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FERMILPSC - Fermi LAT 8-Year Point Source Catalog

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Overview

The Fermi LAT 8-Year Point Source Catalog (4FGL) is a catalog of high-energy gamma-ray sources detected by the Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope (Fermi) mission during the first eight years of science data.

Relative to the 3FGL (4-year) catalog, the 4FGL catalog has twice as much exposure as well as a number of analysis improvements, including an updated model for Galactic diffuse gamma-ray emission. The 4FGL catalog includes 5065 sources above 4 sigma significance, for which we provide localization and spectral properties. Seventy-five sources are modeled explicitly as spatially extended, and overall 355 sources are considered as identified based on angular extent or correlated variability observed at other wavelengths. For 1323 sources we have not found plausible counterparts at other wavelengths. More than 3130 of the identified or associated sources are active galaxies of the blazar class, 239 are pulsars.


Catalog Bibcode

2019arXiv190210045T

Bulletin

The FERMILPSC database table was last updated on 29 May 2019.

Caveats

We emphasize several important points and caveats regarding use of the 4FGL catalog:


References

A full description of the LAT 8-Year Point Source Catalog is given in the "Fermi Large Area Telescope Fourth Source Catalog" by the Fermi LAT team. Additional information for which is available at http://fermi.gsfc.nasa.gov/ssc/data/access/lat/8yr_catalog/.

Provenance

This database table was updated by the HEASARC in May 2019 using electronic data obtained from the Fermi Science Support Center (FSSC) available at http://fermi.gsfc.nasa.gov/ssc/data/access/lat/8yr_catalog/.

Parameters

Name
The source designation, 4FGL JHHMM.m+DDMM[c], constructed according to the IAU Specifications for Nomenclature, in which the Right Ascension and Declination have been truncated to 0.1 decimal minutes and 1', respectively. The '4' refers to the eight-year catalog (the first-year catalog was '1'; the second-year catalog was '2'; the four-year catalog was '3') and 'FGL' represents Fermi Gamma-ray LAT. The letter at the end can be "c" (coincident with interstellar clump), "e" (extended source), "i" (for Crab nebula inverse Compton) or "s" (for Crab nebula synchrotron).

RA
The Right Ascension of the gamma-ray source in the selected equinox. This was given in J2000 decimal degree coordinates in the original table.

Dec
The Declination of the gamma-ray source in the selected equinox. This was given in J2000 decimal degree coordinates in the original table.

LII
The Galactic Longitude of the gamma-ray source, as derived from the J2000 position in the original table.

BII
The Galactic Latitude of the gamma-ray source, as derived from the J2000 position in the original table.

Semi_Major_Axis_68
The semi-major axis of the error ellipse at 68% confidence, in degrees.

Semi_Minor_Axis_68
The semi-minor axis of the error ellipse at 68% confidence, in degrees.

Position_Angle_68
The position angle of the 68%-confidence semi-major axis, from celestial North, positive toward increasing R.A. (eastward), in degrees.

Semi_Major_Axis_95
The semi-major axis of the error ellipse at 95% confidence, in degrees.

Semi_Minor_Axis_95
The semi-minor axis of the error ellipse at 95% confidence, in degrees.

Position_Angle_95
The position angle of the 95%-confidence semi-major axis, from celestial North, positive toward increasing R.A. (eastward), in degrees.

Detection_Significance
The source detection significance, in Gaussian sigma units, over the 100 MeV to 1 TeV band.

Pivot_Energy
The energy, in MeV, at which the error in the differential photon flux is minimal (i.e., the decorrelation energy for the power-law fit). This is derived from the likelihood analysis for 100 MeV - 1 TeV.

Flux_1_100_GeV
The integral photon flux for 1 - 100 GeV, in photons/cm2/s.

Flux_1_100_GeV_Error
The 1-sigma uncertainty in the integral photon flux for 1 - 100 GeV, in photons/cm2/s.

Energy_Flux
The energy flux, in erg/cm2/s, in the 100 MeV to 100 GeV range obtained by spectral fitting from 100 MeV to 100 GeV.

Energy_Flux_Error
The 1-sigma error on energy flux from 100 MeV to 100 GeV.

Spectrum_Type
The spectral type in the global model (PowerLaw, LogParabola, PLSuperExpCutoff).

PL_Flux_Density
The differential flux at pivot_energy for the PowerLaw fit, in photons/cm2/MeV/s.

PL_Flux_Density_Error
The 1-sigma uncertainty in differential flux at pivot_energy in PowerLaw fit, in photons/cm2/MeV/s.

PL_Index
The photon index for the PowerLaw fit.

PL_Index_Error
The 1-sigma uncertainty on the photon index for PowerLaw fit.

LP_Flux_Density
The differential flux at pivot_energy for the LogParabola fit, in photons/cm2/MeV/s.

LP_Flux_Density_Error
The 1-sigma uncertainty in differential flux at pivot_energy in LogParabola fit, in photons/cm2/MeV/s. lp_index The 1-sigma uncertainty on the photon index for LogParabola fit.

LP_Index
Photon Index at Pivot Energy for LogParabola Fit

LP_Index_Error
The 1-sigma uncertainty on the photon index for LogParabola fit.

LP_Beta
The curvature parameter (beta) for LogParabola spectrum types.

LP_Beta_Error
The 1-sigma uncertainty on lp_beta for LogParabola spectrum types.

LP_Curve_Significance
The significance in sigma of the fit improvement between PowerLaw and LogParabola fits.

PLEC_Flux_Density
The differential flux at pivot_energy for the PLSuperExpCutoff fit, in photons/cm2/MeV/s.

PLEC_Flux_Density_Error
The 1-sigma uncertainty in differential flux at pivot_energy in PLSuperExpCutoff fit, in photons/cm2/MeV/s.

PLEC_Index
The low energy photon index for PLSuperExpCutoff fit.

PLEC_Index_Error
The 1-sigma uncertainty on plec_index for PLSuperExpCutoff fit.

PLEC_Exp_Factor
The exponential factor for PLSuperExpCutoff fit.

PLEC_Exp_Factor_Error
The 1-sigma uncertainty on exponential factor for PLSuperExpCutoff fit.

PLEC_Exp_Index
The exponential index for PLSuperExpCutoff fit.

PLEC_Exp_Index_Error
The 1-sigma uncertainty on exponential index for PLSuperExpCutoff fit.

PLEC_Curve_Significance
The significance in sigma of the fit improvement between PowerLaw and PLEC fits.

Npred
The number of predicted events in the model.

Variability_Index
The sum of the log(likelihood) difference between the flux fitted in each time interval and the average flux over the full catalog interval; a value greater than 18.48 over 12 intervals indicates <1% chance of being a steady source. See the accompanying paper for details.

Frac_Variability
The fractional variability computed from the fluxes in each year.

Frac_Variability_Error
The 1-sigma uncertainty on exponential index on the fractional variability.

Significance_Peak
The source significance in peak interval in sigma units.

Flux_Peak
The peak integral photon flux from 100 MeV to 100 GeV, in photon/cm2/s.

Flux_Peak_Error
The 1-sigma error on peak integral photon flux, in photon/cm2/s

Time_Peak
Time of center of interval in which peak flux was measured, in MJD.

Time_Peak_Interval
Length of interval in which peak flux was measured, in seconds.

Alt_GammaRay_Name_1
Most recent correspondence to previous FGL source catalogs, if any.

Alt_GammaRay_Name_2
Most recent correspondence to previous FHL source catalogs, if any.

Alt_GammaRay_Name_3
Name of likely corresponding 2AGL source, if any.

Alt_GammaRay_Name_4
Name of likely corresponding 3EG source, if any.

Alt_GammaRay_Name_5
Name of likely corresponding EGR source, if any.

Extended_Source_Name
The extended source identification, if any.

TeVCat_Flag
This flag parameter indicates a possible association with the TeVCat. The flag values have the following meanings:

             N = No TeV association
             P = Small TeV source
             E = Extended TeV source (diameter > 40 arcminutes)
  

TeVCat_Assoc
The designation of the likely corresponding source from the TeVCat catalog, if any.

Source_Type
The primary class designation of the identification or likely associated source. Refer to the accompanying paper for details of class designations and the association method. Note that designations shown in capital letters are firm identifications; lower case letters indicate associations. The following abbreviations are used:

            agn   = other non-blazar active galaxy
            bcu   = active galaxy of uncertain type
            bin   = binary
            bll   = BL Lac type of blazar
            css   = compact steep spectrum quasar
            fsrq  = FSRQ type of blazar
            gal   = normal galaxy (or part)
            glc   = globular cluster
            hmb   = high-mass binary
            mc    = molecular cloud
            nlsy1 = narrow line Seyfert 1
            nov   = nova
            PSR   = pulsar, identified by pulsations
            psr   = pulsar, no pulsations seen in LAT yet
            pwn   = pulsar wind nebula
            rdg   = radio galaxy
            sbg   = starburst galaxy
            sey   = Seyfert galaxy
            sfr   = star-forming region
            snr   = supernova remnant
            spp   = special case - potential association with SNR or PWN
            ssrq  = soft spectrum radio quasar
            unk   = unknown
  

Source_Type_Alt
Class designation for an alternative, low-confidence association.

Assoc_Name
The designation of the identified or likely associated source.

Assoc_Name_Alt
The alternate designation or an indicator as to whether the source is inside an extended source.

Assoc_Prob_Bay
The probability of association according to the Bayesian method. It is set to NULL for extended sources (which do not enter that calculation) and to 0 for point sources that did not reach 0.8, the threshold for declaring associations.

Assoc_Prob_LR
The probability of association according to the Likelihood Ratio method. It is set to NULL for extended sources (which do not enter that calculation) and to 0 for point sources that did not reach 0.8, the threshold for declaring associations.

Assoc_RA
The Right Ascension of assoc_name counterpart, in degrees.

Assoc_Dec
The Declination of assoc_name counterpart, in degrees.

Assoc_Error_Radius
The position uncertainy at 68% confidence level of the counterpart localization for assoc_name, in degrees.

Analysis_Flags
These analysis flags indicate possible issues noted in the detection or characterization of the source. A value of 0 indicates no known problem. Each condition present raises a unique bit flag. The flag values are bit-encoded into a single integer, with flag N contributing 2N-1 to the value, where N is given as:

      N=1: Source with TS > 35 which went to TS < 25 when changing the diffuse
           model. Note that sources with TS < 35 are not flagged with this bit
           because normal statistical fluctuations can push them to TS < 25.

      N=2: Not used.

      N=3: Flux (> 1 GeV) or energy flux (> 100 MeV) changed by more than 3
           sigma when changing the diffuse model or the analysis method. Requires
           also that the flux change by more than 35% (to not flag strong
           sources).

      N=4: Not used.

      N=5: Not used.

      N=6: Not used.

      N=7: Not used.

      N=8: Not used.

      N=9: Localization Quality > 8 in pointlike (see Section 3.1 in catalog
           paper) or long axis of 95% ellipse > 0.25.

      N=10: Spectral Fit Quality > 30 in pointlike.

      N=11: Not used.

      N=12: Highly curved spectrum; LogParabola beta fixed to 1 or PLEC_Index
            fixed to 0 (see Section 3.3 in catalog paper).
  

Contact Person

Questions regarding the FERMILPSC database table can be addressed to the HEASARC User Hotline.
Page Author: Browse Software Development Team
Last Modified: Thursday, 06-Jun-2019 20:10:56 EDT