TITLE:   GCN CIRCULAR
NUMBER:  34655
SUBJECT: GRB 230911C: Swift detection of a burst
DATE:    23/09/11 09:11:10 GMT
FROM:    K.L. Page at U Leicester <klp5@leicester.ac.uk>


E. Sonbas (Adiyaman Univ.), R. Brivio (INAF-OAB), S. Dichiara (PSU),
M. Ferro (INAF-OAB), J.D. Gropp (PSU), A. Y. Lien (U Tampa),
A. Melandri (INAF-OAR), K. L. Page (U Leicester), D. M. Palmer (LANL),
T. Sakamoto (AGU), C. Salvaggio (INAF-OAB) and T. Sbarrato (INAF-OAB)
report on behalf of the Neil Gehrels Swift Observatory Team:

At 08:47:25 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 230911C (trigger=1191188).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 226.782, -41.334 which is 
   RA(J2000) = 15h 07m 08s
   Dec(J2000) = -41d 20' 01"
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 10 sec.  The peak count rate
was ~700 counts/sec (15-350 keV), at ~3 sec after the trigger. 

The XRT began observing the field at 08:49:24.4 UT, 119.0 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source located at RA, Dec 226.79804, -41.32973 which is
equivalent to:
   RA(J2000)  = 15h 07m 11.53s
   Dec(J2000) = -41d 19' 47.0"
with an uncertainty of 4.2 arcseconds (radius, 90% containment). This
location is 46 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 (9.36 x
10^20 cm^-2, Willingale et al. 2013), with an excess column of 4
(+3.90/-3.22) x 10^21 cm^-2 (90% confidence). 

Processed UVOT data were not available at low latency, with the images
affected by the attitude issues reported in GCN Circ. 34633. 

Burst Advocate for this burst is E. Sonbas (edasonbas AT yahoo.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/)