TITLE:   GCN CIRCULAR
NUMBER:  17904
SUBJECT: GRB 150607A: Swift detection of a burst with an optical counterpart
DATE:    15/06/07 08:10:50 GMT
FROM:    David Palmer at LANL  <palmer@lanl.gov>

V. D'Elia (ASDC), L. Izzo (URoma/ICRA), J. A. Kennea (PSU),
K. L. Page (U Leicester), D. M. Palmer (LANL) and M. H. Siegel (PSU)
report on behalf of the Swift Team:

At 07:55:09 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 150607A (trigger=642620).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 140.024, +68.442 which is 
   RA(J2000) = 09h 20m 06s
   Dec(J2000) = +68d 26' 33"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a multiply-peaked
structure with a duration of about 50 sec.  The peak count rate
was ~3000 counts/sec (15-350 keV), at ~8 sec after the trigger. 

The XRT began observing the field at 07:57:20.5 UT, 130.9 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 139.9916, 68.4368 which is equivalent to:
   RA(J2000)  = +09h 19m 57.98s
   Dec(J2000) = +68d 26' 12.5"
with an uncertainty of 6.5 arcseconds (radius, 90% containment). This
location is 46 arcseconds from the BAT onboard position, within the BAT
error circle. 

The initial flux in the 2.5 s image was 4.64e-10 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 136 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
  RA(J2000)  =	09:19:57.18 = 139.98825
  DEC(J2000) = +68:26:10.2  =  68.43618
with a 90%-confidence error radius of about 0.75 arc sec. This position is 5.0
arc sec. from the center of the XRT error circle. The estimated magnitude is
18.06 with a 1-sigma error of about  0.15. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.06. 

Burst Advocate for this burst is V. D'Elia (delia AT asdc.asi.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.)