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GCN Circular 17310

Subject
GRB 150120A: Swift detection of a possibly-short burst
Date
2015-01-20T03:12:39Z (10 years ago)
From
David Palmer at LANL <palmer@lanl.gov>
V. D'Elia (ASDC), D. N. Burrows (PSU), M. M. Chester (PSU),
N. Gehrels (NASA/GSFC), L. Izzo (URoma/ICRA),
F. E. Marshall (NASA/GSFC), D. M. Palmer (LANL), T. Sakamoto (AGU),
B. Sbarufatti (INAF-OAB/PSU) and M. H. Siegel (PSU) report on behalf
of the Swift Team:

At 02:57:46 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 150120A (trigger=627137).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 10.308, +33.981 which is 
   RA(J2000) = 00h 41m 14s
   Dec(J2000) = +33d 58' 52"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a single symmetric
peak structure with a duration of about 1.5 sec.  The peak count rate
was ~4000 counts/sec (15-350 keV), at ~0.5 sec after the trigger. 

The XRT began observing the field at 02:59:02.6 UT, 76.2 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 10.31883, 33.99480 which is equivalent
to:
   RA(J2000)  = 00h 41m 16.52s
   Dec(J2000) = +33d 59' 41.3"
with an uncertainty of 3.7 arcseconds (radius, 90% containment). This
location is 59 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 (7.86 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 6
(+5.52/-4.12) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 82 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
0.10. 

Burst Advocate for this burst is V. D'Elia (delia AT asdc.asi.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.)
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