TITLE: GCN CIRCULAR NUMBER: 27157 SUBJECT: GRB 200219C: Swift-XRT afterglow detection DATE: 20/02/20 20:10:40 GMT FROM: Valerio D'Elia at ASDC D.N. Burrows (PSU), J. D. Gropp (PSU), J.A. Kennea (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), A. Melandri (INAF-OAB), T. Sbarrato (INAF-OAB), P. D'Avanzo (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 200219C (Dirirsa et al. GCN Circ. 27151) in a series of observations tiled on the sky. The total exposure time is 2.4 ks, distributed over 4 tiles; the maximum exposure at a single sky location was 2.4 ks. The data were collected between T0+43.0 ks and T0+56.0 ks, and are entirely in Photon Counting (PC) mode. Two uncatalogued X-ray sources are detected, of which one ("Source 2") is above the RASS limit, and is therefore likely the GRB afterglow. Using 2417 s of PC mode data and 5 UVOT images, we find an enhanced XRT position (using the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue): RA, Dec = 262.50899, +10.53933 which is equivalent to: RA (J2000): 17h 30m 02.16s Dec(J2000): +10d 32' 21.6" with an uncertainty of 2.1 arcsec (radius, 90% confidence). This position is 12.9 arcmin from the Fermi/LAT position. The light curve is consistent with a constant source of mean count rate 1.1e-01 ct/sec. A power-law fit gives an index of 0.9 (+1.4, -1.5). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.1 (+/-0.4). The best-fitting absorption column is 3.2 (+1.6, -1.4) x 10^21 cm^-2, in excess of the Galactic value of 1.2 x 10^21 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.1 x 10^-11 (4.9 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 3.2 (+1.6, -1.4) x 10^21 cm^-2 Galactic foreground: 1.2 x 10^21 cm^-2 Excess significance: 2.4 sigma Photon index: 2.1 (+/-0.4) The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00020973. The results of the full analysis of the tiled XRT observations are available at https://www.swift.ac.uk/xrt_products/TILED_GRB00088. This circular is an official product of the Swift-XRT team.