TITLE: GCN CIRCULAR NUMBER: 18795 SUBJECT: GRB 160101A: Swift-XRT afterglow detection DATE: 16/01/01 15:30:06 GMT FROM: Valerio D'Elia at ASDC L. Izzo (URoma/ICRA), V. D'Elia (ASDC), P. D'Avanzo (INAF-OAB), T.G.R. Roegiers (PSU), L.M. McCauley (PSU), J.A. Kennea (PSU), A.P. Beardmore (U. Leicester), S.L. Gibson (U. Leicester), 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 160101A (Itoh et al. GCN Circ. 18793) in a series of observations tiled on the sky. The total exposure time is 1.7 ks, distributed over 7 tiles; the maximum exposure at a single sky location was 512 s. The data were collected between T0+13.2 ks and T0+19.6 ks, and are entirely in Photon Counting (PC) mode. An uncatalogued X-ray source is detected and is above the RASS limit, and is therefore likely the GRB afterglow. The position of this source is RA, Dec=219.6506, -13.8154 which is equivalent to: RA (J2000): 14:38:36.14 Dec(J2000): -13:48:55.5 with an uncertainty of 3.7 arcsec (radius, 90% confidence). This position is 4.8 arcmin from the MAXI position. The source has a mean count rate of 3.9e-01 ct/sec; we cannot determine at the present time whether it is fading. A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.5 (+0.5, -0.3). The best-fitting absorption column is 1.20 (+2.17, -0.29) x 10^21 cm^-2, consistent with the Galactic value of 9.1 x 10^20 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 4.6 x 10^-11 (5.1 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 1.20 (+2.17, -0.29) x 10^21 cm^-2 Galactic foreground: 9.1 x 10^20 cm^-2 Excess significance: <1.6 sigma Photon index: 1.5 (+0.5, -0.3) The results of the XRT-team automatic analysis of the likely afterglow are at http://www.swift.ac.uk/xrt_products/TILED_GRB00051/index_1.php. The results of the full analysis of the tiled XRT observations are available at http://www.swift.ac.uk/xrt_products/TILED_GRB00051. This circular is an official product of the Swift-XRT team.