[vsnet-grb-info 8167] GRB 090720B: Fermi GBM detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  9698
SUBJECT: GRB 090720B: Fermi GBM detection
DATE:    09/07/22 13:57:40 GMT
FROM:    Michael Burgess at UNH  <james.burgess at uah.edu>

J. M. Burgess (UAH), A. Goldstein (UAH) and A. J. van der Horst
(NASA/MSFC/ORAU) report on behalf of the Fermi GBM Team:

"At 17:02:56.91 UT on 20 July 2009, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 090720B (trigger 269802178 / 090720710).
The on-ground calculated location, using the GBM trigger
data, is RA = 203.0, DEC = -54.8 (J2000 degrees,
equivalent to 13h 32m, -54d 48'), with an uncertainty
of 2.9 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 56 degrees.

This burst was also independently detected by INTEGRAL SPI-ACS.

The GBM light curve consists of two bright peaks with a
duration (T90) of about 20 s (8-1000 keV).
The time-averaged spectrum from T0+0.0 s to T0+20.1 s is well
fit by a power law function with an exponential high energy cutoff.
The power law index is -1.01 +/- 0.05 and the cutoff energy,  
parameterized
as Epeak, is 982 +/- 186 keV (chi squared 484 for 483 d.o.f.).

The event fluence (8-1000 keV) in this time interval is
(1.06 +/- 0.03)E-5 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+5.8 s in the 8-1000 keV band
is 10.9 +/- 0.4 ph/s/cm^2.

A Band function fits the spectrum equally well (chi squared 482 for
482 d.o.f.) with Epeak= 924 +/- 201 keV, alpha = -1.00 +/- 0.05
and beta = -2.43 +/- 0.47.

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