GCN Circular 36430

S. Laha (GSFC/UMBC), A. D'Ai (INAF-IASFPA),
V. D'Elia (SSDC & INAF-OAR), S. Dichiara (PSU), R. Gupta (NASA/GSFC),
J. A. Kennea (PSU), N. P. M. Kuin (UCL-MSSL), A. Y. Lien (U Tampa),
D. M. Palmer (LANL) and M. H. Siegel (PSU) report on behalf of the
Neil Gehrels Swift Observatory Team:

At 18:06:53 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 240511A (trigger=1227767).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 336.664, +8.514 which is 
   RA(J2000) = 22h 26m 39s
   Dec(J2000) = +08d 30' 49"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve showed multi-peaked
structure with a duration of about 100 sec.  The peak count rate
was ~ 4600 counts/sec (15-350 keV), at ~20 sec after the trigger. 

The XRT began observing the field at 18:08:36.4 UT, 103.2 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
fading, uncatalogued X-ray source located at RA, Dec 336.67568, 8.51315
which is equivalent to:
   RA(J2000)  = 22h 26m 42.16s
   Dec(J2000) = +08d 30' 47.3"
with an uncertainty of 4.2 arcseconds (radius, 90% containment). This
location is 41 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. No
spectrum from the promptly downlinked event data is yet available to
determine the column density. 

The initial flux in the 2.5 s image was 3.70e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 110 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
0.098. 

Burst Advocate for this burst is S. Laha (sib.laha 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/)