TITLE:   GCN CIRCULAR
NUMBER:  6654
SUBJECT: GRB 070724: Swift detection of a burst
DATE:    07/07/24 11:22:00 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <scott@lheamail.gsfc.nasa.gov>

H. Ziaeepour (UCL-MSSL), S. D. Barthelmy (GSFC),
A. P. Beardmore (U Leicester), D. N. Burrows (PSU),
M. De Pasquale (UCL-MSSL), P. A. Evans (U Leicester),
N. Gehrels (NASA/GSFC), S. T. Holland (CRESST/GSFC/USRA),
H. A. Krimm (GSFC/USRA), V. Mangano (INAF-IASFPA),
F. E. Marshall (NASA/GSFC), P. T. O'Brien (U Leicester),
J. P. Osborne (U Leicester), C. Pagani (PSU),
K. L. Page (U Leicester), D. M. Palmer (LANL), A. M. Parsons (GSFC),
P. Romano (Univ. Bicocca & INAF-OAB), B. Sbarufatti (INAF-IASFPA),
P. Schady (MSSL-UCL), M. Stamatikos (NASA/ORAU) and
R. L. C. Starling (U Leicester) report on behalf of the Swift Team:

At 10:53:50 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 070724 (trigger=285948). Swift slewed immediately to the
burst. The BAT on-board calculated location is RA, Dec 27.818,
-18.622 which is
  RA(J2000) = 01h 51m 16s
  Dec(J2000) = -18d 37' 17"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The BAT light curve showed a strong spike
about one second long at T+0 sec. The peak count rate was ~2700
counts/sec (15-350 keV), at ~0 sec after the trigger. This could be a
short burst although the spectrum is not hard. 

The XRT began observing the field at 10:54:56 UT, 67 seconds after the
BAT trigger. Using prompt downlinked data, we find a variable, 
uncatalogued X-ray source located at RA, Dec 27.8077, -18.5951 which is
   RA(J2000)  = 01 51 13.86
   Dec(J2000) = -18 35 42.4
with an uncertainty of 4.7 arcsec (radius, 90% containment). 
This location is 102 arcseconds from the BAT on-board position,
within the BAT error circle. The initial flux in the 2.5s image
was 6.4e-10 erg/cm2/s (0.2-10 keV). 

UVOT took a finding chart exposure of 100s with the White filter
starting 75s after the BAT trigger. No afterglow candidate has been
found in the initial data products. The 2.7'x2.7' sub-image covers
100% of the XRT error circle. The 3-sigma upper limit is
about 19.2 mag. No correction has been made for the expected reddening 
of E(B-V) of 0.01. 

Burst Advocate for this burst is H. Ziaeepour (hz AT mssl.ucl.ac.uk). 
Please contact the BA by email if you require additional information
regarding Swift followup of this burst. In extremely urgent cases, after
trying the Burst Advocate, you can contact the Swift PI by phone (see
Swift TOO web site for information: http://www.swift.psu.edu/too.html.)