TITLE: GCN CIRCULAR NUMBER: 38918 SUBJECT: GRB 250106A: Swift-XRT afterglow detection DATE: 25/01/13 10:26:18 GMT FROM: Phil Evans at U of Leicester pae9@star.le.ac.uk
J.P. Osborne (U. Leicester), P. D'Avanzo (INAF-OAB), M.G. Bernardini (INAF-OAB), E. Ambrosi (INAF-IASFPA) , M. A. Williams (PSU), S. Dichiara (PSU), J.A. Kennea (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester) and P.A. Evans (U. Leicester) reports on behalf of the Swift-XRT team:
Swift-XRT has conducted further observations of the field of the SVOM/ECLAIRs-detected burst GRB 250106A. The observations now extend from T0+20.2 ks to T0+579.8 ks and have a total exposure time of 7.9 ks.
Of the sources previously reported, "Source 1" is fading with >3-sigma significance, and is therefore likely the GRB afterglow. Using 2981 s of PC mode data and 3 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 = 117.23873, +63.81242 which is equivalent to:
RA (J2000): 07h 48m 57.29s Dec(J2000): +63d 48' 44.7"
with an uncertainty of 3.0 arcsec (radius, 90% confidence). This position is 3.4 arcmin from the SVOM/ECLAIRs position. The source is fading with alpha >0.6.
A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 2.4 (+0.8, -0.7). The best-fitting absorption column is 3.7 (+3.4, -2.4) x 10^21 cm^-2, in excess of the Galactic value of 4.5 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 3.1 x 10^-11 (6.2 x 10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus: Total column: 3.7 (+3.4, -2.4) x 10^21 cm^-2 Galactic foreground: 4.5 x 10^20 cm^-2 Excess significance: 2.2 sigma Photon index: 2.4 (+0.8, -0.7)
The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/00021753. The results of the full analysis of the XRT observations are available at https://www.swift.ac.uk/ToO_GRBs/00021753.
This circular is an official product of the Swift-XRT team.
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