[vsnet-grb-info 18439] GRB 160905A: Swift detection of a burst with an optical counterpart

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  19887
SUBJECT: GRB 160905A: Swift detection of a burst with an optical counterpart
DATE:    16/09/05 11:31:37 GMT
FROM:    David Palmer at LANL  <palmer at lanl.gov>

P. D'Avanzo (INAF-OAB), A. P. Beardmore (U Leicester),
A. A. Breeveld (UCL-MSSL), D. N. Burrows (PSU),
P.A. Evans (U Leicester), J. A. Kennea (PSU),
N. P. M. Kuin (UCL-MSSL), F. E. Marshall (NASA/GSFC),
P. T. O'Brien (U Leicester), D. M. Palmer (LANL) and
B. Sbarufatti (INAF-OAB/PSU) report on behalf of the Swift Team:

At 11:18:58 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 160905A (trigger=711084).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 162.237, -50.800 which is 
   RA(J2000) = 10h 48m 57s
   Dec(J2000) = -50d 47' 59"
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 ~13000 counts/sec (15-350 keV), at ~18 sec after the trigger. 

The XRT began observing the field at 11:19:56.0 UT, 57.7 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 162.2448, -50.8014 which is equivalent to:
   RA(J2000)  = +10h 48m 58.75s
   Dec(J2000) = -50d 48' 05.0"
with an uncertainty of 4.8 arcseconds (radius, 90% containment). This
location is 18 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 6.05e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 66 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	10:48:59.18 = 162.24658
  DEC(J2000) = -50:48:04.3  = -50.80120
with a 90%-confidence error radius of about 0.61 arc sec. This position is 4.1
arc sec. from the center of the XRT error circle. The estimated magnitude is
15.88 with a 1-sigma error of about  0.14. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.46. 

Burst Advocate for this burst is P. D'Avanzo (paolo.davanzo AT brera.inaf.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.)