[vsnet-grb-info 7885] GRB 090520D: Fermi GBM detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  9429
SUBJECT: GRB 090520D: Fermi GBM detection
DATE:    09/05/28 13:45:04 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 21:01:37.14 UT on 20 May 2009, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 090520D (trigger 264546099 / 090520876).

The on-ground calculated location, using the GBM trigger
data, is RA = 131.3, DEC = -18.0 (J2000 degrees,
equivalent to 08 h 45.2 m, -18 d 0'), with an uncertainty
of 4.3 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 66 degrees.

The GBM light curve consists of single pulse
with a duration (T90) of about 12 s (8-1000 keV).
The time-averaged spectrum from T0-5.12 s to T0+13.3 s is
adequately fit by

a power law function with an exponential
high energy cutoff.  The power law index is -1.03 +/- 0.22 and
the cutoff energy, parameterized as Epeak, is 47.4 +/- 4.1 keV

(chi squared 354 for 363 d.o.f.).

The event fluence (8-1000 keV) in this time interval is
(4.0 +/- 0.9)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+2.0 s in the 8-1000 keV band
is 4.1 +/- 1.0 ph/s/cm^2.

A Band function fits the spectrum equally well (chi squared 353.8 for 362
d.o.f.) 
with Epeak= 46.3 +/- 5.3 keV, alpha = -0.99 +/- 0.28 and beta = -3.25 +/-
1.23. 


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