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GCN Circular 12631

Subject
GRB 111208A: Swift XRT/UVOT observations
Date
2011-12-08T22:00:03Z (12 years ago)
From
Erik Hoversten at Swift/Penn State <hoversten@astro.psu.edu>
C. A. Wolf (PSU), E. A. Hoversten (PSU), and T. Sakamoto (GSFC/UMBC)  
report on behalf of the Swift team:

We have analyzed 2.85 ks of XRT data for the BAT ground-detected  
burst: GRB 111208A (Sakamoto et. al. GCN Circ. 12628), from 24.3 ks to  
34.9 ks after the burst. The data are entirely in Photon Counting (PC)  
mode. An uncataloged X-ray source is detected within the BAT error  
circle and is potentially the afterglow of GRB 111208A. The refined  
XRT position is RA, Dec = 290.2251, +40.6766 which is equivalent to:

RA (J2000); 19 20 54.0
Dec(J2000): +40 40 35.8

with an uncertainty of 4.1 arcsec (radius, 90% confidence). This  
position is 39.7 arcsec from the BAT position, within the BAT error  
circle. This position may be improved as more data are received. We  
cannot determine whether the source is fading at the present time.
The Swift/UVOT began settled observations of the field of GRB 111208A  
24.3 ks after the BAT trigger. No optical afterglow consistent with  
the XRT position is detected in the initial UVOT exposures.   
Preliminary 3-sigma upper limits using the UVOT photometric system  
(Poole et al. 2008, MNRAS, 383, 627) for the initial exposures are:

Filter         T_start(ks)   T_stop(ks)      Exp(s)         Mag
white             24.3          34.9          2100         >22.0
The magnitude in the table is not corrected for the Galactic  
extinction due to the reddening of E(B-V) = 0.12 in the direction of  
the burst (Schlegel et al. 1998).  We note that this is a crowded  
field and that there is a source a few arcseconds outside the XRT  
error circle.  However, this source is clearly visible in archival  
optical imaging.
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