TITLE: GCN CIRCULAR NUMBER: 19868 SUBJECT: GRB 160826A: Swift-XRT refined Analysis DATE: 16/08/26 15:36:20 GMT FROM: Phil Evans at U of Leicester P.A. Evans (U. Leicester), A. D'Ai (INAF-IASFPA), A. Maselli (INAF-IASFPA), A. Melandri (INAF-OAB), J.A. Kennea (PSU), B. Sbarufatti (INAF-OAB/PSU), D.N. Burrows (PSU), S.L. Gibson (U. Leicester), J.P. Osborne (U. Leicester) and B. Mingo report on behalf of the Swift-XRT team: We have analysed 6.5 ks of XRT data for GRB 160826A (Mingo et al. GCN Circ. 19866), from 93 s to 22.1 ks after the BAT trigger. The data comprise 114 s in Windowed Timing (WT) mode (the first 5 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode. The refined XRT position is RA, Dec = 183.1127, -67.6639 which is equivalent to: RA (J2000): 12 12 27.05 Dec(J2000): -67 39 50.0 with an uncertainty of 3.5 arcsec (radius, 90% confidence). The light curve can be modelled with a power-law decay with a decay index of alpha=1.64 (+0.06, -0.05). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.68 (+0.31, -0.28). The best-fitting absorption column is 9.1 (+3.3, -2.7) x 10^21 cm^-2, in excess of the Galactic value of 4.6 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 5.7 x 10^-11 (8.5 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 9.1 (+3.3, -2.7) x 10^21 cm^-2 Galactic foreground: 4.6 x 10^21 cm^-2 Excess significance: 2.7 sigma Photon index: 1.68 (+0.31, -0.28) If the light curve continues to decay with a power-law decay index of 1.64, the count rate at T+24 hours will be 2.1 x 10^-4 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.2 x 10^-14 (1.7 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/00709907. This circular is an official product of the Swift-XRT team.