[vsnet-grb-info 3148] GRB(?) 060421: Swift detection of a burst

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  4985
SUBJECT: GRB(?) 060421: Swift detection of a burst
DATE:    06/04/21 01:15:46 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <Scott at lheamail.gsfc.nasa.gov>

M. R. Goad (U Leicester), L. M. Barbier (NASA/GSFC),
S. D. Barthelmy (GSFC), A. P. Beardmore (U Leicester),
P. J. Brown (PSU), D. N. Burrows (PSU), J. R. Cummings (NASA/ORAU),
N. Gehrels (NASA/GSFC), S. T. Holland (GSFC/USRA), J. A. Kennea (PSU)
and D. M. Palmer (LANL) report on behalf of the Swift Team:

At 00:39:23 UT, the Swift Burst Alert Telescope (BAT) triggered and located
GRB 060421 (trigger=206257).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is RA,Dec 343.630,+62.727
{22h 54m 31s, +62d 43' 37"} (J2000) with an uncertainty of 3 arcmin
(radius, 90% containment, including systematic uncertainty). 
The BAT light curve shows a multi-peak structure starting at about T-5sec
and lasting to at least T+20 sec (a duration of about 25 sec). 
The peak count rate was ~6000 counts/sec (15-350 keV), at ~3 sec after
the trigger. 

This source is coincident with the Cepheus OB3 molecular cloud 
association in our Galaxy.  Therefore it is possible that this 
burst (galactic long,lat = 109.99, +2.83) was from 
a galactic source. 

The XRT began taking data at 00:40:50 UT, 88 seconds after the BAT
trigger. The XRT on-board centroid algorithm did not find a source in
the image and no prompt position is available. Analysis of
down-linked image data reveals no obvious X-ray point source in the
field. We are waiting for the full down-linked dataset to detect and 
determine a position for the source, and to determine the nature of 
this source. 

UVOT took a finding chart exposure of 400 seconds with the V filter
starting 85 seconds after the BAT trigger. No afterglow candidate has
been found in the initial data products. The 2.7'x2.7' sub-image
covers 25% of the BAT error circle. The typical 3-sigma upper limit
has been about 18.5 mag. The 8'x8' region for the list of sources
generated on-board covers 100% of the BAT error circle. The limiting
magnitude is expected to be about 17.7. No correction has been made
for the large, but uncertain extinction expected. 

Results from analysis of downlinked data will not be available until
approximately 09:00UT.