[vsnet-grb-info 3560] GRB 060804: Swift detection of a burst with a possible UVOT counterpart

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  5394
SUBJECT: GRB 060804: Swift detection of a burst with a possible UVOT counterpart
DATE:    06/08/04 08:10:13 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <scott at lheamail.gsfc.nasa.gov>

H. Z. Ziaeepour (UCL-MSSL), S. D. Barthelmy (GSFC),
D. N. Burrows (PSU), J. R. Cummings (NASA/UMD),
N. Gehrels (NASA/GSFC), C. Guidorzi (Univ Bicocca&INAF-OAB),
J. A. Kennea (PSU), C. B. Markwardt (GSFC/UMD),
M. J. Page (UCL-MSSL), K. L. Page (U Leicester), D. M. Palmer (LANL),
G. Sato (GSFC/ISAS), M. Stamatikos (NASA/ORAU) and
G. Tagliaferri (INAF-OAB) report on behalf of the Swift Team:

At 07:28:19 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 060804 (trigger=222546).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is RA,Dec 112.201, -27.231 
{07h 28m 48s, -27d 13' 52"} (J2000) with an uncertainty of 3 arcmin
(radius, 90% containment, including systematic uncertainty). 
The BAT light curve shows a single peak with a duration of about 10 sec. 
The peak count rate was ~600 counts/sec (15-350 keV), at ~5 sec
after the trigger. 

The XRT began taking data at 07:30:21 UT, 121 seconds after the BAT
trigger. Although the XRT on-board centroid algorithm did not find a
source in the image, ground analysis revealed an uncatalogued point
source at a position of RA(J2000) = 07h 28m 49.40s, Dec(J2000) = -27d
12' 58.9", with an estimated error of 3.9 arcsec radius (90%
containment). 

UVOT took a finding chart exposure of 100 seconds with the White
(160-650 nm) filter starting 128 seconds after the BAT trigger. A
possible afterglow candidate is seen in the 2.7'x2.7' sub-image
with an estimated magnitude of V=17 at position RA(J2000) =
07h 28m 49.36s Dec(J2000) = -27d 12' 56.7" with an estimated error of 1". 

The Be star SPH 10 is in the BAT error circle.  However, it is 
inconsistent with the XRT and UVOT source location (2 arcminutes) 
and is therefore unlikely to be associated with the burst.