[vsnet-grb-info 18927] GRB 170111A: Swift detection of a burst

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  20423
SUBJECT: GRB 170111A: Swift detection of a burst
DATE:    17/01/11 00:53:54 GMT
FROM:    David Palmer at LANL  <palmer at lanl.gov>

A. P. Beardmore (U Leicester), D. N. Burrows (PSU), C. Gronwall (PSU),
J. A. Kennea (PSU), A. Y. Lien (GSFC/UMBC), D. M. Palmer (LANL) and
M. H. Siegel (PSU) report on behalf of the Swift Team:

At 00:33:28 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 170111A (trigger=731887).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 20.717, -32.540 which is 
   RA(J2000) = 01h 22m 52s
   Dec(J2000) = -32d 32' 23"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a single peak
structure with a duration of about 40 sec.  The peak count rate
was ~700 counts/sec (15-350 keV), at ~2 sec after the trigger. 

The XRT began observing the field at 00:35:14.8 UT, 106.7 seconds after
the BAT trigger. Using promptly downlinked data we find a variable, uncatalogued
X-ray source with an enhanced position: RA, Dec 20.6981, -32.5653 which
is equivalent to:
   RA(J2000)  = 01h 22m 47.56s
   Dec(J2000) = -32d 33' 55.1"
with an uncertainty of 2.1 arcseconds (radius, 90% containment). This
location is 107 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 (3.10 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 4.1
(+2.60/-2.25) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White
filter  starting 112 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  approximately 70% 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 0.03. 

Burst Advocate for this burst is A. P. Beardmore (apb AT star.le.ac.uk). 
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.)