[vsnet-grb-info 13136] GRB 130427A: Fermi GBM observation

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  14473
SUBJECT: GRB 130427A: Fermi GBM observation
DATE:    13/04/27 20:27:19 GMT
FROM:    Andreas von Kienlin at MPE  <azk at 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"