GCN Circular 19036

J. R. Cummings (NASA/UMBC) reports on behalf of the Swift-XRT team:

We have analysed 6.0 ks of XRT data for GRB 160220B (Cummings et al.
GCN Circ. 19029
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 ), from 3.3 ks to 16.9 ks after the  BAT trigger. The
data are entirely in Photon Counting (PC) mode. Using 4686 s of PC mode
data and 8 UVOT images, we find an enhanced XRT position (using the
XRT-UVOT alignment and matching UVOT field sources to the USNO-B1
catalogue): RA, Dec = 259.86518, -18.12401 which is equivalent to:

RA (J2000): 17h 19m 27.64s
Dec(J2000): -18d 07' 26.5"

with an uncertainty of 1.5 arcsec (radius, 90% confidence).

The light curve can be modelled with a power-law decay with a decay
index of alpha=1.37 (+0.18, -0.17).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.17 (+0.25, -0.23). The
best-fitting absorption column is  4.3 (+1.2, -1.1) x 10^21 cm^-2, in
excess of the Galactic value of 2.6 x 10^21 cm^-2 (Willingale et al.
2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion
factor deduced from this spectrum  is 3.6 x 10^-11 (6.3 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     4.3 (+1.2, -1.1) x 10^21 cm^-2
Galactic foreground: 2.6 x 10^21 cm^-2
Excess significance: 2.5 sigma
Photon index:	     2.17 (+0.25, -0.23)

If the light curve continues to decay with a power-law decay index of
1.37, the count rate at T+24 hours will be 2.7 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 9.7 x
10^-14 (1.7 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/00674734.

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