GCN Circular 6653

A. Copete, J. Grindlay, and J. Hong (Harvard),
S. Barthelmy and N. Gehrels (NASA/GSFC)

We report on the first GRB found solely from imaging using BAT slew data,
from a test run carried out in March 2007 of what will become the BAT Slew
Survey (BATSS; Grindlay, astro-ph# 0704.3294). A 58sec-long slew which
began on 2007-03-26 16:29:10 UT, from a prior SAA passage onto Swift
observation number 00271019007, included a burst (hereafter referred to as
GRB 070326) detected independently at 8.9 sigma and 6.9 sigma in the
15-50keV and 50-150keV energy bands, respectively. The GRB T0 occurred 2
sec after the start of the slew. The averaged position of the burst was
found to be:
  RA(J2000) = 2h 41m 20.8s
  Dec(J2000) = -66d 59' 21"
with an uncertainty radius of 3.9 arcmin (99% confidence).
The time-averaged coding fraction at the burst location was 65% and the
exposure time was 58.0 sec.

The mask-weighted lightcurve features a single 17.3 sec peak, rising
sharply over 3 sec and then followed by a steady, approximately
exponential decay. Preliminary spectral analysis over the total duration
of the burst shows a 15-150 keV spectrum that is best fit with a simple
power law, with photon index of 1.44 +- 0.17. The burst fluence was
estimated at (3.45 +- 0.37) x 10^-7 erg/cm2 (15-150 keV).

BATSS will begin regular operations as soon as its pipeline processing
systems developed at Harvard are implemented at GSFC. Based on this
initial 7d of test slew processing and one new GRB detected, the overall
rate of Swift GRBs could increase by ~20-40%. Follow-up pointings with XRT
could be commanded on the next satellite data pass, or with ~1-4h delay.