[vsnet-grb-info 10555] GRB 110428A : Swift-XRT observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  11984
SUBJECT: GRB 110428A : Swift-XRT observations
DATE:    11/04/29 14:46:44 GMT
FROM:    Andrea Melandri at INAF-OAB  <andrea.melandri at brera.inaf.it>

A. Melandri, P. D'Avanzo, R. Margutti (INAF-OAB), B. Sbarufatti (INAF- 
OAB/IASFPA) and M. Stamatikos (OSU/NASA/GSFC) report on behalf of the  
Swift Team:

At 00:47 UT, April 29th, 2011, Swift began a Target of Opportunity  
observation of the Fermi GBM/LAT discovered burst GRB 110428A  
(Vasileiou et al. GCN 11982), ~55.6 ks after the Fermi detection.

In 4.8 ks of Photon Counting mode data, we detect two sources within  
the Fermi-LAT error circle (0.15 deg radius, 68% CL) at the following  
positions:

Source 1:
RA(J2000):   00 21 50.47
Dec(J2000): +64 48 52.4
with an uncertainty of 4.6 arcsec.

Source 2:
RA(J2000):   00 22 22.22
Dec(J2000): +64:50:57.1
with an uncertainty of 7.1 arcsec.

Uncertainty radii are given at 90% containment.

We note that the position of Source 1 is consistent with a known  
ROSAT source (1RXS J002150.5+644850) also present in the DSS. Source  
2 is an uncatalogued object.

The two sources have a count rate of about (1.2e-2 +/- 1.8e-3) and  
(2.9e-3 +/- 9.1e-4) cts/s, respectively. It is not possible to  
determine whether these sources are fading given the current  
statistics. Further Swift-XRT observations of the field are planned.  
We encourage ground-based follow-up observations.

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