[vsnet-grb-info 19494] GRB 170607A: Swift detection of a burst with a bright optical counterpart

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  21214
SUBJECT: GRB 170607A: Swift detection of a burst with a bright optical counterpart
DATE:    17/06/07 23:32:47 GMT
FROM:    David Palmer at LANL  <palmer at lanl.gov>

A. D'Ai (INAF-IASFPA), D. N. Burrows (PSU), A. Cholden-Brown (PSU),
V. D'Elia (ASDC), J. A. Kennea (PSU), N. P. M. Kuin (UCL-MSSL),
F. E. Marshall (NASA/GSFC), D. M. Palmer (LANL),
B. Sbarufatti (INAF-OAB/PSU) and M. H. Siegel (PSU) report on behalf
of the Swift Team:

At 23:21:33 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 170607A (trigger=756284).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 7.343, +9.238 which is 
   RA(J2000) = 00h 29m 22s
   Dec(J2000) = +09d 14' 16"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a single FRED
structure with a duration of about 40 sec.  The peak count rate
was ~4000 counts/sec (15-350 keV), at ~1 sec after the trigger. 

The XRT began observing the field at 23:22:47.1 UT, 73.4 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 7.3655, 9.2425 which is equivalent to:
   RA(J2000)  = +00h 29m 27.72s
   Dec(J2000) = +09d 14' 33.0"
with an uncertainty of 4.8 arcseconds (radius, 90% containment). This
location is 81 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 5.32e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 83 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	00:29:27.80 =	7.36582
  DEC(J2000) = +09:14:36.2  =	9.24339
with a 90%-confidence error radius of about 0.61 arc sec. This position is 3.4
arc sec. from the center of the XRT error circle. The estimated magnitude is
15.90 with a 1-sigma error of about  0.14. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.04. 

Burst Advocate for this burst is A. D'Ai (antonino.dai AT ifc.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.)