TITLE:   GCN CIRCULAR
NUMBER:  36182
SUBJECT: GRB 240419A: Swift-XRT refined Analysis
DATE:    24/04/19 15:20:33 GMT
FROM:    Phil Evans at U of Leicester <pae9@star.le.ac.uk>

A.P. Beardmore (U. Leicester), J.P. Osborne (U. Leicester), M. Perri
(SSDC & INAF-OAR), V. D'Elia (SSDC & INAF-OAR), B. Sbarufatti
(INAF-OAB), D.N. Burrows (PSU), J. D. Gropp (PSU), S. Dichiara (PSU)
and P.A. Evans report on behalf of the Swift-XRT team:

We have analysed 7.8 ks of XRT data for GRB 240419A, from 117 s to 33.6
ks after the  BAT trigger. The data are entirely in Photon Counting
(PC) mode. 

The light curve can be modelled with a series of power-law decays. The
initial decay index is alpha=5.3 (+2.7, -0.8). At T+249 s  the decay
flattens to an alpha of -0.2 (+0.7, -0.6) before breaking again at
T+1406 s to a final decay with index alpha=1.20 (+0.32, -0.25).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.30 (+0.30, -0.27). The
best-fitting absorption column is  2.4 (+1.1, -0.9) x 10^21 cm^-2, in
excess of the Galactic value of 6.6 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 3.1 x 10^-11 (5.1 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     2.4 (+1.1, -0.9) x 10^21 cm^-2
Galactic foreground: 6.6 x 10^20 cm^-2
Excess significance: 3.1 sigma
Photon index:	     2.30 (+0.30, -0.27)

If the light curve continues to decay with a power-law decay index of
1.20, the count rate at T+24 hours will be 2.8 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 8.7 x
10^-14 (1.4 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/01222955.

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