GCN Circular 6640

H. Ziaeepour (UCL-MSSL), S. D. Barthelmy (GSFC),
A. P. Beardmore (U Leicester), D. N. Burrows (PSU),
P. A. Evans (U Leicester), K. L. Page (U Leicester) and
P. Schady (MSSL-UCL) report on behalf of the Swift Team:

At 10:33:48 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 070721B (trigger=285654).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 33.131, -2.184 (J2000) with an uncertainty of 3 arcmin
(radius, 90% containment, including systematic uncertainty). 
Like the previous trigger, there continues be a problem with the messages,
so we are not able to say anything about the lightcurve at this time. 

The XRT found a bright, uncatalogued source at 
RA(J2000) = 33.13506 
DEC(J2000) = -2.19602
which is  45.7 arcseconds from the BAT position. We do not have
an  error estimate, but the typical uncertainty for on-board centroids
is 6 arcseconds. The source flux was about 1.296e-09 cgs. While we don't
have the usual GCN notices for this trigger, the realtime
telemetry from the spacecraft indicates that the source is fading. 

At the moment no UVOT data are available. We are waiting for the next
Malindi pass to download more data. 

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.)