TITLE: GCN CIRCULAR NUMBER: 28808 SUBJECT: GRB 201029A: Swift-XRT refined Analysis DATE: 20/10/30 10:11:05 GMT FROM: Phil Evans at U of Leicester M. Perri (ASDC), V. D'Elia (ASDC), A. D'Ai (INAF-IASFPA), B. Sbarufatti (PSU), D.N. Burrows (PSU), J. D. Gropp (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester) and S. Dichiara (NASA/GSFC/UMCP) reporton behalf of the Swift-XRT team: We have analysed 6.2 ks of XRT data for GRB 201029A (Dichiara et al. GCN Circ. 28803), from 128 s to 34.7 ks after the BAT trigger. The data comprise 764 s in Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode. The enhanced XRT position for this burst was given by Beardmore et al. (GCN Circ. 28806). The light curve is dominated by flares. The first flare covers ~T0+200-650 s. The second flare started at T0+1100s and was still ongoing when the GRB entered Earth eclipse at T0+1850 s. The third flare began at T0+11.5 ks, was still ongoing at T0+23 ks and finished at some point before T0+30.5 ks, although large observing gaps in this window prevent acccurate measurements of the flare and it is possible that there are multiple flares at this time rather than a single long-lived flare. This behaviour, of multiple flares dominating the XRT light curve for tens of kiloseconds, is reminiscent of GRBs 050904, 121027A and 130925A (see https://www.swift.ac.uk/xrt_curves/allcurves.php for a mugshot gallery of all XRT GRB afterglows). This flaring activity makes it difficult to model the underlying behaviour. Excluding all of the above times, the light curve can be modelled with a power-law decay with a decay index of alpha=0.79 (+0.05, -0.06). These formal errors are likely underestimates, since they depend on how accurate the estimates of flare times are, which are themselves subject to proper modelling of the underlying emission. A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.65 (+/-0.05). The best-fitting absorption column is 4.9 (+/-0.3) x 10^21 cm^-2, in excess of the Galactic value of 2.1 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 1.97 (+/-0.12) and a best-fitting absorption column of 2.9 (+/-0.5) x 10^21 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.7 x 10^-11 (5.4 x 10^-11) erg cm^-2 count^-1. A summary of the PC-mode spectrum is thus: Total column: 2.9 (+/-0.5) x 10^21 cm^-2 Galactic foreground: 2.1 x 10^20 cm^-2 Excess significance: 9.6 sigma Photon index: 1.97 (+/-0.12) If the light curve continues to decay with a power-law decay index of 0.79, the count rate at T+24 hours will be 0.024 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 9.2 x 10^-13 (1.3 x 10^-12) erg cm^-2 s^-1. The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01003002. This circular is an official product of the Swift-XRT team.