TITLE:   GCN CIRCULAR
NUMBER:  17348
SUBJECT: GRB 150123A: Swift-XRT observations
DATE:    15/01/24 10:33:12 GMT
FROM:    Andrea Melandri at INAF-OAB  <andrea.melandri@brera.inaf.it>

A. Melandri, P. D'Avanzo, M.G. Bernardini (INAF-OAB) & P.A. Evans (U. Leicester) report on behalf of the Swift-XRT team:

Swift-XRT has observed the error circle of the MAXI GRB 150123A in a series of observations tiled on the sky. The total exposure time is 3.7 ks spread over 4 fields; the maximum exposure within the sky observed was 1.6 ks. The observations started 9.8 ks after the MAXI trigger. 

Within these data there are 3 objects which are not catalogued in the X-rays.

Source details:

Source 1
RA:  111.36420 = 07h 25m 27.41s (J2000)
Dec:  -9.74880	 = -09d 44' 55.7" (J2000)
Err: 5.9 (radius, 90% confidence)
Exposure time: 814 s
Online products:
http://www.swift.ac.uk/xrt_products/TILED_GRB00038/index_1.php

Source 2
RA:  111.52056 = 07h 26m 4.93s (J2000)
Dec:  -9.65269	 = -09d 39' 09.7" (J2000)
Err: 4.4 (radius, 90% confidence)
Exposure time: 1.3 ks
Online products:
http://www.swift.ac.uk/xrt_products/TILED_GRB00038/index_2.php

Source 3
RA:  111.40659 = 07h 25m 37.58s (J2000)
Dec:  -9.55462	 = -09d 33' 16.6" (J2000)
Err: 5.2 (radius, 90% confidence)
Exposure time: 1.5 ks
Online products:
http://www.swift.ac.uk/xrt_products/TILED_GRB00038/index_3.php


Source #1 is located 3" from an optical source present in the USNO-B1.0 catalogue with a magnitude of R=15.5. Source #2 is located 4" from an optical source present in the USNO-B1.0 catalogue with a magnitude of R=18.0. Source #3 matches the position of the known bright star TYC 5400-1552-1 (R=10.8). 

At the present time we cannot be sure which, if any, of these is the afterglow.

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