[vsnet-grb-info 10584] GRB 110426A: Fermi GBM detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  12013
SUBJECT: GRB 110426A: Fermi GBM detection
DATE:    11/05/09 23:47:06 GMT
FROM:    Alexander van der Horst at NASA/MSFC  <Alexander.J.VanDerHorst at nasa.gov>

A.J. van der Horst and A. Camero-Arranz (USRA) report on behalf of
the Fermi GBM Team:

"At 15:06:26.61 UT on 26 April 2011, the Fermi Gamma-Ray Burst Monitor
triggered on GRB 110426A (trigger 325523188 / 110426629). The on-ground
calculated location, using the GBM trigger data, is RA = 219.9, Dec = -8.7
(J2000 degrees, equivalent to 14h40m, -8d43'), with an uncertainty of
2.1 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 88 degrees.

This is most likely the same source as the one that MAXI/GSC reported
in GCN 11980. Although MAXI/GSC triggered 130 seconds later than GBM on
GRB 110426A, the locations obtained by both instruments are consistent.
The GBM light curve consists of multiple peaks with a duration (T90) of
328 +/- 3 s (50-300 keV), indicating that the source was still active
when MAXI/GSC detected it.

The time-averaged spectrum from T0-4.1 s to T0+327.7 s is adequately fit
by a simple power law function with index -2.28 +/- 0.01. The event fluence
(10-1000 keV) in this time interval is (4.54 +/- 0.06)E-5 erg/cm^2.
The 1-sec peak photon flux measured starting from T0+216.1 s in the
10-1000 keV band is 6.7 +/- 0.4 ph/s/cm^2.

We note that there is bursting emission detected in GBM starting ~40
minutes before the trigger. This emission is significantly softer than
the ~6 minute emission episode after the GBM trigger time. The start of
the spectrally soft bursts is consistent with Sco X-1 coming out of
Earth occultation. The GRB 110426A location, however, is not consistent
with Sco X-1 and thus a separate source.

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