TITLE: GCN CIRCULAR NUMBER: 18030 SUBJECT: GRB 150716A: Swift-XRT refined Analysis DATE: 15/07/17 07:19:04 GMT FROM: Phil Evans at U of Leicester B. Sbarufatti (INAF-OAB/PSU), D.N. Burrows (PSU), T.G.R. Roegiers (PSU), A.P. Beardmore (U. Leicester), P.A. Evans (U. Leicester), B.P. Gompertz (U. Leicester), A. Maselli (INAF-IASFPA), A. Melandri (INAF-OAB), P. D'Avanzo (INAF-OAB) and D. Kocevski report on behalf of the Swift-XRT team: We have analysed 3.6 ks of XRT data for GRB 150716A (Kocevski et al. GCN Circ. 18027), from 66 s to 22.7 ks after the BAT trigger. The data comprise 126 s in Windowed Timing (WT) mode (the first 11 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode. The refined XRT position is RA, Dec = 278.4879, -12.9802 which is equivalent to: RA (J2000): 18 33 57.10 Dec(J2000): -12 58 48.9 with an uncertainty of 4.1 arcsec (radius, 90% confidence). The light curve can be modelled with a power-law decay with a decay index of alpha=1.67 (+0.08, -0.06). A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 2.67 (+0.25, -0.23). The best-fitting absorption column is 1.35 (+0.24, -0.22) x 10^22 cm^-2, in excess of the Galactic value of 7.0 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 3.6 x 10^-11 (1.4 x 10^-10) erg cm^-2 count^-1. A summary of the WT-mode spectrum is thus: Total column: 1.35 (+0.24, -0.22) x 10^22 cm^-2 Galactic foreground: 7.0 x 10^21 cm^-2 Excess significance: 4.8 sigma Photon index: 2.67 (+0.25, -0.23) If the light curve continues to decay with a power-law decay index of 1.67, the count rate at T+24 hours will be 2.4 x 10^-4 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 8.8 x 10^-15 (3.5 x 10^-14) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00649157. This circular is an official product of the Swift-XRT team.