TITLE:   GCN CIRCULAR
NUMBER:  36192
SUBJECT: GRB 240419B: Swift-XRT refined Analysis
DATE:    24/04/20 08:11:17 GMT
FROM:    Phil Evans at U of Leicester <pae9@star.le.ac.uk>

J.P. Osborne (U. Leicester), V. D'Elia (SSDC & INAF-OAR), B. Sbarufatti
(INAF-OAB), C. Salvaggio (INAF-OAB), J. D. Gropp (PSU), S. Dichiara
(PSU), J.A. Kennea (PSU), K.L. Page (U. Leicester) and P.A. Evans
report on behalf of the Swift-XRT team:

We have analysed 7.5 ks of XRT data for GRB 240419B, from 141 s to 52.1
ks after the  BAT trigger. The data comprise 282 s in Windowed Timing
(WT) mode (the first 6 s were taken while Swift was slewing) with the
remainder in Photon Counting (PC) mode. 

The late-time light curve (from T0+4.6 ks) can be modelled with a
power-law decay with a decay index of alpha=1.02 (+0.12, -0.11).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.95 (+/-0.05). The
best-fitting absorption column is  1.21 (+0.16, -0.15) x 10^21 cm^-2,
in excess of the Galactic value of 6.8 x 10^20 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 2.08 (+0.20, -0.19)
and a best-fitting absorption column of 1.2 (+/-0.5) x 10^21 cm^-2. The
counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 3.2 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: 6.8 x 10^20 cm^-2
Excess significance: 1.7 sigma
Photon index:	     2.08 (+0.20, -0.19)

If the light curve continues to decay with a power-law decay index of
1.02, the count rate at T+24 hours will be 10.0 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 3.2 x
10^-13 (4.2 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/01223072.

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