GCN Circular 28341

J.A. Kennea (PSU), J.P. Osborne (U. Leicester), K.L. Page (U.
Leicester), P. D'Avanzo (INAF-OAB), M.G. Bernardini (INAF-OAB), E.
Ambrosi  (INAF-IASFPA) , A. Tohuvavohu (U. Toronto), B. Sbarufatti
(PSU) and K. K. Simpson (PSU) report on behalf of the Swift-XRT team:

We have analysed 2.5 ks of XRT data for GRB 200901A (Simpson et al. GCN
Circ. 28335
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 ), from 3.1 ks to 11.1 ks after the	BAT trigger. The data
are entirely in Photon Counting (PC) mode. Using 1707 s of PC mode data
and 4 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 = 61.78319, -59.89084 which is equivalent to:

RA (J2000): 04h 07m 07.97s
Dec(J2000): -59d 53' 27.0"

with an uncertainty of 1.8 arcsec (radius, 90% confidence).

The light curve can be modelled with a power-law decay with a decay
index of alpha=0.95 (+0.28, -0.24).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 2.31 (+0.30, -0.28). The
best-fitting absorption column is  2.2 (+0.9, -0.8) x 10^21 cm^-2, in
excess of the Galactic value of 1.5 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 3.0 x 10^-11 (4.8 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     2.2 (+0.9, -0.8) x 10^21 cm^-2
Galactic foreground: 1.5 x 10^20 cm^-2
Excess significance: 4.2 sigma
Photon index:	     2.31 (+0.30, -0.28)

If the light curve continues to decay with a power-law decay index of
0.95, the count rate at T+24 hours will be 7.9 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.3 x
10^-13 (3.8 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/00994143.

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