[vsnet-grb-info 14051] GRB 131024A: Swift detection of a burst

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  15365
SUBJECT: GRB 131024A: Swift detection of a burst
DATE:    13/10/24 12:37:23 GMT
FROM:    David Palmer at LANL  <palmer at lanl.gov>

J. L. Racusin (NASA/GSFC), D. N. Burrows (PSU),
N. Gehrels (NASA/GSFC), H. A. Krimm (CRESST/GSFC/USRA),
A. Maselli (INAF-IASFPA), K. L. Page (U Leicester),
D. M. Palmer (LANL), P. Romano (INAF-IASFPA), M. H. Siegel (PSU),
E. Troja (NASA/GSFC/UMCP) and T. N. Ukwatta (MSU) report on behalf of
the Swift Team:

At 12:26:20 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 131024A (trigger=575707).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 290.464, -64.603 which is 
   RA(J2000) = 19h 21m 51s
   Dec(J2000) = -64d 36' 08"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  As is usual with an image trigger, the available
BAT light curve shows no significant structure. 

The XRT began observing the field at 12:28:34.2 UT, 133.5 seconds after
the BAT trigger. Using promptly downlinked data we find a fading,
uncatalogued X-ray source located at RA, Dec 290.48228, -64.60181 which
is equivalent to:
   RA(J2000)  = 19h 21m 55.75s
   Dec(J2000) = -64d 36' 06.5"
with an uncertainty of 4.0 arcseconds (radius, 90% containment). This
location is 28 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 4.45
x 10^20 cm^-2 (Kalberla et al. 2005). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 136 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
0.05. 

Burst Advocate for this burst is J. L. Racusin (judith.racusin AT 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.)