TITLE:   GCN CIRCULAR
NUMBER:  17786
SUBJECT: GRB 150428C: Swift-XRT observations
DATE:    15/04/29 13:06:40 GMT
FROM:    Kim Page at U.of Leicester  <klp5@leicester.ac.uk>

K.L. Page and P.A. Evans (U. Leicester) report on behalf of the Swift-XRT
team:

Swift-XRT has performed follow-up observations of the MAXI-detected
burst GRB 150428C (Honda et al. GCN Circ. 17772) in a series of
observations tiled on the sky. The total exposure time is 2.1 ks,
distributed over 7 tiles; the maximum exposure at a single sky location
was 819 s. The data were collected between T0+16.2 ks and T0+28.9 ks,
and are entirely in Photon Counting (PC) mode.

No real uncatalogued sources have been detected. Although a
low-significance source was reported by the automatic software, we believe
this is an artifact caused by high background emission. In addition, a
previously-catalogued X-ray source has been detected, however because it
is a catalogued object it is unlikely to be the afterglow.

The 3-sigma upper limit in the field ranges from ~0.01 to ~0.05 ct s^-1,
corresponding to a 0.3-10 keV observed flux of 4e-13 to 2e-12 erg cm^-2
s^-1 (assuming a typical GRB spectrum).

The results of the XRT-team automatic analysis of the XRT observations,
including a position-specific upper limit calculator, are available at
http://www.swift.ac.uk/xrt_products/TILED_GRB00043/