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FERMILAC - Fermi LAT Second AGN Catalog



This is the second catalog of active galactic nuclei (AGN) detected by the Fermi Large Area Telescope (LAT) in two years of scientific operation (Ackermann et al. 2011, ApJ 743, 171). The second LAT AGN catalog includes 1017 gamma-ray sources located at high Galactic latitudes (|b| > 10 degrees) that are detected with a test statistic (TS) greater than 25 (approximately 5-sigma) and associated statistically with AGNs. However, some of these are affected by analysis issues and some are associated with multiple AGNs. Consequently, we define a clean sample which includes 886 AGNs, comprising 395 BL Lacertae objects (BL Lac objects), 310 flat-spectrum radio quasars (FSRQs), 157 candidate blazars of unknown type (i.e., with broadband blazar characteristics but with no optical spectral measurement yet), 8 misaligned AGNs, 4 narrow-line Seyfert 1 (NLS1s), 10 AGNs of other types, and 2 starburst galaxies. Where possible, the blazars have been further classified based on their spectral energy distributions (SEDs) as archival radio, optical, and X-ray data permit. This second AGN catalog represents a significant improvement relative to the first LAT AGN catalog, with 52% more associated sources.

Catalog Bibcode



The FERMILAC database table was last updated on 15 May 2012.


A full description of the Second Fermi LAT AGN Catalog is given in "The Second Catalog of Active Galactic Nuclei Detected by the Fermi Large Area Telescope" (Ackermann et al. 2011 ApJ, 743, 171).


This database table was created by the HEASARC in February 2010 based on the electronic data provided by the Fermi Science Support Center (FSSC) representing a combination of Tables 1, 2, and 3 of the referenced paper (Abdo et al. 2010) for the First LAT AGN Catalog.

It was updated in May 2012 to contain the Second LAT AGN Catalog, representing a combination of Tables 3, 4, 7, and 8 of the Ackermann et al. 2011 paper. Data were obtained from the 2LAC database hosted by the Agenzia Spazial Italiano Science Data Center (ASDC) at


The source designation, 2FGL JHHMM.m+DDMM, 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 '2' refers to the second catalog and 'FGL' represents Fermi Gamma-ray LAT.

The designation of the associated AGN, as taken from one of the following astronomical catalogs:

     CRATES  Combined Radio All-sky Targeted Eight GHz Survey (Healey et al. 2007)
     CGRaBS  Candidate Gamma-Ray Blazar Survey (Healey et al. 2008)
     BZn     Roma-BZCAT (Massaro et al. 2009)
     NGC     New General Catalog (Dreyer 1887)
     PKS     Parkes Radio Sources Catalogue (Wright A.E. and Otrupcek R. 1990)
     RX      ROSAT (Bade et al. 1992)
     CLASS   Cosmic Lens All-Sky Survey (Myers et al. 2003; Browne et al. 2003)
     FRBA    Sources observed at 8.4 GHz as part of VLA program AH996
     1WGA    Catalog of ROSAT PSPC Sources (White, Giommi and Angelini 1995)
     4C      4th Cambridge Survey (Pilkington and Scott P F 1965; Gower, Scott
                  and Wills 1967)
     CXOMP   ChandraX-ray Observatory Multiwavelength Project (Kim et al. 2004)
     M       Messier (1782)
     B2,3    Second, Third Bologna Survey (Colla et al. 1970; Ficarra et al. 1985)
     Oa      Ohio Survey (Scheer & Kraus 1967; Rinsland et al. 1975)
     Ton     Tonanzintla Observatory Survey (Chavira 1958)
     1ES     Einstein Slew Survey (Elvis et al. 1992)
     TX      Texas Survey (Douglas et al. 1996)
     Mkn     Markarian (1967)
     SDSS    Sloan Digital Sky Survey
     CXOCY   Chandra X-ray Observatory, Calan Yale (Castander et al., 2003)
     ESO     European Southern Observatory (Lauberts and Valentijn 1989)
     2E      Second Einstein IPC Survey
     PG      Palomar Observatory Green Survey (Green et al., 1986)

The Right Ascension of the associated AGN.

The Declination of the associated AGN.

The Galactic Longitude of the associated AGN.

the Galactic Latitude of the associated AGN.

The angular separation, in degrees, between the 2FGL source position and the position of the associated AGN.

The error in the source position, in degrees, calculated from the geometric mean of the semi-major and semi-minor axes of the gamma-ray 95%-confidence region.

The optical classification of the AGN, as follows:

     AGN             = Active galactic nucleus
     AGU             = Active galaxy of uncertain type
     BL Lac          = BL Lacertae object
     FSRQ            = Flat-spectrum radio quasar
     Radio Galaxy    = Active galaxy that is very luminous at radio wavelengths
     SSRQ            = Steep-spectrum radio quasar
     Starbust Galaxy = Galaxy with an exceptionally high rate of star formation
     Unindentified   = No classification determined

The classification of the AGN spectral energy distribution, based on the synchrotron peak frequency, as follows:

     LSP = low-synchrotron-peaked (sources with peak frequency < 1014 Hz)
     ISP = intermediate-synchrotron-peaked (1014 Hz < peak frequency < 1015 Hz)
     HSP = high-synchrotron-peaked (sources with peak frequency > 1015 Hz)

The redshift of the AGN.

The Bayesian probability of the source association.

The reliability of the likelihood ratio for radio/gamma association.

The reliability of the likelihood ratio for X-ray/gamma association.

The log(N)-log(S) probability of the source association.

The likelihood ratio for radio/gamma association.

The likelihood ratio for X-ray/gamma association.

The photon flux, in units of photons/cm2/s in the 1-100 GeV band.

The 1-sigma uncertainty for the photon flux, in units of photons/cm2/s, in the 1-100 GeV band.

The photon number spectral index.

The 1-sigma uncertainty for the photon spectral index.

The test statistic for detection. This is approximately equal to sigma2.

The radio flux desnsity, in mJy. These are obtained mainly from the GB6 (Gregory et al. 1996) and PMN catalogs and are at 4.85 GHz (6 cm).

This is the X-ray flux, in erg s-1 cm-2. The X-ray fluxes are derived from the ROSAT All Sky Survey (RASS) (Voges et al. 1999), Swift X-Ray Telescope, White-Giommi-Angelini (White et al. 2000), XMM (XMM-Newton Survey Science Centre 2010), and Brera Multi-scale Wavelet (Lazzati et al. 2001) catalogs. RAS, White-Giommi-Angelini & the Brera Multi-Scale wavelet catalogs are in the 0.2-2.4 keV band; XMM & Swift are in the 0.5-12 keV band (approximately).

The V magnitude from the USNO-B1 catalog.

The V magnitude from the SDSS.

The multi-frequency spectral index between the radio and optical bands.

The multi-frequency spectral index between the optical and X-ray bands.

The flag 'Y' indicates that the source is in the clean sample; 'N' otherwise.

The flag 'Y' indicates that the source is in the 2FGL catalog; 'N' otherwise.

Contact Person

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

Page Author: Browse Software Development Team
Last Modified: 15-May-2012