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GCN Circular 22124

Subject
GRB 171115A: Swift detection of a burst
Date
2017-11-15T19:05:41Z (7 years ago)
From
David Palmer at LANL <palmer@lanl.gov>
B. Sbarufatti (PSU), D. N. Burrows (PSU), A. Deich (PSU),
J.D. Gropp (PSU), J. A. Kennea (PSU), H. A. Krimm (NSF/USRA),
S. J. LaPorte (PSU), A. Y. Lien (GSFC/UMBC),
F. E. Marshall (NASA/GSFC), K. L. Page (U Leicester),
D. M. Palmer (LANL), M. H. Siegel (PSU) and A. Tohuvavohu (PSU) report
on behalf of the Swift Team:

At 18:51:20 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 171115A (trigger=790053).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 278.413, +9.128 which is 
   RA(J2000) = 18h 33m 39s
   Dec(J2000) = +09d 07' 42"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a complex
structure with a duration of about 50 sec.  The peak count rate
was ~1000 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 18:52:30.0 UT, 69.2 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
fading, uncatalogued X-ray source with an enhanced position: RA, Dec
278.3885, 9.1250 which is equivalent to:
   RA(J2000)  = 18h 33m 33.23s
   Dec(J2000) = +09d 07' 29.9"
with an uncertainty of 2.3 arcseconds (radius, 90% containment). This
location is 87 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 2.97
x 10^21 cm^-2 (Willingale et al. 2013). 

The initial flux in the 2.5 s image was 7.83e-10 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White 
filter  starting 76 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 0.23. 

Burst Advocate for this burst is B. Sbarufatti (bxs60 AT psu.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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