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GCN Circular 20064

Subject
GRB 161017A: Swift detection of a burst with a bright optical afterglow
Date
2016-10-17T18:04:12Z (7 years ago)
From
David Palmer at LANL <palmer@lanl.gov>
E. Troja (NASA/GSFC/UMCP), D. N. Burrows (PSU),
P. D'Avanzo (INAF-OAB), N. Gehrels (NASA/GSFC), J. A. Kennea (PSU),
N. P. M. Kuin (UCL-MSSL), A. Y. Lien (GSFC/UMBC),
C. B. Markwardt (NASA/GSFC), F. E. Marshall (NASA/GSFC),
A. Melandri (INAF-OAB), K. L. Page (U Leicester), D. M. Palmer (LANL)
and T. N. Ukwatta (LANL) report on behalf of the Swift Team:

At 17:51:51 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 161017A (trigger=718023).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 142.765, +43.142 which is 
   RA(J2000) = 09h 31m 04s
   Dec(J2000) = +43d 08' 30"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a multi-peaked
structure with a duration of about 160 sec.  The peak count rate
was ~2100 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 17:52:48.8 UT, 57.7 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 142.7681, 43.1300 which is equivalent to:
   RA(J2000)  = +09h 31m 4.34s
   Dec(J2000) = +43d 07' 48.0"
with an uncertainty of 4.9 arcseconds (radius, 90% containment). This
location is 43 arcseconds from the BAT onboard position, within the BAT
error circle. No event data are yet available to determine the column
density using X-ray spectroscopy. 

The initial flux in the 2.5 s image was 3.24e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of nominal 150.000 seconds with the White
filter starting 67 seconds after the BAT trigger. There is a candidate
afterglow in the list of sources generated on-board at
  RA(J2000)  =	09:31:04.58 = 142.76910
  DEC(J2000) = +43:07:36.3  =  43.12675
with a 90%-confidence error radius of about 1.10 arc sec. This position is 12.0
arc sec. from the center of the XRT error circle. The estimated magnitude is
13.86. No correction has been made for the expected extinction corresponding to
E(B-V) of 0.02. 

Burst Advocate for this burst is E. Troja (eleonora.troja AT nasa.gov). 
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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