GCN Circular 19036
J. R. Cummings (NASA/UMBC) reports on behalf of the Swift-XRT team: We have analysed 6.0 ks of XRT data for GRB 160220B (Cummings et al. GCN Circ. 19029), from 3.3 ks to 16.9 ks after the BAT trigger. The data are entirely in Photon Counting (PC) mode. Using 4686 s of PC mode data and 8 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 = 259.86518, -18.12401 which is equivalent to: RA (J2000): 17h 19m 27.64s Dec(J2000): -18d 07' 26.5" with an uncertainty of 1.5 arcsec (radius, 90% confidence). The light curve can be modelled with a power-law decay with a decay index of alpha=1.37 (+0.18, -0.17). A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.17 (+0.25, -0.23). The best-fitting absorption column is 4.3 (+1.2, -1.1) x 10^21 cm^-2, in excess of the Galactic value of 2.6 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 3.6 x 10^-11 (6.3 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 4.3 (+1.2, -1.1) x 10^21 cm^-2 Galactic foreground: 2.6 x 10^21 cm^-2 Excess significance: 2.5 sigma Photon index: 2.17 (+0.25, -0.23) If the light curve continues to decay with a power-law decay index of 1.37, the count rate at T+24 hours will be 2.7 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 9.7 x 10^-14 (1.7 x 10^-13) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00674734. This circular is an official product of the Swift-XRT team.