[vsnet-grb-info 25043] GRB 200219A: Swift-XRT refined Analysis correction

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  27142
SUBJECT: GRB 200219A: Swift-XRT refined Analysis correction
DATE:    20/02/19 19:03:51 GMT
FROM:    Elena Ambrosi at INAF-IASF  <elena.ambrosi at inaf.it>

A. D'Ai (INAF-IASFPA), B. Sbarufatti (PSU), D.N. Burrows (PSU), J. D.
Gropp (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), A.
Melandri (INAF-OAB), T. Sbarrato (INAF-OAB) and A. Y. Lien (GSFC/UMBC)
report on behalf of the Swift-XRT team:

We have analysed 9.8 ks of XRT data for GRB 200219A (Lien et al. GCN
Circ. 27125), from 57 s to 24.9 ks after the  BAT trigger. The data
comprise 165 s in Windowed Timing (WT) mode (the first 8 s were taken
while Swift was slewing) with the remainder in Photon Counting (PC)
mode. The enhanced XRT position for this burst was given by Osborne et
al. (GCN Circ. 27138).

The light curve can be modelled with a series of power-law decays. The
initial decay index is alpha=1.10 (+/-0.16). At T+136 s  the decay
steepens to an alpha of 4.7 (+3.3, -0.4) before breaking again at T+444
s to a final decay with index alpha=1.2 (+0.4, -0.6).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.36 (+/-0.06). The
best-fitting absorption column is  1.26 (+0.26, -0.24) x 10^21 cm^-2,
in excess of the Galactic value of 1.9 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 4.9 x 10^-11 (5.4 x 10^-11) erg
cm^-2 count^-1. 

A summary of the WT-mode spectrum is thus:
Total column:	     1.26 (+0.26, -0.24) x 10^21 cm^-2
Galactic foreground: 1.9 x 10^20 cm^-2
Excess significance: 7.2 sigma
Photon index:	     1.36 (+/-0.06)

If the light curve continues to decay with a power-law decay index of
1.2, the count rate at T+24 hours will be 2.1 x 10^-4 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.0 x
10^-14 (1.1 x 10^-14) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00957271.

Due to data delivery problems, the GCN Circ. 27139 (D'Elia et al.) was
sent while the analysis was still running, which is why it was
incomplete.

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