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GCN Circular 20530

Subject
GRB 170126A: Swift detection of a burst with an optical counterpart
Date
2017-01-26T11:44:29Z (7 years ago)
From
Scott Barthelmy at NASA/GSFC <scott@milkyway.gsfc.nasa.gov>
D. Kocevski (NASA/MSFC), S. D. Barthelmy (GSFC),
A. A. Breeveld (UCL-MSSL), D. N. Burrows (PSU), A. D'Ai (INAF-IASFPA),
S. W. K Emery (UCL-MSSL), J. A. Kennea (PSU),
F. E. Marshall (NASA/GSFC) and M. H. Siegel (PSU) report on behalf of
the Swift Team:

At 11:30:42 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 170126A (trigger=735188).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 263.579, -64.757 which is 
   RA(J2000)  =  17h 34m 19s
   Dec(J2000) = -64d 45' 26"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows a single FRED-like peak
structure with a duration of about 15 sec.  The peak count rate
was ~3000 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 11:32:09.4 UT, 87.1 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 263.63341, -64.76046 which is
equivalent to:
   RA(J2000)  = 17h 34m 32.02s
   Dec(J2000) = -64d 45' 37.7"
with an uncertainty of 4.2 arcseconds (radius, 90% containment). This
location is 84 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. No
spectrum from the promptly downlinked event data is yet available to
determine the column density. 

UVOT took a finding chart exposure of 131 seconds with the White filter
starting 90 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	17:34:31.95 = 263.63311
  DEC(J2000) = -64:45:37.0  = -64.76027
with a 90%-confidence error radius of about 0.62 arc sec. This position is 0.9
arc sec. from the center of the XRT error circle. The estimated magnitude is
18.12 with a 1-sigma error of about  0.15. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.10. 

Burst Advocate for this burst is D. Kocevski (dankocevski AT gmail.com). 
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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