TITLE:   GCN CIRCULAR
NUMBER:  9086
SUBJECT: GRB 090404: Swift detection of a burst
DATE:    09/04/04 16:07:58 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),
N. Gehrels (NASA/GSFC), C. Guidorzi (U Ferrara),
S. T. Holland (CRESST/USRA/GSFC), J. A. Kennea (PSU),
C. B. Markwardt (CRESST/GSFC/UMD), F. E. Marshall (NASA/GSFC),
P. T. O'Brien (U Leicester), S. R. Oates (UCL-MSSL),
K. L. Page (U Leicester), D. M. Palmer (LANL) and
B. Sbarufatti (INAF-IASFPA) report on behalf of the Swift Team:

At 15:56:30 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 090404 (trigger=348428).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 239.218, +35.500 which is 
   RA(J2000) = 15h 56m 52s
   Dec(J2000) = +35d 29' 59"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a multiply-peaked
structure with a duration of about 80 sec and possible activity 
out to T+100 sec.  The peak count rate was ~3500 counts/sec 
(15-350 keV), at ~17 sec after the trigger. 

The XRT began observing the field at 15:57:57.8 UT, 87.3 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 239.2351, +35.5173 which is equivalent to:
   RA(J2000)  = 15h 56m 56.42s
   Dec(J2000) = +35d 31' 02.2"
with an uncertainty of 5.0 arcseconds (radius, 90% containment). This
location is 79 arcseconds from the BAT onboard position, within the BAT
error circle. No event data are yet available to determine the column
density using X-ray spectroscopy. 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 96 seconds after the BAT trigger. No credible 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 typical 3-sigma upper limit has been about 19.6 mag. 
The 8'x8' region for the list of sources generated on-board covers 100% of the
XRT error circle. The list of sources is typically complete to about 18 mag. No
correction has been made for the expected extinction corresponding to E(B-V) of
0.02. 

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.)