TITLE:   GCN CIRCULAR
NUMBER:  37722
SUBJECT: GRB 241006A: Swift detection of a burst
DATE:    24/10/06 22:07:26 GMT
FROM:    K.L. Page at U Leicester <klp5@leicester.ac.uk>

R. Gupta (NASA GSFC), M. J. Moss (GSFC), K. L. Page (U Leicester),
D. M. Palmer (LANL) and B. Sbarufatti (INAF-OAB) report on behalf of
the Neil Gehrels Swift Observatory Team:

At 21:51:58 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 241006A (trigger=1258721).  Swift slewed immediately to the burst.
The BAT on-board calculated location is 
RA, Dec 304.794, -40.796 which is 
   RA(J2000) = 20h 19m 11s
   Dec(J2000) = -40d 47' 44"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a complex
structure with a duration of about 30 sec.  The peak count rate
was ~700 counts/sec (15-350 keV), at ~-1 sec after the trigger.

The XRT began observing the field at 21:54:23.5 UT, 145.3 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
uncatalogued X-ray source with an enhanced position: RA, Dec 304.74258,
-40.80514 which is equivalent to:
   RA(J2000)  = 20h 18m 58.22s
   Dec(J2000) = -40d 48' 18.5"
with an uncertainty of 1.9 arcseconds (radius, 90% containment). This
location is 143 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
https://www.swift.ac.uk/sper.  We cannot determine whether the source
is fading at the present time. 

A power-law fit to a spectrum formed from promptly downlinked event
data gives a column density in excess of the Galactic value (4.92 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 3.5
(+3.24/-2.77) x 10^21 cm^-2 (90% confidence). 

The initial flux in the 2.5 s image was 4.75e-10 erg cm^-2 s^-1 (0.2-10
keV).

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 349 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 none of
the XRT error circle. 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 mag. No correction has been made for the expected
extinction corresponding to E(B-V) of 0.065.

Burst Advocate for this burst is R. Gupta (rahulbhu.c157 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/)