[vsnet-grb-info 7169] GRB 081226C: Fermi GBM detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  8750
SUBJECT: GRB 081226C: Fermi GBM detection
DATE:    08/12/29 15:22:32 GMT
FROM:    Elisabetta Bissaldi at MPE  <ebs at mpe.mpg.de>

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


"At 03:44:52.41 UT on 26 December 2008, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 081226C (trigger 251955893 / 081226156).
The on-ground calculated location, using the GBM trigger 
data, is RA = 189.4, DEC = 27.8 (J2000 degrees, 
equivalent to 12h 38m, 27d 48'), with an uncertainty 
of 3.6 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 54 degrees.

This long GRB consists of two main emission pulses plus
weak untriggered emission starting at about T0-45 s
and lasting about 25 s.
The total event duration (T90) is about 60 s (8-1000 keV).

The time-averaged spectrum from T0-3.6 s to T0+10.7 s is
best fit by a power law function with an
exponential high energy cutoff. The power law index is
-1.04 +/- 0.11 and the cutoff energy, parameterized as
Epeak, is 82 +/- 7 keV (chi squared 395 for 362 d.o.f.).
The time-averaged spectrum of the precursor from T0-48.6 s
to T0-28.2 s is also well fit by a power law function with an
exponential high energy cutoff. The power law index is
-1.14 +/- 0.23 and the cutoff energy, parameterized as Epeak,
is 71 +/- 11 keV (chi squared 370 for 363 d.o.f.).

The event fluence (8-1000 keV) from T0-3.6 s to T0+10.7 is
(2.32 +/- 0.24)E-06 erg/cm^2. The 1-sec peak photon flux measured
starting from T0+6.6 s in the 8-1000 keV band
is 4.5 +/- 0.8 ph/s/cm^2.


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