TITLE: GCN CIRCULAR NUMBER: 27936 SUBJECT: GRB 200613A: Swift-XRT afterglow detection DATE: 20/06/14 04:46:25 GMT FROM: Kim Page at U.of Leicester J.A. Kennea (PSU), A. Tohuvavohu (U. Toronto), B. Sbarufatti (PSU), J.P. Osborne (U. Leicester), K.L. Page (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 200613A (Ohno et al. GCN Circ. 27931), collecting 4.9 ks of Photon Counting (PC) mode data between T0+43.6 ks and T0+67.6 ks. Seven uncatalogued X-ray sources are detected, of which one ("Source 2") is above the RASS limit, and is therefore likely the GRB afterglow. Using 4079 s of PC mode data and 4 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 = 153.04199, +45.75408 which is equivalent to: RA (J2000): 10h 12m 10.08s Dec(J2000): +45d 45' 14.7" with an uncertainty of 1.4 arcsec (radius, 90% confidence). This position is 5.8 arcmin from the Fermi/LAT position. The light curve can be modelled with a power-law decay with a decay index of alpha=1.6 (+/-0.5). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.89 (+0.14, -0.13). The best-fitting absorption column is 2.3 (+/-0.5) x 10^21 cm^-2, in excess of the Galactic value of 8.4 x 10^19 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.5 x 10^-11 (4.7 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 2.3 (+/-0.5) x 10^21 cm^-2 Galactic foreground: 8.4 x 10^19 cm^-2 Excess significance: 7.5 sigma Photon index: 1.89 (+0.14, -0.13) The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00021003. The results of the full analysis of the XRT observations are available at https://www.swift.ac.uk/ToO_GRBs/00021003. This circular is an official product of the Swift-XRT team.