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GCN Circular 29763

Subject
GRB 210402A: Fermi GBM detection
Date
2021-04-05T20:19:05Z (3 years ago)
From
Oliver J Roberts at USRA/NASA <oliver.roberts@nasa.gov>
O.J. Roberts (USRA/MSFC) and C. Meegan (UAH)
report on behalf of the Fermi GBM Team:

"At 22:04:16.98 UT on the 2nd April 2021, the Fermi Gamma-Ray Burst Monitor (GBM)
triggered and located GRB 210402A (trigger 639093861 / 210402920), which was also
detected by the Swift/BAT (Page et al. 2021, GCN 29743). The GBM on-ground 
location is consistent with the Swift position.

The angle from the Fermi LAT boresight at the GBM trigger time is 44 degrees.

The GBM light curve consists of several broad, faint peaks, including emission 
about 60 s prior to the trigger time. The T90 duration of the event is about 
76 s (50-300 keV). The time-averaged spectrum from T0-60 s to T0+16 s is adequately 
fit by a simple power law function with index -1.34 +/- 0.03.

The event fluence (10-1000 keV) in this time interval is
(1.699 +/- 0.008)E-6 erg/cm^2. The 1-sec peak photon flux measured
starting from T0-52.7 s in the 10-1000 keV band is 1.5 +/- 0.2 ph/s/cm^2. 

Due to the powering down of Fermi-GBM detectors because of SAA entry about 19 s 
after the trigger time (note T90), the T90 duration, peak fluxes and fluences 
are lower limits only.

The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog:
https://heasarc.gsfc.nasa.gov/W3Browse/fermi/fermigbrst.html

For Fermi GBM data and info, please visit the official Fermi GBM Support Page:
https://fermi.gsfc.nasa.gov/ssc/data/access/gbm/"
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