FERMIGTRIG - Fermi GBM Trigger Catalog
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.
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).
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.
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.
The Right Ascension of the trigger in the selected equinox. This was given in J2000 decimal degree coordinates in the original data.
The Declination of the trigger in the selected equinox. This was given in J2000 decimal degree coordinates in the original data.
The Galactic Longitude of the trigger, derived from the trigger RA and Dec.
The Galactic Latitude of the trigger, derived from the trigger RA and Dec.
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.
The start time of the observation, originally provided in Fermi Mission Elapsed Time (MET) format and converted to UTC.
The end time of the observation, originally provided in Fermi Mission Elapsed Time (MET) format and converted to UTC.
The time at which the trigger occurred, originally provided in Fermi Mission Elapsed Time (MET) format and converted to UTC.
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
Probability assigned to the classification of the trigger by the GBM flight software, expressed as a percentage (with 100% being most probable).
The timescale (in milliseconds) that actually produced the trigger. GBM has many, from 16 ms up to about 4 s.
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.
The lowest energy channel in which the trigger was detected.
The highest energy channel in which the trigger was detected.
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.
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.
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.
The spacecraft's geographical north latitude, in degrees.
The spacecraft's geographical east longitude, in degrees.
The Right Ascension of the pointing of the spacecraft's X-axis, in J2000 degrees.
The Declination of the pointing of the spacecraft's X-axis, in J2000 degrees.
The Right Ascension of the pointing of the spacecraft's Z-axis, in J2000 degrees.
The Declination of the pointing of the spacecraft's Z-axis, in J2000 degrees.
The angle of best localization to the LAT boresight, range 0 - 180 degrees.
The angle of best localization in azimuth measured from +x axis counterclockwise, to +y axis, range 0 - 360 degrees.
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