[vsnet-grb-info 6841] GRB 081028B: Fermi GBM detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  8433
SUBJECT: GRB 081028B: Fermi GBM detection
DATE:    08/10/28 21:57:03 GMT
FROM:    Elisabetta Bissaldi at MPE  <ebs at mpe.mpg.de>

E. Bissaldi (MPE) and A. von Kienlin (MPE)
report on behalf of the Fermi GBM Team: 


"At 12:55:08 UT on 28 October 2008, the Fermi GBM triggered
and located GRB 081028B (trigger 246891309 / 081028538).
The on-ground calculated location, using the GBM trigger data, 
is RA = 19.8, Dec = -23.5 (J2000 degrees,
equivalent to 1h 19m, -23d 30'), with an uncertainty
of 6.2 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.

This long GRB is single peaked, with an estimated T90 (50-300 keV)
of about 20 s. The time-averaged spectrum (10-1000 keV) from T0-5.1 s to
T0+7.1 s is well fit by a power law function with an exponential 
high-energy cutoff.  The cutoff energy, parameterized as Epeak, 
is 70 +/- 4 keV with a power law index of -0.55 +/- 0.16. 

The fluence (10-1000 keV) in this time interval is 
(2.0 +/- 0.3)E-06 erg/cm^2. The 1 sec peak photon flux measured starting
from T0+1.5 s in the 10-1000 keV band is 6.9 +/- 0.5 ph/s/cm^2.


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