[vsnet-grb-info 8960] GRB 100225A: Fermi GBM detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  10449
SUBJECT: GRB 100225A: Fermi GBM detection
DATE:    10/02/25 15:41:30 GMT
FROM:    Sheila McBreen at MPE  <smcbreen at mpe.mpg.de>

S. Foley (MPE) and S. McBreen (UCD/MPE) report on
behalf of the Fermi GBM Team:

"At 02:45:31.15 UT on 25 February 2010, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 100225A (trigger 288758733 / 100225115).

The on-ground calculated location, using the GBM trigger
data, is RA = 312.5, DEC = -54.9 (J2000 degrees,
equivalent to 20 h 50 m, -54 d 54 '), with an uncertainty
of 2.4 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 58 degrees.

The GBM light curve consists of two main pulses
with a duration (T90) of about 13 (+/-3) s (50-300 keV)
starting at -0.256 s. The time-averaged spectrum
from T0-3.8 s to T0+13.6 s is well fit by
a power law function with an exponential high energy cutoff.
The power law index is -0.80 (+0.09/-0.08) and
the cutoff energy, parameterized as Epeak, is
527.30 (+105.00/-76.10) keV (CSTAT 438 for 361 d.o.f.).

The event fluence (8-1000 keV) in this time interval is
(7.6 +/- 0.3)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+6.4 s in the 8-1000 keV band
is 4.13 +/- 0.20 ph/s/cm^2.

A Band function fits the spectrum equally well (CSTAT 436 for 360 d.o.f.)
with Epeak= 428.00 (+130.00/-86.00) keV, alpha = -0.72 (+0.13/-0.12)
and beta = -2.15 (+0.21/-0.75).


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