TITLE: GCN CIRCULAR NUMBER: 9155 SUBJECT: GRB 090417B: Swift-XRT refined analysis DATE: 09/04/18 16:55:25 GMT FROM: Boris Sbarufatti at INAF-IASF-Pa Sbarufatti B., Mangano V. (INAF-IASFPA) report on behalf of the Swift Team: We have analysed the first six orbits of Swift-XRT data obtained from GRB 090417B (trigger 349450; Sbarufatti, et al., GCN Circ. 9135), comprising 1456 s taken in Windowed Timing (WT) mode, from T+393 s to T+2.0 ks, and a total exposure of 9.2 ks in Photon Counting (PC) mode divided in 192 s from T+1.1 ks to T+1.3 ks and 9.0 ks from T+5.4 ks to the end of the observation at T+30 ks. Using 6972 s of XRT Photon Counting mode data and 9 UVOT images, we find an astrometrically corrected X-ray position (using the XRT-UVOT alignment and matching to the USNO-B1 catalogue): RA, Dec = 209.6942, 47.0182 which is equivalent to: RA (J2000): 13 58 46.62 Dec (J2000): +47 01 05.4 with an uncertainty of 1.4 arcsec (90% confidence). This position lies 4.8 arcmin from the BAT refined position, outside the quoted error circle (Cummings, et al., GCN circ. 9139). The 0.3-10 keV X-ray light curve of the first orbit is dominated by flaring activity, with 3 major peaks at ~T+530, ~T+1410 s and ~T+1560 s respectively. From the second orbit on the light-curve is decaying according to a power-law with slope -1.21+/-0.05. If decaying at this rate, the afterglow will reach a count-rate of 1.98E-2 counts/s at T+48h. The average WT spectrum of the first orbit is best fitted by an absorbed power-law model with a high energy cutoff. The best fit parameters are photon index 0.40+/-0.17, cutoff energy 3.1+/-0.4 keV and NH (9.2+/-0.6)E21 cm^-2, in large excess with respect to the galactic value 1.6E20 cm^-2 (Kalberla et al. 2005). The average observed(unabsorbed) flux in the 0.3-10 keV band is 1.6(2.1)E-9 ergs cm^-2 s^-1. The average spectrum of the large double peaked flare between T+1.3 ks and T+2.0 ks is also fitted by an absorbed power-law model with a high energy cutoff with best fit parameters photon index 0.46+/-0.2, cutoff energy 3.2+/-0.5 and NH (9.5+/-0.7)E21 cm^-2. The average PC spectrum in the T+5.4 ks - T+30 ks interval is well fitted by an absorbed power-law with photon index 2.0+/-0.1 and NH (9.6+/-0.10E21 cm^-2. The average observed(unabsorbed) flux in the 0.3-10 keV band is 2.8(5.6)E-11 ergs cm^-2 s^-1. The count-rate to flux conversion factor is 1.0E-10. All quoted errors are at 90% confidence level. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00349450. This circular is an official product of the Swift-XRT team.