GCN Circular 17511

Valerie Connaughton and Peter Jenke (UAH) and Adam Goldstein (NASA MSFC)
report on behalf of the Fermi GBM Team:

"At 01:04:28.65 UT on 01 March 2015, the Fermi Gamma-Ray Burst Monitor
triggered and located GRB 150301A (trigger 446864671 / 150301045)
which was also detected by the Swift/BAT (Lien et al. 2015, GCN 17510
Not found
 
 
).
The GBM on-ground location is consistent with the Swift position.

The angle from the Fermi LAT boresight is 105 degrees.

The GBM light curve consists of a single peak about 50 ms in duration.
The counts registered in the NaI detectors are strongly peaked in the
50 - 300 keV energy range typical for GRBs.  From the quicklook
data, the softness ratio for the event (20 - 100 keV / 100 - 500 keV)
is 0.4 +/- 0.3, typical for fairly hard GRBs.  By contrast,
the corresponding softness ratios for recent triggers from
SGR 1935+2154 and AXP 4U 0142+61 were
4.4 +/- 1.8, 3.4 +/- 1.0, and 2.2 +/- 0.4.

The time-averaged spectrum from T0-0.016 s to T0+0.032 s is
best fit by a power law function with an exponential
high-energy cutoff.  The power law index is -0.53 +/- 0.35 and
the cutoff energy, parameterized as Epeak, is 185 +/- 49 keV.

The event fluence (10-1000 keV) in this time interval is
(1.2 +/- 0.2)E-07 erg/cm^2. The 16-msec peak photon flux measured
starting from T0-0.016 s in the 10-1000 keV band
is 29 +/- 4 ph/s/cm^2.

The spectral characteristics of this burst are more like a GRB than
an SGR.  We think it is therefore unlikely that this event is a burst
from a new SGR and conclude that it is, instead, a short GRB.


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