[vsnet-grb-info 20671] GRB 180613A: Swift detection of a burst

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  22769
SUBJECT: GRB 180613A: Swift detection of a burst
DATE:    18/06/13 15:53:16 GMT
FROM:    Jamie A. Kennea at PSU/Swift-XRT  <kennea at swift.psu.edu>

A. Tohuvavohu (PSU), S. D. Barthelmy (GSFC),
A. P. Beardmore (U Leicester), J.D. Gropp (PSU), J. A. Kennea (PSU),
A. Y. Lien (GSFC/UMBC), F. E. Marshall (NASA/GSFC),
K. L. Page (U Leicester), D. M. Palmer (LANL), M. H. Siegel (PSU) and
T. N. Ukwatta (LANL) report on behalf of the Neil Gehrels Swift
Observatory Team:

At 15:36:18 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 180613A (trigger=840853).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 211.562, -43.076 which is 
   RA(J2000) = 14h 06m 15s
   Dec(J2000) = -43d 04' 31"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  As is usual with an image trigger, the available
BAT light curve shows no significant structure. 

The XRT began observing the field at 15:38:47.7 UT, 148.9 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
fading, uncatalogued X-ray source located at RA, Dec 211.52004,
-43.07158 which is equivalent to:
   RA(J2000)  = 14h 06m 04.81s
   Dec(J2000) = -43d 04' 17.7"
with an uncertainty of 3.7 arcseconds (radius, 90% containment). This
location is 111 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 (6.50 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 4.5
(+3.67/-3.01) x 10^21 cm^-2 (90% confidence). 

The initial flux in the 2.5 s image was 5.63e-10 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 250 seconds with the U filter starting
154 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 19.2 mag. The
8'x8' region for the list of sources generated on-board covers 100% of the XRT
error circle. The list of sources is typically complete to about 18.0 mag. No
correction has been made for the expected extinction corresponding to E(B-V) of
0.09. 

Burst Advocate for this burst is A. Tohuvavohu (aaronb AT swift.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.)