Skip to main content
New! October 18 GCN Classic Outage and Schema v4.2.0. See news and announcements

GCN Circular 23171

Subject
GRB 180823A: Swift-XRT refined Analysis
Date
2018-08-24T13:43:15Z (6 years ago)
From
Phil Evans at U of Leicester <pae9@leicester.ac.uk>
A. Tohuvavohu (PSU), S. J. LaPorte (PSU), S.L. Gibson (U. Leicester),
Z. Liu (NAOC / U. Leicester), J.P. Osborne (U. Leicester), P. D'Avanzo
(INAF-OAB), V. D'Elia (ASDC), A. D'Ai (INAF-IASFPA), J.A. Kennea (PSU)
and B. Sbarufatti report on behalf of the Swift-XRT team:

We have analysed 7.7 ks of XRT data for GRB 180823A (Sbarufatti et al.
GCN Circ. 23169), from 331 s to 39.4 ks after the  BAT trigger. The
data comprise 46 s 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. 23170).

The light curve can be modelled with a power-law decay with a decay
index of alpha=1.00 (+/-0.04).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.99 (+0.19, -0.18). The
best-fitting absorption column is  1.2 (+/-0.5) x 10^21 cm^-2, in
excess of the Galactic value of 1.2 x 10^20 cm^-2 (Willingale et al.
2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum  is 3.3 x 10^-11 (4.2 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     1.2 (+/-0.5) x 10^21 cm^-2
Galactic foreground: 1.2 x 10^20 cm^-2
Excess significance: 3.7 sigma
Photon index:	     1.99 (+0.19, -0.18)

If the light curve continues to decay with a power-law decay index of
1.00, the count rate at T+24 hours will be 0.013 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 4.3 x
10^-13 (5.3 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/00855434.

This circular is an official product of the Swift-XRT team.
Looking for U.S. government information and services? Visit USA.gov