GCN Circular 27852
Subject
GRB 200528A: Swift-XRT refined Analysis
Date
2020-05-29T10:39:04Z (4 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
M. Perri (ASDC), V. D'Elia (ASDC), A. D'Ai (INAF-IASFPA), B. Sbarufatti
(PSU), D.N. Burrows (PSU), J. D. Gropp (PSU), J.P. Osborne (U.
Leicester), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester) and
E. Ambrosi report on behalf of the Swift-XRT team:
We have analysed 5.7 ks of XRT data for GRB 200528A (Ambrosi et al. GCN
Circ. 27832), from 73 s to 50.9 ks after the BAT trigger. The data
comprise 226 s in Windowed Timing (WT) mode with the remainder in
Photon Counting (PC) mode. The enhanced XRT position for this burst was
given by Evans et al. (GCN Circ. 27836).
The late-time light curve (from T0+5.1 ks) can be modelled with a
power-law decay with a decay index of alpha=0.97 (+/-0.07).
A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.30 (+/-0.05). The
best-fitting absorption column is 3.63 (+0.19, -0.18) x 10^21 cm^-2,
in excess of the Galactic value of 1.2 x 10^20 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 2.24 (+0.16, -0.15)
and a best-fitting absorption column of 3.8 (+0.7, -0.6) x 10^21 cm^-2.
The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum is 3.4 x 10^-11 (6.1 x 10^-11) erg cm^-2
count^-1.
A summary of the PC-mode spectrum is thus:
Total column: 3.8 (+0.7, -0.6) x 10^21 cm^-2
Galactic foreground: 1.2 x 10^20 cm^-2
Excess significance: 9.8 sigma
Photon index: 2.24 (+0.16, -0.15)
If the light curve continues to decay with a power-law decay index of
0.97, the count rate at T+24 hours will be 0.041 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.4 x
10^-12 (2.5 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/00974827.
This circular is an official product of the Swift-XRT team.