[vsnet-grb-info 8386] GRB 090910: Fermi GBM detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  9904
SUBJECT: GRB 090910: Fermi GBM detection
DATE:    09/09/11 19:32:46 GMT
FROM:    Vandiver Chaplin at UAH/Fermi-GBM  <chapliv at email.uah.edu>

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

"At 19:29:48.81 UT on 10 SEP 2009, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 090910 (trigger 274303790 / 090910812).

The on-ground calculated location, using the GBM trigger
data, is RA = 296.2, DEC = 72.3 (J2000 degrees,
equivalent to 19h 44m, 72 d 18'), 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 107 degrees.

The on-board GBM Flight Software localization for this event,
as reported in the GCN notice, was consistent with a position
near the Earth's limb.  Furthermore, the trigger occurred as
the spacecraft was at a high magnetic latitude.  The resulting
autonomous classification for the event was "Distant Particles",
which is erroneous.

The GBM light curve consists of three distinct pulses
close in time from T0-5s to about T0+45s, with a smaller pulse
visible in several detectors at about T0+70s.  The duration (T90)
of this event is approximately 62s (8-1000 keV).
The time-averaged spectrum from T0-7.2 s to T0+44 s is
best fit by a Band function with Epeak = 274.8 +/- 56.1 keV,
alpha = -0.9 +/- 0.1, and beta = -2.0 +/- 0.2 (chi squared 397.41
for 360 d.o.f.).

The event fluence (8-1000 keV) in this time interval is
(9.2 +/- 0.7)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+2 s in the 8-1000 keV band
is 2.3 +/- 0.6 ph/s/cm^2.

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