[vsnet-grb-info 7757] GRB 090429D: Fermi GBM detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  9311
SUBJECT: GRB 090429D: Fermi GBM detection
DATE:    09/04/30 22:09:24 GMT
FROM:    Narayana Bhat at U Alabama/Huntsville/GBM  <Narayana.Bhat at nasa.gov>

P. N. Bhat (UAH) reports on behalf of the Fermi GBM Team:

"At 18:03:57.51 UT on 29 April 2009, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 090429D (trigger 262721039 / 090429753).

The on-ground calculated location, using the GBM trigger
data, is RA = 125.2, DEC = 6.2 (J2000 degrees,
equivalent to 08 h 20.8 m, 06 d 12'), with an uncertainty
of 4.6 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 33 degrees.

[This burst was also independently detected by Konus Wind. Swift BAT
confirms this GRB which occurred while it was slewing.]


The GBM light curve consists of 3 short pulses (two which occurred before
the trigger) with a duration (T90) of about 11 s (8-1000 keV).
The time-averaged spectrum from T0-13.248 s to T0+1.088 s is
adequately fit by a power law function with an exponential
high energy cutoff.  The power law index is -0.87 +/- 0.27 and
the cutoff energy, parametrized as Epeak, is 223 +/- 72.5 keV
(chi squared 459 for 487 d.o.f.).

The event fluence (8-1000 keV) in this time interval is
(1.6 +/- 0.3)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0 s in the 8-1000 keV band
is 0.86 +/- 0.16 ph/s/cm^2.

[A Band function fits the spectrum equally well (chi squared 456 for 486
d.o.f.) with Epeak= 152.8 +/- 92.4 keV, alpha = -0.66 +/- 0.53 and beta =
-1.88+/- 0.32.] 

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