TITLE:   GCN CIRCULAR
NUMBER:  28990
SUBJECT: GRB 201203A: Swift-XRT afterglow detection
DATE:    20/12/03 15:11:51 GMT
FROM:    Kim Page at U.of Leicester  <klp5@leicester.ac.uk>

V. D'Elia (ASDC), 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.P. Beardmore (U. Leicester), A. Melandri
(INAF-OAB) and P.A. Evans (U. Leicester) report on behalf of the
Swift-XRT team:

Swift-XRT has observed GRB 201203A (Dichiara et al. GCN Circ. 28985),
collecting 2.8 ks of Photon Counting (PC) mode data between T0+4.7 ks
and T0+17.6 ks. 

One uncatalogued X-ray source is detected within the BAT error circle.
Using 857 s of PC mode data and 2 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 = 38.05521, -26.51820 which is
equivalent to:

RA (J2000): 02h 32m 13.25s
Dec(J2000): -26d 31' 05.5"

with an uncertainty of 3.3 arcsec (radius, 90% confidence). This
position is 107 arcsec from the BAT position. 

The light curve can be modelled with a power-law decay with a decay
index of alpha=1.4 (+1.3, -1.1).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.9 (+0.7, -0.4). The
best-fitting absorption column is  consistent with the Galactic value
of 1.8 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 3.3 x 10^-11 (1.6 x 10^-11) erg cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     1.8 (+/-7.3) x 10^20 cm^-2
Galactic foreground: 1.8 x 10^20 cm^-2
Excess significance: <1.6 sigma
Photon index:	     1.9 (+0.7, -0.4)

If the light curve continues to decay with a power-law decay index of
1.4, the count rate at T+24 hours will be 3.4 x 10^-4 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.1 x
10^-14 (5.5 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/01010946.
The results of the full analysis of the XRT observations are available
at https://www.swift.ac.uk/ToO_GRBs/01010946.

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