TITLE:   GCN CIRCULAR
NUMBER:  8691
SUBJECT: GRB 081222: Swift detection of a burst with a bright optical afterglow
DATE:    08/12/22 05:28:23 GMT
FROM:    David Palmer at LANL  <palmer@lanl.gov>

D. Grupe (PSU), M. M. Chester (PSU), J. R. Cummings (NASA/UMBC),
N. Gehrels (NASA/GSFC), C. B. Markwardt (CRESST/GSFC/UMD),
D. M. Palmer (LANL), J. L. Racusin (PSU), M. Stamatikos (NASA/ORAU)
and M. C. Stroh (PSU) report on behalf of the Swift Team:

At 04:53:59 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 081222 (trigger=337914).  Swift slewed immediately to the 
burst.  The BAT on-board calculated location is 
RA, Dec 22.751, -34.128 which is 
   RA(J2000) = 01h 31m 00s
   Dec(J2000) = -34d 07' 41"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a multipeaked
structure with a duration of about 20 sec.  The peak count rate
was ~10000 counts/sec (15-350 keV), at 3 sec after the trigger. 

The XRT began observing the field at 04:54:51.7 UT, 51.8 seconds after
the BAT trigger. Using promptly downlinked data we find a bright, fading,
uncatalogued X-ray source located at RA, Dec 22.74067, -34.09556 which
is equivalent to:
   RA(J2000)  = 01h 30m 57.76s
   Dec(J2000) = -34d 05' 44.0"
with an uncertainty of 3.6 arcseconds (radius, 90% containment). This
location is 120 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 consistent with the Galactic value of
2.24e+20 cm^-2 (Kalberla et al. 2005). 

The initial flux in the 2.5 s image was 3.91e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White
filter  starting 60 seconds after the BAT trigger. There is a
candidate afterglow in  the rapidly available 2.7'x2.7' sub-image
consistent with the XRT candidate.  A precise location and magnitude
estimate are not available at this time. 

This burst is consistent with the Fermi GBM burst   Trigger 251614441. 

Burst Advocate for this burst is D. Grupe (grupe AT astro.psu.edu). 
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.)