[vsnet-grb-info 5680] GRB 080229: Swift detection of a bright burst

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  7335
SUBJECT: GRB 080229: Swift detection of a bright burst
DATE:    08/02/29 17:31:15 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <scott at lheamail.gsfc.nasa.gov>

J. K. Cannizzo (NASA/UMBC), S. D. Barthelmy (GSFC),
A. P. Beardmore (U Leicester), J. R. Cummings (NASA/UMBC),
P. A. Evans (U Leicester), O. Godet (U Leicester), C. Gronwall (PSU),
S. T. Holland (CRESST/USRA/GSFC), E. A. Hoversten (PSU),
S. Immler (CRESST/GSFC/UMD), J. A. Kennea (PSU),
V. Mangano (INAF-IASFPA), C. B. Markwardt (CRESST/GSFC/UMD),
K. M. McLean (GSFC/UMD), A. Moretti (INAF-OAB),
P. T. O'Brien (U Leicester), J. P. Osborne (U Leicester),
C. Pagani (PSU), K. L. Page (U Leicester), D. M. Palmer (LANL),
A. M. Parsons (GSFC), T. Sakamoto (NASA/UMBC), G. Sato (GSFC/ISAS),
B. Sbarufatti (INAF-IASFPA), M. Stamatikos (NASA/ORAU),
R. L. C. Starling (U Leicester), G. Stratta (ASDC) and
E. Troja (U Leicester/INAF-IASFPa) report on behalf of the Swift
Team:

At 17:04:59 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 080229 (trigger=304379).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 228.217, -14.712 which is 
   RA(J2000)  =  15h 12m 52s
   Dec(J2000) = -14d 42' 43"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed three or four bright 
peaks with the brightest at ~T+40 sec with a duration of about 60 sec. 
The peak count rate was ~7000 counts/sec (15-350 keV), at ~40 sec
after the trigger. 

The XRT began observing the field at 17:06:29.9 UT, 90.3 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source with an enhanced position: RA, Dec 228.21888,
-14.70536 which is equivalent to:
   RA(J2000)  = 15h 12m 52.53s
   Dec(J2000) = -14d 42' 19.3"
with an uncertainty of 2.7 arcseconds (radius, 90% containment). This
location is 24 arcseconds from the BAT onboard position, within the BAT
error circle. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of
8.97e+20 cm^-2 (Kalberla et al. 2005), so we cannot constrain the
redshift at this time using the relation from Grupe et al. (2007). A
summary of the promptly downlinked data is given at
http://www.swift.ac.uk/sper/304379/. 

The initial flux in the 2.5 s image was 5.98e-09 erg cm^-2 s^-2 (0.2-10
keV). 

UVOT took a finding chart exposure of 100 seconds with the White
(160-650 nm) filter starting 100 seconds after the BAT trigger. A 400
second image in V band was also taken 207 seconds after the trigger. 
No afterglow candidate has been found in the either image. The
2.7'x2.7' sub-image covers 100% of the XRT error circle. The typical
3-sigma upper limit has been about 18.5 mag in white and 18.0 in V. 
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 0.15. There is a F0
star with R1~13.3 in the USNO catalog nearby the XRT position which
appears in DSS images. 

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.)