent fit to the data. Figure 8 illustrates this point with theunidentified source 3EG J0556 + σ in 3EG.The left side shows the TS-map corresponding to the secondstage of the iterative source detection around Geminga above100 MeV. It is the same as in Figure 3 but we have used here the3EG di ff use emission model instead of the Ring one. The samesources are detected except for 3EG J0556 + ff use emission appearsin the ratio of the Ring to 3EG background intensities (Figure8, right). The photons attributed to a point source in 3EG wherein fact coming from a gas cloud in the Galaxy.
This is prob-ably still the case in the present analysis, although to a lesserdegree, in particular at very low latitude where optical thickness
Table 3.
Names of the 3EG sources with no EGR counterpart + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + in HI and CO severely limits our knowledge of the true column-densities. Other sources may also be due to increased cosmic-raydensities in specific clouds with respect to the local Galactic av-erage. Over-irradiated clouds near cosmic-ray sources would be Jean-Marc Casandjian and Isabelle A. Grenier: A revised catalogue of EGRET γ -ray sources Table 4.
Names of the new EGR sources with no 3EG counter-part
EGR J0028 + + + + + + + + + + + + + + + + Fig. 8.
Second stage of the iterative source detection aroundGeminga (see Figure 3) obtained using the 3EG model (left)and map of the Ring model intensity divided by the 3EG one(right). The excess in the TS map assigned in 3EG to the 3EGJ0556 + ff use emission in the 3EG model. Maps are given in 0.5 ◦ bins and galactic coordinates |F EGR −F |/ σ F Fig. 9.
Histogram of the relative flux di ff erences | F EGR − F EG | /σ F EGR measured between the EGR and 3EG counterpartsin units of the statistical error on flux for each source. All fluxesare measured above 100 MeV.detected as a single or cluster of point sources, depending ontheir angular scale.For the 81 EGR sources that do have a 3EG counterpart, wefind a reasonable agreement in position and flux from both anal-yses. On average, we find 3% lower fluxes in the EGR analysiswith respect to the 3EG one because of the increase in Galacticbackground. Figure 9 shows the histogram of ratios of the EGRand 3EG flux di ff erence over the statistical error on flux for each ∆ θ / θ Fig. 10.
Histogram of the relative angular separation between thepositions found for the EGR and 3EG counterparts in units of the95% confidence angle for each source. |F EGR −F syst |/ σ F Fig. 11.
Histogram of the relative flux di ff erences | F EGR − F sys | /σ F EGR measured with the Ring and Galprop models in unitsof the statistical error on flux for each source. All fluxes are mea-sured above 100 MeV.source: | F EGR − F EG | /σ F EGR . The EGR flux was taken for theobservation with highest √ T S and compared to the 3EG coun-terpart flux for the same time period if available. Average P19fluxes were compared to the 3EG P1234 average for non flaringsources. The flux di ff erences are modest (17% rms dispersion)and in most cases smaller than the statistical uncertainties onflux estimates. Similarly, Figure 10 shows that the angular sepa-rations between EGR and 3EG counterparts are often consistentwith the θ error radii. Yet, thirty sources have been found asfar as 0 . ◦ from the 3EG position and this will greatly impactcounterpart searches and identification at other wavelengths.On the other hand, we find 30 new EGR sources with no3EG counterpart. Their names are listed in Table 4 and they aredisplayed in Figure 7. Most of them are detected just above thethreshold and 11 of them were indeed present in the 3EG com-plementary list, just below the significance threshold.
7. EGR source distributions and potentialcounterparts
Because of the new gas data we have used at intermediate lati-tude, the comparison between the EGR and 3EG source charac-teristics allows to judge, to some extent, the impact of our limitedknowledge of gas mass tracers. The comparison between the fluxand positions obtained with the Ring and Galprop models givesan estimate of the systematic uncertainties due to our limitedknowledge of the true cosmic-ray distribution across the Galaxy. ean-Marc Casandjian and Isabelle A. Grenier: A revised catalogue of EGRET γ -ray sources 9 ∆ θ syst / θ Fig. 12.
Histogram of the relative angular separation between thepositions found with the Ring and Galprop models in units of the95% confidence angle for each source.Figure 11 and Figure 12 show that, in most cases, the di ff erencesare smaller than the statistical uncertainties. The distribution of95% confidence radii peaks between ∼ . ◦ and ∼ . ◦ . Theuncertainty in the background induces an additional systematicerror of ∼ . ◦ for most sources. It should be kept in mind whilelooking for counterparts.We have searched the EGR error circles for poten-tial counterparts of interest such as pulsars from theATNF catalogue (Manchester et al., 2005), blazar candidatesfrom the ASDC list (Massaro et al., 2005) and the CGRaBSlist (Healey et al., 2008), other flat radio sources from theCRATES compilation (Healey et al., 2007), supernova rem-nants from the Green catalogue (Green, 2006), OB associations(Mel’Nik & Efremov(1995)), and X-ray and TeV pulsar windnebulae (Li et al. (2008) and Grenier, 2008). The results are dis-played in Figure 13. We have found 13 radio pulsar associa-tions in addition to the 6 objects firmly identified by EGRET.Thirteen EGR sources coincide with supernova remnants, 9 withpulsar wind nebulae, 7 with OB associations, 53 with blazarcandidates, and 19 with other flat radiosources. These associa-tions should not be considered as identification, but as spatialcoincidences worthy of further investigations, in particular withthe improved angular resolution of GLAST. Yet, they reveal thatas many as 87 sources have no obvious counterpart among thewell-known γ -ray emitters despite the large number of pulsars(1775) and radiosources (11 000) that were cross-correlated withthe sources and that spread across the entire sky and along theGalactic plane. The lack of blazar counterparts is all the moresurprising that the spatial distribution of the sources o ff the planeis quite reminiscent of an isotropic, therefore extragalactic, dis-tribution. The latitude distribution, shown in Figure 14, is quiteconsistent above 30 ◦ with a sample drawn from a uniform pop-ulation according to the exposure map, as shown by the blackcurve. The distribution flattens at lower latitude because of theincreased background that drastically limits the survey sensitiv-ity. Studying the consistency with an extragalactic populationat medium latitudes and the implication of the lack of a flat ra-diosource is beyond the scope of this paper and will be addressedin a separate one. The sharp peak below 3 ◦ in latitude indicatesyoung emitters. Their clustering in the inner Galaxy ( l ≤ ◦ ),toward the direction tangent to the Carina arm, and toward theCygnus region outlines their close relationship to large molec-ular complexes and star forming regions at a distance of a fewkpc. latitude (deg) Fig. 14.
Latitude distribution of the EGR sources with youngGalactic sources at | b | < ◦ , nearly isotropically distributedsources far from the plane, as expected from the black curve,and a flattening at mid-latitude because of the rapid increase inthe interstellar background flux. Fig. 15.
T S -map obtained at energies above 1 GeV toward theGalactic center above the 3EG (a) and Ring (b) interstellar model
8. Discussion on specific sources
There is considerable interest in the physical processes occurringin the Galactic center region. The 3EG catalogue lists one sourcelocated toward the Galactic center, 3EG J1744-3011. We findtwo point sources in this region, EGR J1740-2851 at l = − . ◦ , b = . ◦ and EGR J1747-2852 at l = . ◦ , b = − . ◦ . Figure15 display the T S -map for photons with energies above 1 GeVabove the 3EG and the Ring background models. The θ errorradius around EGR J1740-2851 and EGR J1747-2852 formerlyexcludes the Galactic Center but source locations and fluxes inthis direction should be taken with extreme caution since thehigh gas optical depth around the Galactic center and the ve-locity pile-up toward the center induce large uncertainties in thetotal gas column densities.Coincidences with supernova remnants were noted(Sturner & Dermer(1995)) and are confirmed in the presentanalysis (see Table 5), but several also host a pulsar windnebula, as in CTA 1 and IC 443, so we need much higher γ -ray sources −200−150−100−50050100150200−100−80−60−40−20020406080100 Fig. 13.
The revised EGRET source catalog, shown in Galactic coordinates. The symbols indicate the counterpart types found inthe error box: identified pulsars as black squares; other ATNF pulsars as open squares; LSI +
61 303, LMC, and solar flare asblack triangles; ASDC and CGRaBS blazar candidates as black diamonds; other flat-spectrum radio-sources from CRATES as opendiamonds; supernova remnants from the Green catalogue as stars; no counterpart as crosses.
Table 5.
Names of the sources and supernova remnants found inspatial coincidence
EGRJ0008 + + + + + + + + + + γ CygniEGRJ2227 + + + + resolution γ -ray images to identify the origin of the emission,especially in these crowded regions. EGRET detections areconfirmed toward two TeV-emitting wind nebulae aroundPSR J1420-6048 (in Kookaburra, EGRJ1418-6040) and PSRJ1826-1334 (EGRJ1825-1325). Another interesting candidate isthe wind nebula of the 11-kyr old and very energetic pulsar PSRJ2229 + + ◦ between the new EGR J0028 + + ff due to pair production attenuation occurs at high energy.They are therefore good candidate for accelerating particles tohigh energies. Harding et al. (2005) has predicted a γ -ray fluxfor PSR J0030 + γ -ray millisec- Fig. 16.
Likelihood TS contours for energies above 100 MeVand periods incompassing PSR J0030 + + + ◦ ffi cient particleacceleration in compressed or shocked pulsar winds, as well asin microquasar jets. Inverse Compton scattering of the brightstellar radiation would dominate at GeV energies. We find nointeresting EGRET counterpart to these high-energy objects, butfor the LSI + ◦
303 radiosource. The latter had long been as-sociated with the COS-B source 2CG 135 +
01 and the EGRET ean-Marc Casandjian and Isabelle A. Grenier: A revised catalogue of EGRET γ -ray sources 11 +x
3C 345MRK 501
65 64 63 62 61 galactic longitude g a l ac ti c l a tit ud e
4C +38.41
Fig. 17.
Likelihood TS contours ( 50%, 68%, 95% and 99% con-fidence) for energies above 100 MeV and period 5190. The crossis the EGR catalog position, the plus sign the position with max-imum likelihood and the black dots mark the radio positions of3C345, Mrk 501, and 4C + + ff en et al., 1997), yet it had movedout of the 3EG error box and the marginal γ -ray variability couldnot be associated with the radio flux variations. In the presentanalysis, we find the radiosource very near the centre of the EGRJ0240 + / X-ray binary, AO 0535 +
26, both proposed as3EG counterparts (Combi et al., 2003, Romero et al., 2001).Another noticeable new source is EGR J1642 + σ rather close to 3C345. 3C345 is one of the mostprominent flat spectrum ( α = − .
1) radio-loud, superluminalsources and is therefore an excellent candidate for a γ -ray blazar.EGRET has viewed this region 12 times, in particular duringperiod 5190 when a flare was found. We have analyzed againthis particular period with the Ring model since it had not beenused in the overall detection search. Figure 17 shows the result-ing TS contour for photons with energies above 100 MeV thatis well centered on 3C345. The cross corresponds to the EGRposition (period 5190), the plus sign to the position with maxi-mum likelihood and the black dots to the position of 3C345 anda nearby AGN. A marginal detection was also obtained for pe-riod 3034 at a level of 2.1 σ . It should, however, be noted thatthe small photon excess above 500 MeV has been attributed toa flare from Mrk 501 by Kataoka et al. (1999) because the cen-troid was closer to the famous TeV source, so the association ofEGR J1642 + γ rays at largeangle from the strongly beamed emission from the jet. We donot, however, confirm the spatial coincidence with EGR sourcesin the present work. All these galaxies lie well beyond the 95%confidence region of EGR sources.
9. Conclusions
We have searched for point-like sources in the reprocessedEGRET data from cycle 1 to 9 using new interstellar backgroundmodels based on the most recent HI , CO , and dark gas data, aswell as two di ff erent assumptions for the cosmic-ray distribution(the GALPROP di ff usion model or a radial emissivity gradientfitted to the di ff use EGRET data). We have used the 3EG tools,likelihood method, procedure and significance threshold to de-tect sources, but have expanded the search to 3 di ff erent energybands (above 100 MeV, 0.3-1 GeV, and above 1 GeV). The re-sulting number of detected sources has decreased by more than athird. Many unidentified sources, in particular among those spa-tially associated with the Gould Belt, are not confirmed as signif-icant excesses. Their emission can be explained by the additionalinterstellar emission and its structure. Several interesting coun-terparts to 3EG sources, such as radiogalaxies, massive binaries,and microquasars, are now found outside the 95% confidenceregion. We have cross-correlated the new source positions withlarge pulsar, supernova remant, pulsar wind nebulae, OB asso-ciations, and radiosource catalogues, yet half the sample has noattractive counterpart among the potential γ -ray emitters. 30 newpossible γ -ray sources have also been found.This EGR catalog will be available infits format at the Strasbourg astronomicalData Center (CDS) and in ASCII format athttp: // / EGRET catalogue / home.html Acknowledgements.
We are deeply grateful to Bob Hartman for his helpful ex-planations about the construction of the 3EG catalogue, and to Seth Digel andAndy Strong for their help with the gas and Galprop maps.
References
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Online Material ean-Marc Casandjian and Isabelle A. Grenier: A revised catalogue of EGRET γ -ray sources , Online Material p 2
Table A.1.
The EGR catalogue
Num Name RA Dec l b θ F σ F Cnts √ TS vp l sys b sys F sys + + + + + + + + + ean-Marc Casandjian and Isabelle A. Grenier: A revised catalogue of EGRET γ -ray sources , Online Material p 3 + + + + + + + + + + + + + ean-Marc Casandjian and Isabelle A. Grenier: A revised catalogue of EGRET γ -ray sources , Online Material p 4 +
23 EGR J0423 + + + + + +
26 EGR J0433 + + + + + + -172.53 -20.33 94.4 3EGJ0450 + + ean-Marc Casandjian and Isabelle A. Grenier: A revised catalogue of EGRET γ -ray sources , Online Material p 5 + + + + + + + + + + +
36 EGR J0531-2934 82.90 -29.57 -126.68 -29.29 1.00 32.8 11.4 21 4.1 3355 -127.33 -27.00 23.3 3EGJ0531-29409.6 4.8 19 2.5 p39.9 4.3 28 2.8 p346.3 2.7 32 2.7 p12346.2 2.7 32 2.7 p1918.1 7.1 22 3.4 335 + +
37 EGR J0534 + + + + +
38 EGR J0537-6946 84.33 -69.78 -79.73 -31.71 0.39 11.9 2.0 175 7.0 p19 -79.82 -31.76 12.1 3EGJ0533-69169.1 2.6 74 4.1 p118.8 8.0 22 2.9 p26.7 6.6 8 1.2 p3 ean-Marc Casandjian and Isabelle A. Grenier: A revised catalogue of EGRET γ -ray sources , Online Material p 6 + + + + + + + +
43 EGR J0617 + + + + + + + +
45 EGR J0633 + + + ean-Marc Casandjian and Isabelle A. Grenier: A revised catalogue of EGRET γ -ray sources , Online Material p 7 +
46 EGR J0722-5121 110.60 -51.36 -97.22 -16.34 0.45 7.9 2.1 107 4.2 p1234 -97.02 -16.25 8.2 3EGJ0725-51409.7 2.9 73 3.9 p19.1 4.3 33 2.4 p39.0 2.8 73 3.7 p125.8 3.2 31 1.9 p347.8 2.1 105 4.1 p1920.5 7.2 37 3.4 338547 EGR J0723 + + +
48 EGR J0726-4715 111.74 -47.26 -100.78 -13.98 0.50 16.7 3.6 113 5.4 p1 -100.82 -14.73 17.7 3EGJ0724-471315.6 3.4 114 5.2 p1210.1 2.5 124 4.5 p12349.7 2.5 120 4.4 p1949 EGR J0737 + + + + + + + +
52 EGR J0807 + + +
53 EGR J0812-0624 123.11 -6.41 -131.70 14.79 0.70 20.6 4.6 73 5.5 p19 -131.77 14.79 18.6 3EGJ0812-064621.5 5.3 60 5.1 p1129.8 86.1 5 2.4 p421.5 5.3 60 5.1 p1222.3 5.3 63 5.3 p123414.7 10.3 10 1.7 p5618.1 7.3 25 3.0 44054 EGR J0829 + + + + + + ean-Marc Casandjian and Isabelle A. Grenier: A revised catalogue of EGRET γ -ray sources , Online Material p 8 +
57 EGR J0834-4512 128.70 -45.21 -96.48 -2.88 0.03 747.9 10.9 9417 101.8 p19 -96.49 -2.87 785.9 3EGJ0834-4511730.8 14.5 5101 75.5 p1699.8 41.5 616 24.2 p2762.6 19.5 3073 58.6 p3874.4 57.5 467 22.7 p4727.0 13.7 5713 78.9 p12773.2 18.5 3528 62.5 p34744.1 11.0 9244 100.8 p123491.5 9.1 186 15.7 p789777.6 23.7 2154 49.4 338558 EGR J0852-1224 133.24 -12.40 -120.77 19.98 0.87 41.2 11.1 36 5.1 440 -121.16 19.39 41.7 3EGJ0852-121614.2 4.4 43 4.0 p114.2 4.4 43 4.0 p1213.5 4.3 41 3.8 p123413.0 4.3 40 3.7 p1959 EGR J0853 + + + + +
62 EGR J0956 + + + + + + + + + ean-Marc Casandjian and Isabelle A. Grenier: A revised catalogue of EGRET γ -ray sources , Online Material p 9 + + + + + ean-Marc Casandjian and Isabelle A. Grenier: A revised catalogue of EGRET γ -ray sources , Online Material p 10
76 EGR J1222 + + + + + + + + ean-Marc Casandjian and Isabelle A. Grenier: A revised catalogue of EGRET γ -ray sources , Online Material p 11
83 EGR J1259-2209 194.92 -22.16 -54.55 40.67 0.58 8.6 2.0 128 4.9 p19 -54.63 40.60 8.09.6 3.7 43 3.0 p13.2 3.0 15 1.1 p220.4 8.2 23 3.1 p38.9 4.3 27 2.4 p46.2 2.4 58 2.9 p1212.2 3.9 51 3.7 p348.0 2.0 108 4.5 p123413.5 7.5 19 2.1 p5617.9 11.4 9 2.0 204026.6 10.0 24 3.4 virgo3a84 EGR J1309-0535 197.29 -5.59 -48.96 57.00 0.32 6.9 1.6 189 4.9 p19 -48.28 57.28 7.9 3EGJ1310-051712.1 3.8 78 3.5 p15.1 3.2 19 1.8 p24.2 3.8 16 1.2 p36.1 2.9 34 2.3 p49.9 2.7 100 4.1 p125.0 2.3 47 2.3 p347.6 1.8 149 4.7 p12347.5 3.5 48 2.3 p566.9 3.8 20 2.1 virgo29.2 6.2 10 1.8 204085 EGR J1314-3417 198.58 -34.30 -51.70 28.33 0.45 12.6 2.3 156 6.3 p1234 -51.69 28.20 13.1 3EGJ1314-343115.8 4.6 58 4.1 p115.9 3.9 78 4.8 p28.9 5.2 17 2.0 p415.6 3.0 134 6.2 p126.3 3.5 24 2.0 p3412.6 2.3 156 6.3 p1986 EGR J1328-4337 202.07 -43.62 -50.04 18.75 0.37 10.5 2.5 144 4.8 p1234 -50.04 18.75 10.8 3EGJ1324-43145.1 4.2 23 1.3 p114.4 4.4 64 3.7 p210.3 5.1 29 2.3 p37.2 6.2 14 1.2 p410.5 3.1 94 3.8 p1210.0 4.0 48 2.8 p3410.5 2.5 144 4.8 p1915.9 7.6 22 2.4 314 +
87 EGR J1337-1310 204.45 -13.17 -40.02 48.16 0.63 30.2 6.5 82 5.7 p56 -39.34 47.22 26.5 3EGJ1339-141915.2 8.9 14 2.0 p39.3 3.5 43 3.0 p410.5 3.3 58 3.7 p342.6 1.8 36 1.5 p123438.2 20.3 12 2.3 p7897.2 1.9 124 4.3 p195.4 5.0 9 1.2 virgo223.8 10.3 16 3.1 204017.6 8.0 19 2.7 virgo3a88 EGR J1338 + + + + ean-Marc Casandjian and Isabelle A. Grenier: A revised catalogue of EGRET γ -ray sources , Online Material p 12 +
92 EGR J1418-6040 214.72 -60.68 -46.56 0.40 0.22 68.7 11.9 369 6.2 p34 -46.32 0.38 58.1 3EGJ1420-603820.0 13.3 76 1.5 p164.7 15.1 218 4.5 p373.5 19.2 147 4.1 p415.3 12.0 71 1.3 p1243.7 8.5 439 5.4 p123442.9 8.5 431 5.3 p1953.7 24.3 63 2.3 23059.5 17.2 152 3.7 314 +
93 EGR J1424 + + + + + + + + + ean-Marc Casandjian and Isabelle A. Grenier: A revised catalogue of EGRET γ -ray sources , Online Material p 13 + + + + + + ean-Marc Casandjian and Isabelle A. Grenier: A revised catalogue of EGRET γ -ray sources , Online Material p 14 + + + + + + + + ean-Marc Casandjian and Isabelle A. Grenier: A revised catalogue of EGRET γ -ray sources , Online Material p 15 + + + + + + + + -8.65 -8.43 72.4 3EGJ1800-395519.1 5.9 103 3.5 p311.1 4.6 88 2.5 p3425.9 13.9 27 2.1 p563.9 2.7 75 1.5 p1928.4 25.8 10 1.2 223042.3 22.0 18 2.3 229 + ean-Marc Casandjian and Isabelle A. Grenier: A revised catalogue of EGRET γ -ray sources , Online Material p 16 + + + + + + + +
128 EGR J1814-6423 273.64 -64.39 -29.98 -20.46 0.41 14.6 3.9 66 4.5 p1234 -29.97 -20.43 15.5 3EGJ1813-641917.4 5.8 40 3.7 p119.1 8.8 18 2.8 p213.9 8.7 12 1.9 p315.7 4.7 51 4.0 p1211.9 7.1 15 2.0 p3414.5 3.9 65 4.4 p19129 EGR J1820-7920 275.16 -79.35 -45.39 -25.22 0.44 24.4 5.8 63 5.3 p12 -45.40 -25.24 23.3 3EGJ1825-792622.2 6.6 40 4.3 p127.0 11.5 21 2.9 p220.2 10.2 16 2.4 p318.8 4.4 74 5.2 p123418.7 4.4 73 5.2 p19130 EGR J1822 + + + + ean-Marc Casandjian and Isabelle A. Grenier: A revised catalogue of EGRET γ -ray sources , Online Material p 17 + + + + + + + + + + ean-Marc Casandjian and Isabelle A. Grenier: A revised catalogue of EGRET γ -ray sources , Online Material p 18 + +
146 EGR J1959 + + + + + + + + ean-Marc Casandjian and Isabelle A. Grenier: A revised catalogue of EGRET γ -ray sources , Online Material p 19 + + + + + + + + + + + + + ean-Marc Casandjian and Isabelle A. Grenier: A revised catalogue of EGRET γ -ray sources , Online Material p 20 + + + + + + + + + + ean-Marc Casandjian and Isabelle A. Grenier: A revised catalogue of EGRET γ -ray sources , Online Material p 21 + + + + + + + ean-Marc Casandjian and Isabelle A. Grenier: A revised catalogue of EGRET γ -ray sources , Online Material p 22
Table B.1.
The EGR confused sources catalogue
Num Name RA Dec l b θ F σ F Cnts √ TS vp l sys b sys F sys + + + + + + + + ean-Marc Casandjian and Isabelle A. Grenier: A revised catalogue of EGRET γ -ray sources , Online Material p 23 + + + + + + + + + ++