TITLE:   GCN CIRCULAR
NUMBER:  9101
SUBJECT: GRB 090407: Swift detection of a burst
DATE:    09/04/07 10:48:08 GMT
FROM:    David Burrows at PSU/Swift  <dxb15@psu.edu>

H. Ziaeepour (UCL-MSSL), S. D. Barthelmy (GSFC),
W. H. Baumgartner (GSFC/UMBC), A. P. Beardmore (U Leicester),
D. N. Burrows (PSU), P. A. Evans (U Leicester),
N. Gehrels (NASA/GSFC), O. Godet (U Leicester),
C. Guidorzi (U Ferrara), S. T. Holland (CRESST/USRA/GSFC),
J. A. Kennea (PSU), N. P. M. Kuin (MSSL), J. Mao (INAF-OAB),
P. T. O'Brien (U Leicester), S. R. Oates (UCL-MSSL),
J. P. Osborne (U Leicester), K. L. Page (U Leicester),
D. M. Palmer (LANL), P. Romano (INAF-IASFPA),
B. A. Rowlinson (U Leicester), B. Sbarufatti (INAF-IASFPA),
P. Schady (MSSL-UCL) and G. Stratta (ASDC) report on behalf of the
Swift Team:

At 10:28:25 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 090407 (trigger=348650).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 68.959, -12.665 which is 
   RA(J2000) = 04h 35m 50s
   Dec(J2000) = -12d 39' 53"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a multiple-peaked
structure with a duration of at least 150 sec, including a small
peak at T+135 sec, during the XRT/UVOT observations.  The peak count rate
was ~2390 counts/sec (15-350 keV), at ~1 sec after the trigger. 

The XRT began observing the field at 10:29:58.7 UT, 93.0 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source located at RA, Dec 68.98074, -12.67921 which
is equivalent to:
   RA(J2000)  = 04h 35m 55.38s
   Dec(J2000) = -12d 40' 45.2"
with an uncertainty of 3.8 arcseconds (radius, 90% containment). This
location is 91 arcseconds from the BAT onboard position, within the BAT
error circle. This position may be improved as more data are received;
the latest position is available at http://www.swift.ac.uk/sper. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density in excess of the Galactic value (3.68e+20
cm^-2, Kalberla et al. 2005), with an excess column of 2.5
(+1.79/-1.62) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White 
filter  starting 97 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 25% of the BAT error circle and 0% 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  BAT and XRT error circles. 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 0.07. 

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.)