GCN Circular 12673
Subject
GRB 111211A: Swift/XRT target of opportunity observation
Date
2011-12-12T22:16:39Z (13 years ago)
From
Binbin Zhang at PSU <buz12@psu.edu>
B.-B. Zhang (PSU) report on behalf of the Swift Team:
Swift began a target of opportunity observation of GRB 111211A on
December 12, 2011 at 15:53 UT, approximately 0.74 days after the burst
was detected by SuperAGILE. Swift data for these observations utilize
Target ID 20192.
We have analysed 2.5 ks of XRT data for the SuperAGILE-detected burst:
GRB 111211A (Lazzarotto et al. et al. GCN Circ. 12666), from 63.5 ks to
66.0 ks after the SuperAGILE trigger. The data are entirely in Photon
Counting (PC) mode. An X-ray source is detected within the SuperAGILE
error circle. Using 2512 s of PC mode data and 3 UVOT images, we find
an enhanced XRT position (using the XRT-UVOT alignment and matching
UVOT field sources to the USNO-B1 catalogue): RA, Dec = 153.09040,
+11.20789 which is equivalent to:
RA (J2000): 10h 12m 21.70s
Dec(J2000): +11d 12' 28.4"
with an uncertainty of 1.8 arcsec (radius, 90% confidence). This
position is 93 arcsec from the SuperAGILE position and 1.6 arcsec from
the GROND afterglow candidate position (Kann et al. GCN Circ. 12668),
which confirms it is the X-ray afterglow of GRB 111211A. The light
curve is consistent with a constant source of mean count rate 1.3e-01
ct/sec. A power-law fit gives an index of -1.309 (+4.183, -0.020).
A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.02 (+0.18, -0.26). The
best-fitting absorption column is 1.3 (+0.7, -0.6) x 10^21 cm^-2, in
excess of the Galactic value of 3.4 x 10^20 cm^-2 (Kalberla et al.
2005). The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum is 3.7 x 10^-11 (4.9 x 10^-11) erg
cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 1.3 (+0.7, -0.6) x 10^21 cm^-2
Galactic foreground: 3.4 x 10^20 cm^-2
Excess significance: 2.5 sigma
Photon index: 2.02 (+0.18, -0.26)
The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00020192.
This circular is an official product of the Swift-XRT team.