TITLE:   GCN CIRCULAR
NUMBER:  37981
SUBJECT: GRB 241030B: Swift detection of a burst
DATE:    24/10/30 18:46:07 GMT
FROM:    David Palmer at LANL <palmer@lanl.gov>

N. J. Klingler (GSFC/UMBC/CRESSTII), M. Ferro (INAF-OAB),
J. A. Kennea (PSU), F. E. Marshall (NASA/GSFC),
K. L. Page (U Leicester), D. M. Palmer (LANL), T. M. Parsotan (GSFC),
C. Salvaggio (INAF-OAB), T. Sbarrato (INAF-OAB) and
M. A. Williams (PSU) report on behalf of the Neil Gehrels Swift
Observatory Team:

At 18:34:20 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 241030B (trigger=1263840).  Swift slewed immediately to the burst.
The BAT on-board calculated location is 
RA, Dec 50.788, +34.432 which is 
   RA(J2000) = 03h 23m 09s
   Dec(J2000) = +34d 25' 57"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed a single peak
structure with a duration of about 8 sec.  The peak count rate
was ~2500 counts/sec (15-350 keV), at ~0 sec after the trigger.

The XRT began observing the field at 18:36:58.0 UT, 157.2 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 50.79212, 34.44596 which is equivalent
to:
   RA(J2000)  = 03h 23m 10.11s
   Dec(J2000) = +34d 26' 45.5"
with an uncertainty of 3.7 arcseconds (radius, 90% containment). This
location is 51 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 consistent with the Galactic value of 2.01
x 10^21 cm^-2 (Willingale et al. 2013).

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 160 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.
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
0.203.

Burst Advocate for this burst is N. J. Klingler (noelklin AT umbc.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/)