[vsnet-grb-info 12686] GRB 121209A: Swift detection of a burst

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  14045
SUBJECT: GRB 121209A: Swift detection of a burst
DATE:    12/12/09 22:09:02 GMT
FROM:    Scott Barthelmy at NASA/GSFC  <scott at milkyway.gsfc.nasa.gov>

A. Maselli (INAF-IASFPA), S. D. Barthelmy (GSFC),
W. H. Baumgartner (GSFC/UMBC), D. N. Burrows (PSU),
J. A. Kennea (PSU), N. P. M. Kuin (UCL-MSSL),
C. B. Markwardt (NASA/GSFC), F. E. Marshall (NASA/GSFC),
D. M. Palmer (LANL), B. Sbarufatti (INAF-OAB/PSU), M. H. Siegel (PSU)
and E. Troja (NASA/GSFC/UMCP) report on behalf of the Swift Team:

At 21:59:11 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 121209A (trigger=540964).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 326.801, -8.244 which is 
   RA(J2000)  =  21h 47m 12s
   Dec(J2000) = -08d 14' 39"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows multiple peaks
with a total duration of about 60 sec.  The peak count rate
was ~3300 counts/sec (15-350 keV), at ~20 sec after the trigger. 

The XRT began observing the field at 22:00:43.3 UT, 92.0 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 326.78917, -8.23262 which is equivalent
to:
   RA(J2000)  = 21h 47m 09.40s
   Dec(J2000) = -08d 13' 57.4"
with an uncertainty of 3.9 arcseconds (radius, 90% containment). This
location is 58 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.  We
cannot determine whether the source is fading at the present time. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density in excess of the Galactic value (3.81 x
10^20 cm^-2, Kalberla et al. 2005), with an excess column of 2.8
(+2.58/-2.19) x 10^21 cm^-2 (90% confidence). 

UVOT data is not yet available. 

Burst Advocate for this burst is A. Maselli (maselli AT ifc.inaf.it). 
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.)