[vsnet-grb-info 17113] GRB 151021B: Fermi GBM detection

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  18434
SUBJECT: GRB 151021B: Fermi GBM detection
DATE:    15/10/22 04:10:01 GMT
FROM:    Peter Veres at UAH  <veresp at gmail.com>

P. Veres (UAH) and C. Meegan (UAH) report on behalf of the Fermi GBM Team:

"At 18:59:28.92 UT on 21 October 2015, the Fermi Gamma-Ray Burst
Monitor triggered and located GRB 151021B (trigger 467146772 /
151021791).

The on-ground calculated location, using the GBM trigger data, is RA =
104.340, DEC = -10.960 (J2000 degrees, equivalent to 06 h 57 m, -10 d
58 '), with an uncertainty of 1.20 degrees (radius, 1-sigma
containment, statistical only; there is additionally a systematic
error which we have characterized as a core-plus-tail model, with 90%
of GRBs having a 3.7 deg error and a small tail suffering a larger
than 10 deg systematic error. [Connaughton et al. 2015, ApJS, 216, 32]
).

The angle from the Fermi LAT boresight at the GBM trigger time is 83 degrees.

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

The GBM light curve consists of a single pulse with fast rise and
exponential decay with a duration (T90) of about 7.2 s (50-300 keV).
The time-averaged spectrum from T0-0.1 s to T0+9.1 s is well fit by a
power law function with an exponential high-energy cutoff. The power
law index is -0.67 +/- 0.03 and the cutoff energy, parameterized as
Epeak, is 270 +/- 10 keV.

A Band function fits the spectrum equally well with Epeak = 241 +/- 13
keV, alpha = -0.61 +/- 0.04 and beta = -2.6 +/- 0.2.

The event fluence (10-1000 keV) in this time interval is (1.226 +/-
0.004)E-05 erg/cm^2. The 1-sec peak photon flux measured starting from
T0+0.77 s in the 10-1000 keV band is 21.5 +/- 0.4 ph/s/cm^2.

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