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EGRCAT - CGRO/EGRET Revised Catalog of Gamma-Ray Sources

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Overview

The CGRO/EGRET Revised Catalog of Gamma-Ray Sources (EGR) is a catalog of point gamma-ray sources detected by the EGRET detector on the Compton Gamma Ray Observatory. The authors used the entire EGRET gamma-ray dataset of reprocessed photons at energies above 100 MeV and new Galactic interstellar emission models based on CO, H I, dark gas, and interstellar radiation field data. Two different assumptions are used to describe the cosmic-ray distribution in the Galaxy to analyse the systematic uncertainties in source detection and characterization.

The authors applied a 2-dimensional maximum-likelihood detection method similar to that used to analyze the 3rd EGRET catalogue (3EG: Hartman et al. 1999, ApJS, 123, 79, available as the EGRET3 Catalog in Browse).

The revised EGRET catalog (EGR) lists 188 sources, 14 of which are marked as confused, in contrast to the 271 entries of the 3rd EGRET (3EG) catalog. The authors do not detect 107 sources discovered previously because additional structure is present in the interstellar background. The vast majority of them were unidentified and marked as possibly extended or confused in the 3EG catalog. In particular, the authors do not confirm most of the 3EG sources associated with the local clouds of the Gould Belt. Alternatively, they have found 30 new sources that have no 3EG counterpart. The new error circles for the confirmed 3EG sources largely overlap the previous ones, but several counterparts of particular interest discussed before, such as Sgr A*, radio galaxies, and several microquasars are now found outside the error circles. The authors cross-correlated the source positions with a large number of radio pulsars, pulsar wind nebulae, supernova remnants, OB associations, blazars and flat radiosources and they found a surprising large number of sources (87) at all latitudes that have no counterpart among the potential gamma-ray emitters.

Sources found within a radius of 1.5 PSF FWHM of a very bright source, and/or with very asymmetric TS map contours, are not included in the primary list of EGR sources but are included as EGRc sources herein. The EGRc sources represent significant excesses of photons above the background that may be due to extended sources, or structures not properly modeled in the interstellar emission, or artefacts due to incorrect PSF tails.

As noted above, there are 188 sources in this catalog: since there are multiple measurements for these sources corresponding to the various viewing periods, there are 1640 entries in the HEASARC's version of the Revised EGRET Catalog, corresponding to 1512 'observations' of the 174 primary gamma-ray sources plus 128 'observations' of the 14 confused sources. Thus, there are an average of about 9 entries for every gamma-ray source.


Catalog Bibcode

2008A&A...489..849C

References

A Revised Catalogue of EGRET Gamma-ray Sources
    Casandjian J.-M., Grenier I.A.
   <Astronomy and Astrophysics, Volume 489, Issue 2, 2008, pp.849-883>
   =2008A&A...489..849C

Provenance

This table was created by the HEASARC in March 2009 based on the electronic versions of Tables A1 and B1 from the paper, which were obtained from the CDS, their catalog J/A+A/489/849 files egr.dat and egrc.dat.

Parameters

Source_Number
A sequential identification number for each source in the EGR Catalog in order of increasing J2000.0 Right Ascension.

Name
The EGR Catalog source name, using the 'EGR' prefix (for EGret, Revised) for the 174 unconfused sources and the 'EGRc' prefix (for EGret, Revised confused) for the 14 uconfused sources, together with the truncated J2000.0 equatorial source coordinates, e.g., EGR JHHMM+DDMM or EGRc JHHMM+DDMM.

RA
The Right Ascension of the gamma-ray point source in the selected equinox. This was given in J2000.0 decimal degrees to a precision of 0.01 degrees (0.6 arcminutes) in the original table. The source characteristics (position and flux, and their uncertainties) were determined with the Ring model, because of its higher flexibility, better fit, and flatter residual map.

Dec
The Declination of the gamma-ray point source in the selected equinox. This was given in J2000.0 decimal degrees to a precision of 0.01 degrees (0.6 arcminutes) in the original table. The source characteristics (position and flux, and their uncertainties) were determined with the Ring model, because of its higher flexibility, better fit, and flatter residual map.

LII
The Galactic Longitude of the gamma-ray point source.

BII
The Galactic Latitude of the gamma-ray point source.

Error_Radius
The angular radius, in degrees, of a circular cone that contains the same solid angle as the 95% confidence contour. The source characteristics (position and flux, and their uncertainties) were determined with the Ring model, because of its higher flexibility, better fit, and flatter residual map.

Flux
The gamma-ray point source flux for photon energy E > 100 MeV and for the specified time period, in 10-8 ph/cm2/s. The source characteristics (position and flux, and their uncertainties) were determined with the Ring model, because of its higher flexibility, better fit, and flatter residual map.

Flux_Error
The 1-sigma uncertainty in the gamma-ray point source flux for photon energy E > 100 MeV and for the specified time period, in 10-8 ph/cm2/s. The source characteristics (position and flux, and their uncertainties) were determined with the Ring model, because of its higher flexibility, better fit, and flatter residual map.

Counts
The number of photons detected with E > 100 MeV in the specified time period.

Sqrt_TS
The statistical significance (TS)0.5 of the E > 100 MeV detection. It is approximately equal to the number of statistical sigma for a single measurement at a fixed position. See Section 3 of the reference paper for more details. This test statistic used for source detection behaves asymptotically as a chi2 one. The same detection threshold was adopted as for the 3EG Catalog, i.e., (TS)0.5 > 5 at low latitude (|b| < 10 deg), and (TS)0.5 > 4 otherwise.

Viewing_Period
The short viewing period as defined in Table 1 of the reference paper, or summed cycles denoted 'pi' for cycle i, 'pijkl' for the sum of cycles i, j, k, and l, and 'p19' for the sum of all cycles 1-9.

LII_Galprop
The Galactic Longitude of the gamma-ray point source as obtained with the Galprop background model rather than the Ring model. The secondary source positions and fluxes obtained using the Galprop model are given so as to illustrate the amplitude of the systematic uncertainties due to the choice of the interstellar model.

BII_Galprop
The Galactic Latitude of the gamma-ray point source as obtained with the Galprop background model rather than the Ring model. The secondary source positions and fluxes obtained using the Galprop model are given so as to illustrate the amplitude of the systematic uncertainties due to the choice of the interstellar model.

Bck_Flux_Galprop
The gamma-ray point source flux for photon energy E > 100 MeV and for the specified time period, in 10-8 ph/cm2/s.lux, as obtained with the Galprop background model rather than the Ring model. The secondary source positions and fluxes obtained using the Galprop model are given so as to illustrate the amplitude of the systematic uncertainties due to the choice of the interstellar model.

Alt_Name
The Third Egret Catalog (3EG) counterpart source name if one exists within a radius of 1 PSF FWHM (2 degrees for E > 100 MeV) from the EGR source and if the nearest neighbour relation between the EGR and 3EG sources is unequivocal (the nearest neighbour of the EGR source is the 3EG one and vice versa).

EGR_Name
For EGRc sources, this parameter contains the EGR designation, if there is one.


Contact Person

Questions regarding the EGRCAT database table can be addressed to the HEASARC User Hotline.

Page Author: Browse Software Development Team
Last Modified: 9-Mar-2009