FERMILTRNS - Fermi LAT Long-Term Transient Source Catalog

Overview

The First Catalog of Long-Term Transient Sources detected by Fermi Large Area Telescope (LAT) comprises of 142 unique, transient sources that were detected on monthly time intervals during Fermi-LAT operations. The monthly time scale allows to identify transient and variable sources that were not yet reported in other Fermi-LAT catalogs. The monthly datasets were analyzed using a wavelet-based source detection algorithm that provided the candidate new transient sources. The search was limited to the extragalactic regions of the sky to avoid the dominance of the Galactic diffuse emission at low Galactic latitudes. The transient candidates were then analyzed using the standard Fermi-LAT maximum likelihood analysis method. All sources detected with a statistical significance above 4 sigma in at least one monthly bin were listed in the final catalog.

Catalog Bibcode

2021ApJS..256...13B

References

Baldini et al. (2021), "Catalog of Long-term Transient Sources in the First
       10 yr of Fermi-LAT Data", <ApJS, 256, 13B (2021)>
      =2021ApJS..256...13B

Provenance

This database table was ingested by the HEASARC in September 2021 and is based upon file downloaded from the Space Science Data Center (SSDC) Fermi-1FLT website.

Parameters

Source_Number
Unique, sequential identification number per source in catalog. This is the same for multiple flares of the same source.

Name
The IAU-style J2000 position-based source designation, e.g., '1FLT JHHMM+DDMM'.

RA
The Right Ascension of the source in the selected equinox. This was given in J2000 decimal degree coordinates to an accuracy of 10^-3 degrees (3.6 arcseconds) in the original reference.

Dec
The Declination of the source in the selected equinox. This was given in J2000 decimal degree coordinates to an accuracy of 10^-3 degrees (3.6 arcseconds) in the original reference.

LII
The Galactic longitude of the source.

BII
The Galactic latitude of the source.

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

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

Position_Angle
The position angle of the error ellipse at 95% confidence and defined as degrees east of north.

Likelihood
The likelihood test statistic based on maximum likelihood analysis and defined as 2*Delta(log L), where L is the likelihood function, for the 100 MeV - 300 GeV analysis. This test statistic quantifies how significantly a source emerges from the background by comparing L with and without a source (see Section 2 of the reference paper).

Time_Bin
The time bin in which the source was detected with the largest likelihood test statistic. These time bins correspond to one month (2630000 seconds) that split the total data coverage between 2008 August 4 15:43:36 UTC to 2018 August 5 10:23:32 UTC, e.g., 0-119 stand for the first 120 months starting August 4, 2008, 0.5-119.5 stands for 120 15-day shifted months starting August 19, 2008.

Num_Flares
The number of flares for this source.

Pred_Number
The number of predicted events in the model, which aims to calculate a false positive rate by simulating 120 month-long data sets including Galactic and extragalactic diffuse emission with statistical fluctuations of the background.

PLaw_Photon_Index
The photon index, Gamma, for the power law fit of the spectrum, defined as dN/dE = K * (E/1 GeV)^-Gamma, where K gives the scale flux normalization.

PLaw_Photon_Index_Error
The 1-sigma uncertainty in the photon index for the power law fit of the spectrum.

Photon_Flux
The photon flux, in units of photons/cm²/s, determined from the fit to the power law spectrum. In the original catalog data file, these values had five significant digits in the mantissa. With the authors' approval, the HEASARC displays only two significant digits as appropriate to the number of significant digits in the associated uncertainty.

Photon_Flux_Error
The 1-sigma uncertainty in the photon flux, in photons/cm²/s. In the original catalog data file, these values had five significant digits in the mantissa. With the authors' approval, the HEASARC displays only two significant digits.

Flux
The energy flux, in erg/s/cm², for the 100-MeV to 300-GeV range obtained by spectral fitting in this energy range. In the original catalog data file, these values had five significant digits in the mantissa. With the authors' approval, the HEASARC displays only two significant digits as appropriate to the number of significant digits in the associated uncertainty. The HEASARC also converted these values from MeV/s/cm² to erg/s/cm².

Flux_Error
The 1-sigma uncertainty in the 100-MeV to 300-GeV energy flux, in erg/cm²/s. In the original catalog data file, these values had five significant digits in the mantissa. With the authors' approval, the HEASARC displays only two significant digits. The HEASARC also converted these values from MeV/s/cm² to erg/s/cm².

Fermi_Name
The source name associated with the general Fermi-LAT xFGL (e.g., 4FGL-DR2) or FL8Y catalogs.

Gamma_Name
The source name associated with other gamma-ray source catalogs (see Section 3.2 of reference paper for details).

Fava_Name
The source name associated with 2FAV source catalog (Abdollahi et al, 2017).

LMC_Flag
Flag 'Y' indicates that the source is located in the Large Magellanic Cloud (LMC) region. Otherwise, the value is 'N'.

Cena_Flag
Flag 'Y' Indicates that the source is located near Cen A. Otherwise, the value is 'N'.

Source_Type
The class designation of the associated source, which is described in Section 3.1 of the reference paper, and marked to represent the following:

  	fsrq   = Flat spectrum Radio Quasar
  	bll    = BL Lacertae object
  	css    = Compact Steep Spectrum radio source
  	ssrq   = Steep Spectrum Radio Quasar
  	rg     = Radio Galaxy
  	bcu    = Blazars of Uncertain Type
  	agn    = Active Galactic Nuclei of other type
  	unass  = unassociated

Assoc_Name
The designation of the most likely associated counterpart.

Assoc_Prob_Bay
Probability of association from the Bayesian method.

Assoc_RA
The Right Ascension of the associated source.

Assoc_Dec
The Declination of the associated source.

Assoc_Redshift
The redshift of the associated source.

Flux_1420_MHz
The radio flux density, in mJy, for the source.

Log_Freq_Peak
The logarithm (base 10) of the synchrotron peak frequency, in Hz, measured with a third degree polynomial fit function to the broadband SED (following Ackermann et al. 2015, see Section 4.2 of reference paper).

Low_Confidence_Flag
Flag 'Y' indicates that the source has low confidence, due to test statistic (likelihood parameter) value < 30 and only one monthly detection.

Class
The HEASARC Browse object classification, based on the source_type parameter.

Contact Person

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

Page Author: Browse Software Development Team
Last Modified: Wednesday, 29-Sep-2021 15:24:33 EDT