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GCN Circular 23813

GRB 190129B: Swift-XRT candidate afterglow detection
2019-01-30T09:11:11Z (5 years ago)
Andrea Melandri at INAF-OAB <>
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
The results of the full analysis of the tiled XRT observations are
available at

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