TITLE: GCN CIRCULAR NUMBER: 23941 SUBJECT: GRB 190306A: Swift-XRT observations DATE: 19/03/07 17:38:55 GMT FROM: Valerio D'Elia at ASDC D.N. Burrows (PSU), A. Tohuvavohu (PSU), S. J. LaPorte (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), P. D'Avanzo (INAF-OAB), V. D'Elia (ASDC), A. D'Ai (INAF-IASFPA) 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 190306A (Shidatsu et al. GCN Circ. 23937) in a series of observations tiled on the sky. The total exposure time is 1.2 ks, distributed over 7 tiles; the maximum exposure at a single sky location was 379 s. The data were collected between T0+24.2 ks and T0+25.6 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 ~0.05 to ~0.15 ct s^-1, corresponding to a 0.3-10 keV observed flux of 1.8e-12 to 6.1e-12 erg cm^-2 s^-1 (assuming a typical GRB spectrum). A previously-catalogued X-ray source has been detected, however because it is a catalogued object it is 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_GRB00078. This circular is an official product of the Swift-XRT team.