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GCN Circular 15283

Subject
GRB 131002A: Swift detection of a burst
Date
2013-10-02T07:49:31Z (10 years ago)
From
Caryl Gronwall at PSU/Swift-UVOT <caryl@astro.psu.edu>
B. N. Barlow (High Point University), V. D'Elia (ASDC), P. A. Evans (U  
Leicester), C. Gronwall (PSU), A. Y. Lien (NASA/GSFC/ORAU), D.  
Malesani (DARK/NBI), F. E. Marshall (NASA/GSFC), P. T. O'Brien (U  
Leicester), T. Sakamoto (AGU), M. H. Siegel (PSU) and M. C. Stroh  
(PSU) report on behalf of the Swift Team:
At 06:54:21 UT, the Swift Burst Alert Telescope (BAT) triggered and  
located GRB 131002A (trigger=572721). Swift slewed immediately to the  
burst. The BAT on-board calculated location is
RA, Dec 253.275, +82.057 which is
RA(J2000) = 16h 53m 06s
Dec(J2000) = +82d 03' 26"
with an uncertainty of 3 arcmin (radius, 90% containment, including  
systematic uncertainty). The BAT light curve showed two pulses with  
total duration of ~50 seconds. The first pulse happened at T0 lasting  
around 2 seconds, with peak count rate of ~3000 counts/sec (15-350  
keV). The second pulse happened at ~T+45 with a duration of around 15  
seconds and peak count rate ~2000 counts/sec (15-350 keV).
The XRT began observing the field at 06:55:27.9 UT, 66.7 seconds after  
the BAT trigger. Using promptly downlinked data we find a bright,  
fading, uncatalogued X-ray source with an enhanced position:
RA, Dec 253.2159, 82.0536 which is equivalent to:
RA(J2000) = 16h 52m 51.83s
Dec(J2000) = +82d 03' 13.0"
with an uncertainty of 2.0 arcseconds (radius, 90% containment). This  
location is 31 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 in excess of the Galactic value (5.56 x  
10^20 cm^-2, Kalberla et al. 2005), with an excess column of 2.6  
(+1.37/-1.25) x 10^21 cm^-2 (90% confidence).
The initial flux in the 2.5 s image was 9.38e-10 erg cm^-2 s^-1  
(0.2-10 keV).
UVOT took a finding chart exposure of 150 seconds with the White  
filter starting 869 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 0.08.
Burst Advocate for this burst is B. N. Barlow (bbarlow AT  
highpoint.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.)
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