[vsnet-grb-info 13448] GRB 130606A: Swift detection of a burst

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  14781
SUBJECT: GRB 130606A: Swift detection of a burst
DATE:    13/06/06 21:25:59 GMT
FROM:    David Palmer at LANL  <palmer at lanl.gov>

T. N. Ukwatta (MSU), S. D. Barthelmy (GSFC), N. Gehrels (NASA/GSFC),
H. A. Krimm (CRESST/GSFC/USRA), D. Malesani (DARK/NBI),
F. E. Marshall (NASA/GSFC), A. Maselli (INAF-IASFPA),
A. Melandri (INAF-OAB), D. M. Palmer (LANL) and
M. Stamatikos (OSU/NASA/GSFC) report on behalf of the Swift Team:

At 21:04:39 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 130606A (trigger=557589).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 249.403, +29.791 which is 
   RA(J2000) = 16h 37m 37s
   Dec(J2000) = +29d 47' 27"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a double-peaked
structure.  The initial peak is about 10 sec long from T-5 to T+5 sec. 
Then at T+150 sec, there is a second, brighter peak of about 20 sec
duration. The peak count rate was ~2300 counts/sec (15-350 keV), 
at ~155 sec after the trigger. 

The XRT began observing the field at 21:05:51.4 UT, 72.4 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
fading, uncatalogued X-ray source located at RA, Dec 249.39916,
29.79428 which is equivalent to:
   RA(J2000)  = 16h 37m 35.80s
   Dec(J2000) = +29d 47' 39.4"
with an uncertainty of 3.6 arcseconds (radius, 90% containment). This
location is 16 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 (1.98 x
10^20 cm^-2, Kalberla et al. 2005), with an excess column of 3.3
(+1.76/-1.58) x 10^21 cm^-2 (90% confidence). 

The initial flux in the 2.5 s image was 1.64e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 80 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 
100% of the XRT error circle. The typical 3-sigma upper limit has been 
about 19.6 mag, but the trailed images will reduce the sensitivity slightly. 
No correction has been made for the expected extinction corresponding 
to E(B-V) of 0.02. 

The UVOT data shows stars trailing by about 10 arcseconds, which
may indicate pointing instability at this level.  Therefore
this uncertainty should be added to the nominal XRT location
for follow-up searches.  A refined aspect solution will be
generated from the full downlinked data. 

Burst Advocate for this burst is T. N. Ukwatta (tilan.ukwatta AT gmail.com). 
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.)