[vsnet-grb-info 13402] GRB 130603B: Swift detection of a bright short burst

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  14735
SUBJECT: GRB 130603B: Swift detection of a bright short burst
DATE:    13/06/03 16:15:25 GMT
FROM:    David Palmer at LANL  <palmer at lanl.gov>

A. Melandri (INAF-OAB), W. H. Baumgartner (GSFC/UMBC),
D. N. Burrows (PSU), J. R. Cummings (NASA/UMBC),
N. Gehrels (NASA/GSFC), C. Gronwall (PSU), K. L. Page (U Leicester),
D. M. Palmer (LANL), R. L. C. Starling (U Leicester) and
T. N. Ukwatta (MSU) report on behalf of the Swift Team:

At 15:49:14 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 130603B (trigger=557310).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 172.209, +17.045 which is 
   RA(J2000) = 11h 28m 50s
   Dec(J2000) = +17d 02' 42"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a single spike
structure with a duration of about 0.4 sec.  The peak count rate
was 60000 counts/sec (15-350 keV), at ~0 sec after the trigger. 

The XRT began observing the field at 15:50:12.8 UT, 59.0 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source with an enhanced position: RA, Dec 172.2006, 17.0719 which
is equivalent to:
   RA(J2000)  = 11h 28m 48.16s
   Dec(J2000) = +17d 04' 18.8"
with an uncertainty of 2.7 arcseconds (radius, 90% containment). This
location is 101 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 in excess of the Galactic value (1.93 x
10^20 cm^-2, Kalberla et al. 2005), with an excess column of 6.8
(+4.00/-3.31) x 10^21 cm^-2 (90% confidence). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 62 seconds after the BAT trigger. No credible afterglow candidate has
been found in the initial data products. The 2.7'x2.7' sub-image covers 25% of
the BAT error circle. The typical 3-sigma upper limit has been about 19.6 mag. 
The 8'x8' region for the list of sources generated on-board covers 100% of the
BAT error circle. The list of sources is typically complete to about 18 mag. No
correction has been made for the expected extinction corresponding to E(B-V) of
0.02. 

The Swift star trackers were not locked at the time of the
burst, so there may be some additional error in the position. 
However the spike in the rates and the image detection is
unambiguously real. 

We note that this bright short hard GRB is near (12 arcminutes) 
the location of the nearby galaxy NGC 3691.  At z=0.003566, this
corresponds to a nominal projected distance of about 50 kpc. 

Burst Advocate for this burst is A. Melandri (andrea.melandri 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.)