GCN Circular 27120

P. D'Avanzo (INAF-OAB) and P.A. Evans (U. Leicester) report on behalf
of the Swift-XRT team:

We have analysed 1.6 ks of XRT data for GRB 200216B (D'Avanzo et al.
GCN Circ. 27102
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 ), from 105 s to 1.7 ks after the  BAT trigger. The data
comprise 90 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 Goad et al.
(GCN Circ. 27106
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 ).

The light curve can be modelled with a power-law decay with a decay
index of alpha=1.91 (+0.07, -0.06).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.18 (+0.20, -0.19). The
best-fitting absorption column is  7.3 (+2.3, -1.9) x 10^21 cm^-2, in
excess of the Galactic value of 2.0 x 10^20 cm^-2 (Willingale et al.
2013). The PC mode spectrum has a photon index of 1.63 (+0.27, -0.26)
and a best-fitting absorption column of 9.2 (+2.9, -2.5) x 10^21 cm^-2.
The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor
deduced from this spectrum  is 5.8 x 10^-11 (8.5 x 10^-11) erg cm^-2
count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     9.2 (+2.9, -2.5) x 10^21 cm^-2
Galactic foreground: 2.0 x 10^20 cm^-2
Excess significance: 6.0 sigma
Photon index:	     1.63 (+0.27, -0.26)

If the light curve continues to decay with a power-law decay index of
1.91, the count rate at T+24 hours will be 5.4 x 10^-5 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 3.1 x
10^-15 (4.6 x 10^-15) erg cm^-2 s^-1.

The results of the XRT-team automatic analysis are available at
http://www.swift.ac.uk/xrt_products/00956824.

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