GCN Circular 12067

B. Sbarufatti (INAF-OAB/IASFPA), J. Cummings (GSFC), M. De Pasquale 
(MSSL) report on behalf of the Swift Team.

We have analyzed 14.5 ks of Photon Counting data for GRB 110604A 
(Barthelmy et al., GCN 12063
Not found
 
 
), observed from 138 ks to 425 ks after the 
Konus-Wind trigger.

We find a single, fading source inside the XRT field of view. Using 2497 
s of XRT Photon Counting mode data and 2 UVOT images, we find an 
astrometrically corrected X-ray position (using the XRT-UVOT alignment 
and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 
270.85885, +18.39961 which is equivalent to:

RA (J2000):   18h 03m 26s.12
Dec(J2000):  +18d 23' 58".6

with an uncertainty of 2.4 arcsec (radius, 90% confidence). This is 9.3 
arcmin away from the initial IPN position. The source was first detected 
at a level of (1.2+/-0.2)E-3 counts/s (equivalent to 5.1E-13 erg cm^-2 
s^-1), 138 ks after the trigger, and has faded to a level of 
(1.4+/-0.6)E-3 counts/s at 421 ks (equivalent to 6.0E-14 erg cm^-2 
s^-1). Another Swift observation is planned for June 14, 2011 in order 
to confirm fading.

No optical source is found within the XRT error circle. Preliminary 
3-sigma upper limits using the UVOT photometric system (Poole et al. 
2008, MNRAS, 383, 627) are:


Filter  T_start (s)   T_end (s)  Exp (s)  mag
white    207930       237252     1399     >22.9
v        208162       237295     516      >19.6
u        207698       240533     2864     >21.5


The magnitudes in the table are not corrected for the Galactic 
extinction due to the reddening of E(B-V) = 0.24 in the direction of the 
burst (Schlegel et al. 1998).

This circular is an official product of the Swift-XRT team.