FERMIGTRIG - Fermi GBM Trigger Catalog

Overview

This table lists all of the triggers observed by one or more of the 14 GBM detectors (12 NaI and 2 BGO). Note that there are two Browse catalogs resulting from GBM triggers. All GBM triggers are entered in the Trigger Catalog, but only those triggers classified as bursts are entered in the Fermi GBM Burst Catalog. Thus, a burst will be found in both the Trigger and Burst Catalogs. The Burst Catalog analysis requires human intervention; therefore, GRBs will be entered in the Trigger Catalog before the Burst Catalog. The latency requirements are 1 day for triggers and 3 days for bursts.

The GBM consists of an array of 12 sodium iodide (NaI) detectors which cover the lower end of the energy range up to 1 MeV. The GBM triggers off of the rates in the NaI detectors, with some Terrestrial Gamma-ray Flash (TGF)-specific algorithms using the bismuth germanate (BGO) detectors, sensitive to higher energies, up to 40 MeV. The NaI detectors are placed around the Fermi spacecraft with different orientations to provide the required sensitivity and FOV. The cosine-like angular response of the thin NaI detectors is used to localize burst sources by comparing rates from detectors with different viewing angles. The two BGO detectors are placed on opposite sides of the spacecraft so that all sky positions are visible to at least one BGO detector.

The signals from all 14 GBM detectors are collected by a central Data Processing Unit (DPU). This unit digitizes and time-tags the detectors' pulse height signals, packages the resulting data into several different types for transmission to the ground (via the Fermi spacecraft), and performs various data processing tasks such as autonomous burst triggering.

Bulletin

The FERMIGTRIG database table was last updated on 16 November 2024.

Caveats

Please see the warnings on the GBM Caveats page, http://fermi.gsfc.nasa.gov/ssc/data/analysis/GBM_caveats.html.

References

See the Fermi Science Data Product Interface Control Document (http://fermi.gsfc.nasa.gov/ssc/library/support/Science_DP_ICD_RevA.pdf).

Provenance

The information in this table is provided by the Fermi Gamma-ray Burst Monitor Instrument Operations Center (GIOC) and the Fermi Science Support Center (FSSC). The values come from a trigger catalog entry file or a burst catalog entry file provided by the GIOC. These are FITS files which may contain additional data in extensions for bursts (see the spectrum_flag and fit_flag columns) and are available for download. This table is updated automatically within a day or so of new data files being processed and made available.

Parameters

Version
This parameter specifies the current version of the catalog entry file. New versions are provided by the GIOC as additional data are added or further analysis done. Thus the early versions might have only basic burst quantities such as duration in the header, while later versions will have spectra in extensions (which are not provided in earlier versions).

Trigger_Name
The Fermi trigger designation that is assigned for each new trigger detected. The naming scheme used is bnyymmddfff, where yymmdd is the date of the burst (yy, the year minus 2000; mm, the two-digit month; and dd, the two-digit day of the month) and fff = fraction of day.

Name
The designation of the source of the trigger. The name will initially be GRByymmddfff, where yymmdd is the 2-digit year, month and day of the burst and fff the fraction of the day, as assigned by pipeline processing. The name will eventually be changed to the GRByymmddx format, where x is null or 'A' or 'B' etc. Re-naming to this format requires human intervention, noting whether another burst was detected on the same day.

RA
The Right Ascension of the trigger in the selected equinox. This was given in J2000 decimal degree coordinates in the original data.

Dec
The Declination of the trigger in the selected equinox. This was given in J2000 decimal degree coordinates in the original data.

LII
The Galactic Longitude of the trigger, derived from the trigger RA and Dec.

BII
The Galactic Latitude of the trigger, derived from the trigger RA and Dec.

Error_Radius
This parameter is the uncertainty in the position, in degrees. A value of 0 means that the source localization was done using something other than Fermi GBM (for example, Swift, XMM, Chandra, etc.), so that the error radius is negligible by GBM standards. A value of 50 means that the localization is not well determined. As noted in footnote (22) of von Kienlin et al. (2014), this error is the statistical 1-sigma error; the GBM errors are not symmetric, and the given value is the average of the error ellipse.

Time
The start time of the observation, originally provided in Fermi Mission Elapsed Time (MET) format and converted to UTC.

End_Time
The end time of the observation, originally provided in Fermi Mission Elapsed Time (MET) format and converted to UTC.

Trigger_Time
The time at which the trigger occurred, originally provided in Fermi Mission Elapsed Time (MET) format and converted to UTC.

Trigger_Type
The classification of the trigger. The following trigger classes are given in the Fermi File Format Document for this file (GS-105):

  DISTPAR	Distance particle event
  GALBIN	Galactic binary
  GRB	Gamma-ray burst
  LOCLPAR	Local particles
  SFLARE	Solar flare
  SGR	Soft gamma repeater
  TGF	Terrestrial Gamma-Ray Flash
  TRANSNT	Generic transient
  UNCERT	Uncertain classification

Reliability
Probability assigned to the classification of the trigger by the GBM flight software, expressed as a percentage (with 100% being most probable).

Trigger_Timescale
The timescale (in milliseconds) that actually produced the trigger. GBM has many, from 16 ms up to about 4 s.

Trigger_Algorithm
This parameter contains the trigger algorithm number used by the GBM flight software. Currently, there is only one algorithm used which is assigned the number 1. Future versions of the flight software may use other algorithms.

Channel_Low
The lowest energy channel in which the trigger was detected.

Channel_High
The highest energy channel in which the trigger was detected.

ADC_Low
The lowest energy channel, after analog-digital conversion, in which the trigger was detected. Channel values after analog-digital conversion are in the range 0 - 4095.

ADC_High
The highest energy channel, after analog-digital conversion, in which the trigger was detected. Channel values after analog-digital conversion are in the range 0 - 4095.

Detector_Mask
This field contains a series of flags which indicate which NaI detectors (bytes 0-11) and BGO detectors (bytes 12-13, where known) were triggered. The value 1 at a particular position indicates that that detector was triggered. Similarly, the value 0 indicates that that detector was not triggered.

Geo_Long
The spacecraft's geographical north latitude, in degrees.

Geo_LAT
The spacecraft's geographical east longitude, in degrees.

RA_Scx
The Right Ascension of the pointing of the spacecraft's X-axis, in J2000 degrees.

Dec_Scx
The Declination of the pointing of the spacecraft's X-axis, in J2000 degrees.

RA_Scz
The Right Ascension of the pointing of the spacecraft's Z-axis, in J2000 degrees.

Dec_Scz
The Declination of the pointing of the spacecraft's Z-axis, in J2000 degrees.

Theta
The angle of best localization to the LAT boresight, range 0 - 180 degrees.

Phi
The angle of best localization in azimuth measured from +x axis counterclockwise, to +y axis, range 0 - 360 degrees.

Localization_Source
The source of the coordinate localization used for the trigger. Allowed values:

            Fermi, GBM (default)
            Fermi, LAT
            Swift, BAT
            Swift, XRT
            SuperAGILE
            INTEGRAL
            Known Source

Contact Person

Questions regarding the FERMIGTRIG database table can be addressed to the HEASARC Help Desk.

Page Author: Browse Software Development Team
Last Modified: Monday, 16-Sep-2024 17:27:27 EDT