GCN Circular 23813

S. J. LaPorte (PSU), J.A. Kennea (PSU), J.P. Osborne (U. Leicester),
K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), P. D'Avanzo
(INAF-OAB), V. D'Elia (ASDC), A. D'Ai (INAF-IASFPA), B. Sbarufatti
(INAF-OAB/PSU) and P.A. Evans (U. Leicester) report on behalf of the
Swift-XRT team:

Swift-XRT has performed follow-up observations of the IPN-detected
burst GRB 190129B in a series of observations tiled on the sky. The
total exposure time is 6.3 ks, distributed over 14 tiles; the maximum
exposure at a single sky location was 1.1 ks. The data were collected
between T0+45.0 ks and T0+60.4 ks, and are entirely in Photon Counting
(PC) mode. 

An uncatalogued X-ray source is detected and is above the RASS limit,
and is therefore likely the GRB afterglow. Using 42 s of PC mode data
and 1 UVOT image, we find an enhanced XRT position (using the XRT-UVOT
alignment and matching UVOT field sources to the USNO-B1 catalogue):
RA, Dec = 117.46104, +0.93484 which is equivalent to:

RA (J2000): 07h 49m 50.65s
Dec(J2000): +00d 56' 05.4"

with an uncertainty of 3.0 arcsec (radius, 90% confidence). This
position is about 7 arcmin from the edge of the IPN 3 sigma error box
(Hurley et al., GCN Circ 23808).  The light curve is consistent with a
constant source of mean count rate 4.4e-01 ct/sec. A power-law fit
gives an index of 1.2 (+1.6, -2.1).

A spectrum formed from the PC mode data can be fitted with an absorbed
power-law with a photon spectral index of 1.8 (+/-0.4). The
best-fitting absorption column is  4.7 (+2.8, -2.1) x 10^21 cm^-2, in
excess of the Galactic value of 7.3 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 4.4 x 10^-11 (6.3 x 10^-11) erg
cm^-2 count^-1. 

A summary of the PC-mode spectrum is thus:
Total column:	     4.7 (+2.8, -2.1) x 10^21 cm^-2
Galactic foreground: 7.3 x 10^20 cm^-2
Excess significance: 3.1 sigma
Photon index:	     1.8 (+/-0.4)

The results of the XRT-team automatic analysis of the likely afterglow
are at http://www.swift.ac.uk/xrt_products/TILED_GRB00076/Source1.php.
The results of the full analysis of the tiled XRT observations are
available at http://www.swift.ac.uk/xrt_products/TILED_GRB00076.

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