TITLE:   GCN CIRCULAR
NUMBER:  11386
SUBJECT: GRB 101030A: Swift detection of a burst
DATE:    10/10/30 16:13:55 GMT
FROM:    David Palmer at LANL  <palmer@lanl.gov>

A. Melandri (INAF-OAB), S. D. Barthelmy (GSFC), M. M. Chester (PSU),
V. D'Elia (ASDC), J. M. Gelbord (PSU), C. Guidorzi (U Ferrara),
S. T. Holland (CRESST/USRA/GSFC), E. A. Hoversten (PSU),
J. A. Kennea (PSU), H. A. Krimm (CRESST/GSFC/USRA),
R. Margutti (INAF-OAB), F. E. Marshall (NASA/GSFC),
K. L. Page (U Leicester), D. M. Palmer (LANL), M. H. Siegel (PSU) and
E. Troja (NASA/GSFC/ORAU) report on behalf of the Swift Team:

At 15:56:29 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 101030A (trigger=437408).  Swift slewed immediately to the burst. 
The BAT on-board calculated location is 
RA, Dec 166.390, -16.387 which is 
   RA(J2000)  =  11h 05m 34s
   Dec(J2000) = -16d 23' 11"
with an uncertainty of 3 arcmin (radius, 90% containment, including 
systematic uncertainty).  The BAT light curve shows that the burst began
with a bright peak starting at around -70 sec from the trigger, 
followed by a second episode starting at T-10 sec and consisting of two
overlapping peaks with a duration of about 80 sec.  We note that the 
first peak occurred during a pre-planned slew, so the BAT could not 
trigger on it; it is also possible that BAT missed emission from the 
burst before T-100 sec.  The peak count rate was ~2000 counts/sec 
(15-350 keV), at ~0 sec after the trigger. 


The XRT began observing the field at 15:57:35.6 UT, 65.7 seconds after
the BAT trigger. Using promptly downlinked data we find a bright,
fading, uncatalogued X-ray source with an enhanced position: RA, Dec
166.3825, -16.3782 which is equivalent to:
   RA(J2000)  = 11h 05m 31.80s
   Dec(J2000) = -16d 22' 41.5"
with an uncertainty of 2.5 arcseconds (radius, 90% containment). This
location is 40 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 consistent with the Galactic value of 4.24
x 10^20 cm^-2 (Kalberla et al. 2005). 

The initial flux in the 2.5 s image was 2.81e-09 erg cm^-2 s^-1 (0.2-10
keV). 

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 73 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
0.04. 

Burst Advocate for this burst is A. Melandri (andrea.melandri AT brera.inaf.it). 
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.)