GCN Circular 14473
Subject
GRB 130427A: Fermi GBM observation
Event
Date
2013-04-27T20:27:19Z (12 years ago)
From
Andreas von Kienlin at MPE <azk@mpe.mpg.de>
A. von Kienlin (MPE) reports on behalf of the Fermi GBM Team:
"At 07:47:06.42 UT on 27 April 2013, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 130427A (trigger 388741629/130427324) which
was also detected by the Swift/BAT and Fermi/LAT (Maselli et al. 2013,
GCN 14448 and S. Zhu et al., GCN 14471) The GBM on-ground location is
consistent with the Swift position.
The angle from the Fermi LAT boresight is 48 degrees.
Based on hard and intense emission in a GBM BGO detector, GBM
initiated an Autonomous Report Request. This request caused Fermi
to reorient towards this GRB (GBM flight location).
The GBM light curve consists of a bright structured peak followed
at ~T0+120 s by a FRED-like pulse. The overall duration (T90)
is about 138s s (50-300 keV).
Owing to the brightness of the burst, systematic effects are very large
and no single model gives an adequate fit in this preliminary analysis.
A Band function fit in the interval from T0+0.002 s to T0+18.432 s yields
the following parameters Epeak = 830 +/- 5 keV, alpha = -0.789 +/- 0.003,
and beta = -3.06 +/- 0.02.
The event fluence (10-1000 keV) in this time interval is
(1.975 +/- 0.003)E-03 erg/cm^2. The 1.024 sec peak photon flux measured
starting from T0+7.48808 s in the 8-1000 keV band
is 1052 +/- 2 ph/s/cm^2, making this the most intense and fluent GRB
detected by Fermi GBM.
Further analysis is being performed"