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GCN Circular 9223

Subject
GRB 090424: Swift detection of a burst with an optical counterpart
Date
2009-04-24T14:23:57Z (15 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@lheamail.gsfc.nasa.gov>
J. K. Cannizzo (NASA/UMBC), S. D. Barthelmy (GSFC),
A. P. Beardmore (U Leicester), D. N. Burrows (PSU),
P.A. Curran (MSSL-UCL), P. A. Evans (U Leicester),
N. Gehrels (NASA/GSFC), C. Gronwall (PSU), C. Guidorzi (U Ferrara),
S. T. Holland (CRESST/USRA/GSFC), J. A. Kennea (PSU),
H. A. Krimm (CRESST/GSFC/USRA), J. Mao (INAF-OAB),
R. Margutti (Univ Bicocca&OAB), F. E. Marshall (NASA/GSFC),
P. T. O'Brien (U Leicester), K. L. Page (U Leicester),
P. Romano (INAF-IASFPA), B. A. Rowlinson (U Leicester),
M. H. Siegel (PSU), M. C. Stroh (PSU), G. Tagliaferri (INAF-OAB) and
L. Vetere (PSU) report on behalf of the Swift Team:

At 14:12:09 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 090424 (trigger=350311).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 189.538, +16.829 which is 
   RA(J2000)  =  12h 38m 09s
   Dec(J2000) = +16d 49' 46"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows several bright peaks
in the first 5 seconds, and then several smaller peaks at T+8, +15,
and +50 sec.  Total duration of about 60 sec.  The peak count rate
was ~50000 counts/sec (15-350 keV), at ~3 sec after the trigger. 

The XRT began observing the field at 14:13:33.8 UT, 84.5 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 189.5213, +16.8364 which is equivalent to:
   RA(J2000)  = 12h 38m 05.11s
   Dec(J2000) = +16d 50' 11.0"
with an uncertainty of 4.8 arcseconds (radius, 90% containment). This
location is 63 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 91 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	12:38:05.11 = 189.52128
  DEC(J2000) = +16:50:15.1  = 16.83753
with a 90%-confidence error radius of about 0.74 arc sec. This position is 4.1
arc sec. from the center of the XRT error circle. The estimated magnitude is
15.29 with a 1-sigma error of about 0.14. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.03. 

Burst Advocate for this burst is J. K. Cannizzo (cannizzo AT milkyway.gsfc.nasa.gov). 
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.)
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