TITLE: GCN CIRCULAR NUMBER: 38823 SUBJECT: GRB 250103B: Swift-XRT refined Analysis DATE: 25/01/04 18:05:05 GMT FROM: Phil Evans at U of Leicester pae9@star.le.ac.uk
J.P. Osborne (U. Leicester), T. Sbarrato (INAF-OAB), P. D'Avanzo (INAF-OAB), M.G. Bernardini (INAF-OAB), D.N. Burrows (PSU), M. A. Williams (PSU), S. Dichiara (PSU), K.L. Page (U. Leicester) and P.A. Evans report on behalf of the Swift-XRT team:
We have analysed 3.5 ks of XRT data for GRB 250103B, from 144 s to 44.7 ks after the BAT trigger. The data comprise 31 s in Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode. The best available XRT position (using the promptly downlinked event data, the XRT-UVOT alignment and matching UVOT field sources to the USNO-B1 catalogue) is RA, Dec = 54.66413, -33.74945 which is equivalent to:
RA (J2000): 03 38 39.39 Dec(J2000): -33 44 58.0
with an uncertainty of 1.9 arcsec (radius, 90% confidence).
The light curve can be modelled with a power-law decay with a decay index of alpha=3.9 (+/-0.4).
A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 4.2 (+0.7, -0.5). The best-fitting absorption column is 6.3 (+6.6, -4.5) x 10^20 cm^-2, in excess of the Galactic value of 1.0 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 2.5 x 10^-11 (4.8 x 10^-11) erg cm^-2 count^-1.
A summary of the WT-mode spectrum is thus: Total column: 6.3 (+6.6, -4.5) x 10^20 cm^-2 Galactic foreground: 1.0 x 10^20 cm^-2 Excess significance: 2.0 sigma Photon index: 4.2 (+0.7, -0.5)
If the light curve continues to decay with a power-law decay index of 3.9, the count rate at T+24 hours will be 2.5 x 10^-10 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 6.3 x 10^-21 (1.2 x 10^-20) erg cm^-2 s^-1.
The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01278865.
This circular is an official product of the Swift-XRT team.
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