TITLE:   GCN CIRCULAR
NUMBER:  9668
SUBJECT: GRB 090715B: Swift detection of a burst with a possible optical counterpart
DATE:    09/07/15 21:34:31 GMT
FROM:    Loredana Vetere at PSU  <vetere@astro.psu.edu>

L. Vetere (PSU), A. P. Beardmore (U Leicester),
N. Gehrels (NASA/GSFC), C. Gronwall (PSU),
S. T. Holland (CRESST/USRA/GSFC), F. E. Marshall (NASA/GSFC),
P. T. O'Brien (U Leicester), J. P. Osborne (U Leicester),
C. Pagani (PSU), J. L. Racusin (PSU), B. Sbarufatti (INAF-IASFPA),
M. H. Siegel (PSU), M. Stamatikos (NASA/ORAU) and M. A. Stark (PSU)
report on behalf of the Swift Team:

At 21:03:14 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 090715B (trigger=357512).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 251.344, +44.827 which is 
   RA(J2000) = 16h 45m 23s
   Dec(J2000) = +44d 49' 36"
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 100 sec.  The peak count rate
was ~8000 counts/sec (15-350 keV), at ~6 sec after the trigger. 

The XRT began observing the field at 21:04:00.9 UT, 46.2 seconds after
the BAT trigger. XRT found a bright, uncatalogued X-ray source located
at RA, Dec 251.3405, +44.8377 which is equivalent to:
   RA(J2000)  = 16h 45m 21.71s
   Dec(J2000) = +44d 50' 15.7"
with an uncertainty of 4.9 arcseconds (radius, 90% containment). This
location is 39 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. 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 53 seconds after the BAT trigger. There is a weak source in
2.7'x2.7' sub-image near the edge of the XRT error circle at the position of
  RA(J2000) = 16:45:21.62
  Dec(J2000) = +44:50:21.3
The estimated white magnitude 20.5 with an estimated error of 0.5 mag. 
No correction has been made for the expected extinction corresponding 
to E(B-V) of 0.01. 

Swift autonomous slewing to new GRBs was enabled just prior to this
burst.  It was disabled previously due to an anomaly with the
on-board solid state recorder.  That problem is now resolved. 

Burst Advocate for this burst is L. Vetere (vetere AT astro.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.)