GCN Circular 20830

V. D'Elia (ASDC), A. D'Ai (INAF-IASFPA), B. Sbarufatti (INAF-OAB/PSU),
D.N. Burrows (PSU), A. Cholden-Brown (PSU), J.P. Osborne (U.
Leicester), K.L. Page (U. Leicester), B. Mingo (U. Leicester), A.
Melandri (INAF-OAB) and P.A. Evans (U. Leicester) report on behalf of
the Swift-XRT team:

Swift-XRT has performed follow-up observations of the
Fermi/LAT-detected burst GRB 170306B in a series of observations tiled
on the sky. The total exposure time is 4.5 ks, distributed over 8
tiles; the maximum exposure at a single sky location was 1.4 ks. The
data were collected between T0+17.4 ks and T0+29.9 ks, and are entirely
in Photon Counting (PC) mode. 

No uncatalogued X-ray sources have been detected. The 3-sigma upper
limit in the field (not including the regions where the tiles overlap)
ranges from ~0.007 to ~0.021 ct s^-1, corresponding to a 0.3-10 keV
observed flux of 2.9e-13 to 8.5e-13 erg cm^-2 s^-1 (assuming a typical
GRB spectrum).

Four previously-catalogued X-ray sources have been detected, however
their status as catalogued objects makes them unlikely to be the
afterglow.

The results of the XRT-team automatic analysis of the tiled XRT
observations, including a position-specific upper limit calculator, are
available at http://www.swift.ac.uk/xrt_products/TILED_GRB00065.

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