TITLE: GCN CIRCULAR NUMBER: 19655 SUBJECT: GRB 160703A: Swift-XRT afterglow detection DATE: 16/07/05 08:40:09 GMT FROM: Valerio D'Elia at ASDC V. D'Elia (INAF-OAR), L. Izzo (IAA-CSIC), D. Malesani (DARK/NBI), E. Troja (GSFC), B. Sbarufatti (INAF-OAB/PSU), D.N. Burrows (PSU), T.G.R. Roegiers (PSU), B. Mingo (U. Leicester), A.P. Beardmore (U. Leicester), A. Maselli (INAF-IASFPA), A. Melandri (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 Swift/BAT-detected burst GRB 160703A (Lien et al. GCN Circ. 19648), collecting 5.0 ks of Photon Counting (PC) mode data between T0+107.8 ks and T0+120.4 ks. An uncatalogued X-ray source is detected within the 3-sigma Swift/BAT error region and is above the RASS limit, and is therefore likely the GRB afterglow. The position of this source is RA, Dec=287.4168, +36.9175 which is equivalent to: RA (J2000): 19:09:40.04 Dec(J2000): +36:55:03.0 with an uncertainty of 3.9 arcsec (radius, 90% confidence). This position is 92 arcsec from the Swift/BAT position and 5.1 arcsec from the optical transient reported by Tachibana et al. (GCN Circ. 19652). The light curve is consistent with a constant source of mean count rate 1.7e-02 ct/sec. A power-law fit gives an index of 2.92 (+0.03, -3.89). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.9 (+0.7, -0.5). The best-fitting absorption column is 3.0 (+3.9, -1.5) x 10^21 cm^-2, consistent with the Galactic value of 1.5 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 3.9 x 10^-11 (5.4 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 3.0 (+3.9, -1.5) x 10^21 cm^-2 Galactic foreground: 1.5 x 10^21 cm^-2 Excess significance: <1.6 sigma Photon index: 1.9 (+0.7, -0.5) The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00702699. The results of the full analysis of the XRT observations are available at http://www.swift.ac.uk/ToO_GRBs/00702699. This circular is an official product of the Swift-XRT team.