[vsnet-grb-info 22509] GRB 190519A: Swift-XRT refined Analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  24608
SUBJECT: GRB 190519A: Swift-XRT refined Analysis
DATE:    19/05/20 02:18:41 GMT
FROM:    Phil Evans at U of Leicester  <pae9 at leicester.ac.uk>

A. D'Ai (INAF-IASFPA), A. Melandri (INAF-OAB), P. D'Avanzo (INAF-OAB),
D.N. Burrows (PSU), A. Tohuvavohu (PSU), S. J. LaPorte (PSU), P.A.
Evans (U. Leicester), J.P. Osborne (U. Leicester), K.L. Page (U.
Leicester) and T.N. Ukwatta report on behalf of the Swift-XRT team:

We have analysed 7.0 ks of XRT data for GRB 190519A (Ukwatta et al. GCN
Circ. 24595), from 91 s to 46.8 ks after the  BAT trigger. The data
comprise 100 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. 24597).

The late-time light curve (from T0+13.7 ks) can be modelled with a
power-law decay with a decay index of alpha=1.33 (+/-0.28).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 2.34 (+0.20, -0.18). The
best-fitting absorption column is  6.5 (+1.2, -1.1) x 10^21 cm^-2, in
excess of the Galactic value of 4.3 x 10^21 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 1.79 (+0.13, -0.12)
and a best-fitting absorption column of 6.8 (+1.1, -1.0) x 10^21 cm^-2.
The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 4.9 x 10^-11 (7.5 x 10^-11) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     6.8 (+1.1, -1.0) x 10^21 cm^-2
Galactic foreground: 4.3 x 10^21 cm^-2
Excess significance: 4.3 sigma
Photon index:	     1.79 (+0.13, -0.12)

If the light curve continues to decay with a power-law decay index of
1.33, the count rate at T+24 hours will be 0.020 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.0 x
10^-12 (1.5 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/00904394.

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