GCN Circular 26130
Subject
GRB 191031C: Swift-XRT refined Analysis
Date
2019-11-01T18:56:03Z (5 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
D.N. Burrows (PSU), J. D. Gropp (PSU), P.A. Evans (U. Leicester), J.P.
Osborne (U. Leicester), K.L. Page (U. Leicester), M. Capalbi
(INAF-IASFPA), M. Perri (ASDC), A. Tohuvavohu (U. Toronto) and E.
Ambrosi report on behalf of the Swift-XRT team:
We have analysed 4.9 ks of XRT data for GRB 191031C (Ambrosi et al. GCN
Circ. 26108), from 87 s to 52.5 ks after the BAT trigger. The data
comprise 1.6 ks in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. The enhanced XRT position for this burst was
given by Goad et al. (GCN Circ. 26109).
The late-time light curve (from T0+6.6 ks) can be modelled with a
power-law decay with a decay index of alpha=1.06 (+0.17, -0.13).
A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.99 (+0.08, -0.06). The
best-fitting absorption column is 1.87 (+0.28, -0.08) x 10^21 cm^-2,
consistent with the Galactic value of 1.8 x 10^21 cm^-2 (Willingale et
al. 2013). The PC mode spectrum has a photon index of 1.79 (+0.12,
-0.05) and a best-fitting absorption column consistent with the
Galactic value. The counts to observed (unabsorbed) 0.3-10 keV flux
conversion factor deduced from this spectrum is 3.9 x 10^-11 (4.9 x
10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 1.8 (+0.4, -0.0) x 10^21 cm^-2
Galactic foreground: 1.8 x 10^21 cm^-2
Excess significance: <1.6 sigma
Photon index: 1.79 (+0.12, -0.05)
If the light curve continues to decay with a power-law decay index of
1.06, the count rate at T+24 hours will be 0.029 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.1 x
10^-12 (1.4 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/00932595.
This circular is an official product of the Swift-XRT team.