[vsnet-grb-info 20732] GRB 180623A: Swift-XRT refined Analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  22830
SUBJECT: GRB 180623A: Swift-XRT refined Analysis
DATE:    18/06/23 23:56:06 GMT
FROM:    Phil Evans at U of Leicester  <pae9 at leicester.ac.uk>

J.A. Kennea (PSU), B. Sbarufatti (INAF-OAB/PSU), D.N. Burrows (PSU),
J.P. Osborne (U. Leicester), A.P. Beardmore (U. Leicester), P. D'Avanzo
(INAF-OAB), V. D'Elia (ASDC), A. D'Ai (INAF-IASFPA) and K.L. Page
report on behalf of the Swift-XRT team:

We have analysed 7.7 ks of XRT data for GRB 180623A (Page et al. GCN
Circ. 22828), from 83 s to 18.2 ks after the  BAT trigger. The data
comprise 90 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. 22829).

The late-time light curve (from T0+4.5 ks) can be modelled with a
power-law decay with a decay index of alpha=1.72 (+/-0.14).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.73 (+0.20, -0.19). The
best-fitting absorption column is  6.4 (+/-0.7) x 10^22 cm^-2, in
excess of the Galactic value of 1.5 x 10^22 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 2.04 (+0.27, -0.25)
and a best-fitting absorption column of 6.6 (+/-0.9) x 10^22 cm^-2. The
counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 9.0 x 10^-11 (2.9 x 10^-10) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     6.6 (+/-0.9) x 10^22 cm^-2
Galactic foreground: 1.5 x 10^22 cm^-2
Excess significance: 9.9 sigma
Photon index:	     2.04 (+0.27, -0.25)

If the light curve continues to decay with a power-law decay index of
1.72, the count rate at T+24 hours will be 2.3 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.0 x
10^-13 (6.5 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/00844015.

This circular is an official product of the Swift-XRT team.