[vsnet-grb-info 15499] GRB 140907A: Swift detection of a burst with an optical counterpart

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  16788
SUBJECT: GRB 140907A: Swift detection of a burst with an optical counterpart
DATE:    14/09/07 16:34:45 GMT
FROM:    David Palmer at LANL  <palmer at lanl.gov>

H. A. Krimm (CRESST/GSFC/USRA), V. D'Elia (ASDC), C. Gronwall (PSU),
L. Izzo (URoma/ICRA), K. L. Page (U Leicester), D. M. Palmer (LANL)
and T. N. Ukwatta (LANL) report on behalf of the Swift Team:

At 16:07:08 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 140907A (trigger=611933).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 48.147, +46.595 which is 
   RA(J2000) = 03h 12m 35s
   Dec(J2000) = +46d 35' 42"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a single spiky peak
structure with a duration of about 40 sec.  The peak count rate
was ~3100 counts/sec (15-350 keV), at ~15 sec after the trigger. 

The XRT began observing the field at 16:08:32.3 UT, 83.6 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
fading, uncatalogued X-ray source with an enhanced position: RA, Dec
48.1461, 46.6051 which is equivalent to:
   RA(J2000)  = 03h 12m 35.06s
   Dec(J2000) = +46d 36' 18.2"
with an uncertainty of 2.2 arcseconds (radius, 90% containment). This
location is 36 arcseconds from the BAT onboard position, within the BAT
error circle. This position may be improved as more data are received;
the latest position is available at http://www.swift.ac.uk/sper. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density consistent with the Galactic value of 3.13
x 10^21 cm^-2 (Willingale et al. 2013). 

The initial flux in the 2.5 s image was 5.46e-10 erg cm^-2 s^-1 (0.2-10
keV). 

Automated analysis of the UVOT data products is not available, however
there appears to be a new bright optical source at the XRT position in
the prompt finding chart exposure.  More information will be available
when the full dataset is received. 

Burst Advocate for this burst is H. A. Krimm (hans.krimm 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.)