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GCN Circular 11370

Subject
GRB 101024A: Swift detection of a burst with an optical afterglow
Date
2010-10-24T12:03:25Z (14 years ago)
From
Phil Evans at U of Leicester <pae9@star.le.ac.uk>
M. De Pasquale (UCL-MSSL), A. P. Beardmore (U Leicester),
P. A. Evans (U Leicester), N. Gehrels (NASA/GSFC),
S. T. Holland (CRESST/USRA/GSFC), P. T. O'Brien (U Leicester),
C. Pagani (U Leicester), C. J. Saxton (UCL-MSSL),
B. Sbarufatti (INAF-OAB/IASFPA), M. H. Siegel (PSU),
M. Stamatikos (OSU/NASA/GSFC) and R. L. C. Starling (U Leicester)
report on behalf of the Swift Team:

At 11:39:29.82 UT, the Swift Burst Alert Telescope (BAT) triggered and
located GRB 101024A (trigger=437016).  Swift slewed immediately to the burst.
The BAT on-board calculated location is
RA, Dec 66.475, -77.248 which is
    RA(J2000) = 04h 25m 54s
    Dec(J2000) = -77d 14' 50"
with an uncertainty of 3 arcmin (radius, 90% containment, including
systematic uncertainty). The lightcurve shows 4 distinct peaks, with the
brightest peaking at T0+10s. Duration was about 23s.

The XRT began observing the field at 11:40:46.8 UT, 77.0 seconds after
the BAT trigger. Using promptly downlinked data we find an uncatalogued
X-ray source with an enhanced position: RA, Dec 66.5064, -77.2648 which
is equivalent to:
    RA(J2000)  = 04h 26m 1.54s
    Dec(J2000) = -77d 15' 53.2"
with an uncertainty of 2.1 arcseconds (radius, 90% containment). This
location is 66 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 in excess of the Galactic value (6.52 x
10^20 cm^-2, Kalberla et al. 2005), with an excess column of 2.2
(+1.39/-1.27) x 10^21 cm^-2 (90% confidence).

UVOT took a finding chart exposure of 150 seconds with the White filter
starting 81 seconds after the BAT trigger. There is a candidate afterglow in
the rapidly available 2.7'x2.7' sub-image at
   RA(J2000)  =	04:26:01.73 =  66.50719
   DEC(J2000) = -77:15:55.9  = -77.26552
with a 90%-confidence error radius of about 0.64 arc sec. This position is 2.1
arc sec. from the center of the XRT error circle. The estimated magnitude is
19.38 with a 1-sigma error of about  0.15. No correction has been made for the
expected extinction corresponding to E(B-V) of 0.09.

Burst Advocate for this burst is M. De Pasquale (mdp@mssl.ucl.ac.uk).
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.)
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