[vsnet-grb-info 9080] GRB 100401A: Fermi GBM detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  10568
SUBJECT: GRB 100401A: Fermi GBM detection
DATE:    10/04/02 22:59:08 GMT
FROM:    Adam Goldstein at Fermi-GBM/UAH  <adam.m.goldstein at msfc.nasa.gov>

A. Goldstein (UAH) and D. Gruber (MPE) 
report on behalf of the Fermi GBM Team: 

"At 07:07:32.24 UT on 1 April 2010, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 100401A (trigger 291798454 / 100401297)
which was also detected by the Swift-BAT (J.R. Cummings et al. 2010,
GCN 10567).  The GBM on-ground location is consistent with the 
Swift-BAT position. The angle from the Fermi LAT boresight is 45 degrees.

The GBM light curve consists of an initial bright pulse at trigger time
lasting ~4 s followed by a second, much softer pulse of ~30 s in duration,
approximately 65 s after trigger time. The total duration (T90) is 
estimated to be about 100 s (8-1000 keV). The time-averaged spectrum of 
the first pulse from T0-1.9 s to T0+3.2 s is best fit by a power law 
function with an exponential high energy cutoff.  The power law index is 
-1.49 +/- 0.17 and the cutoff energy, parameterized as Epeak, is 
144.90 +/- 62.20 keV (chi squared 439 for 483 d.o.f.). The first 
pulse is equally well fit by a simple power law with index 
-1.77 +/- 0.06 (chi squared 444 for 484 d.o.f.).  The 
time-averaged spectrum of the second pulse from T0+74.9 s to 
T0+98.4 s is well fit by a power law function with an exponential
high energy cutoff.  The power law index is -1.52 +/- 0.39 and
the cutoff energy, parameterized as Epeak, is 29.34 +/- 8.96 keV
(chi squared 511 for 483 d.o.f.).  The second pulse is equally well
fit by a simple power law with index -2.16 +/- 0.11 (chi squared 
514 for 484 d.o.f.).

The event fluence (8-1000 keV) over the entire emission is 
(2.39 +/- 0.05)E-06 erg/cm^2. The 1-sec peak photon flux measured 
starting from T0-1.4 s in the 8-1000 keV band 
is 3.61 +/- 0.16 ph/s/cm^2.

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