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GCN Circular 9963

GRB 090929B: Swift detection of a burst
2009-09-29T10:37:12Z (15 years ago)
David Palmer at LANL <>
C. Pagani (PSU), A. P. Beardmore (U Leicester), S. Campana (INAF-OAB),
V. D'Elia (ASDC), C. Gronwall (PSU), D. Grupe (PSU),
C. Guidorzi (U Ferrara), S. T. Holland (CRESST/USRA/GSFC),
N. P. M. Kuin (MSSL), J. Mao (INAF-OAB), P. T. O'Brien (U Leicester),
J. P. Osborne (U Leicester), K. L. Page (U Leicester),
D. M. Palmer (LANL), P. Romano (INAF-IASFPA),
B. Sbarufatti (INAF-IASFPA), T. N. Ukwatta (GSFC/GWU) and
L. Vetere (PSU) report on behalf of the Swift Team:

At 10:09:07 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 090929B (trigger=371050).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 117.705, -0.632 which is 
   RA(J2000) = 07h 50m 49s
   Dec(J2000) = -00d 37' 55"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a complex structure
with most activity in multiple peaks from T-10 sec to T+50 s, and additional
peaks at T+150 sec, during the XRT observations.  The peak count rate
was ~7000 counts/sec (15-350 keV), at ~40 sec after the trigger. 

The XRT began observing the field at 10:10:31.3 UT, 84.1 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 117.7202, -0.6574 which is equivalent to:
   RA(J2000)  = 07h 50m 52.84s
   Dec(J2000) = -00d 39' 26.6"
with an uncertainty of 5.3 arcseconds (radius, 90% containment). This
location is 106 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. 

The initial flux in the 2.5 s image was 1.49e-09 erg cm^-2 s^-1 (0.2-10

UVOT took a finding chart exposure of  97 seconds with the White
filter  starting 93 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  0.07.  We note there is a bright (10th mag) star less than
2 arcsec from the XRT position which complicates the analysis of the
UVOT data. 

Burst Advocate for this burst is C. Pagani (pagani AT 
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:
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