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FERMIGTRIG - Fermi GBM Trigger Catalog |
HEASARC Archive |
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. These 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. To cover higher energies, the GBM also includes two bismuth germanate (BGO) detectors.
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.
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
This parameter contains 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 table.
Dec
The Declination of the X-ray source in the selected equinox. This was given in J2000 decimal degree coordinates in the original table.
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.
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 types
are given in the Fermi File Format Document for this file (GS-105):
ERROR Error UNRELOC Unreliable location LOCLPAR Local particles BELOWHZ Source below the horizon GRB Gamma-ray burst SGR Generic soft gamma repeater TRANSNT Generic transient DISTPAR Distance particle event SFL Solar flare CYGX1 Variation of Cyg X-1 SGR1806 Burst from SGR1806+20 GROJ422 Variation of GRO J0422+32 TGF Terrestrial Gamma-Ray Flash
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 algorthims.
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 (0-11) were triggered. The value 1 at a particular position
indicates that that detector was triggered. Similarly, the value 0 indicates
that that dectector 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.