[vsnet-grb-info 16106] GRB 150202B: Fermi GBM detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  17388
SUBJECT: GRB 150202B: Fermi GBM detection
DATE:    15/02/03 11:08:57 GMT
FROM:    Hoi-Fung Yu at MPE  <sptfung at mpe.mpg.de>

V. Pelassa (UAH) reports on behalf of the Fermi GBM Team:

"At 23:59:08.27 UT on 02 Feb 2015, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 150202B (trigger 444614351 / 150202999).

The on-ground calculated location, using the GBM trigger data, is
RA = 86.8, Dec = 58.6 (J2000 degrees, equivalent to +05h 47m, +58d 32'),
with an uncertainty of 1.0 degrees (radius, 1-sigma containment,
statistical only; there is additionally a systematic error which is
currently estimated to be 2 to 3 degrees). The angle from the Fermi LAT
boresight is 17 degrees. This trigger resulted in an Autonomous Repoint
Request (ARR) that was accepted and the spacecraft slewed to the GBM
in-flight location. Following this observation the Fermi Large Area 
Telescope also detected this burst in the ground-based analysis 
(Axelsson et al. 2015, GCN 17385).

This GRB was also detected by Integral/SPI-ACS.

The GBM light curve consists of a bright peak lasting about 25 s, 
followed at T0+ 100 s by a fainter second episode of emission, 
with a total duration (T90) of about 167 s (50-300 keV). 
The 1.024-sec peak photon flux measured starting from T0+7.808 s 
in the 10-1000 keV band is 23.8 +/- 0.4 ph/s/cm^2.

The time-averaged spectrum of the first episode, from T0-5.120 s to
T0+24.576 s, is best fit by a Band function with Epeak = 253 +/- 12 keV,
alpha = -0.82 +/- 0.02, and beta = -2.36 +/- 0.13. The event fluence 
(10-1000 keV) in this time interval is (3.15 +/- 0.05)E-05 erg/cm^2.

The time-averaged spectrum of the second episode, from T0+103.426 s to
T0+205.827 s, is well fit a power law function with an exponential
high-energy cutoff. The power law index is -1.23 +/- 0.13 and
the cutoff energy, parameterized as Epeak, is 154 +/- 36 keV. 
The event fluence (10-1000 keV) in this time interval 
is (1.37 +/- 0.15)E-06 erg/cm^2.

The spectral analysis results presented above are preliminary;
final results will be published in the GBM GRB Catalog."