TITLE: GCN CIRCULAR NUMBER: 35443 SUBJECT: GRB 231230A: Swift-XRT refined Analysis DATE: 23/12/30 16:44:29 GMT FROM: Phil Evans at U of Leicester pae9@star.le.ac.uk
A. Tohuvavohu (U. Toronto), D.N. Burrows (PSU), J. D. Gropp (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), R. Brivio (INAF-OAB), A. D'Ai (INAF-IASFPA), A. Melandri (INAF-OAR) and P.A. Evans report on behalf of the Swift-XRT team:
We have analysed 9.1 ks of XRT data for GRB 231230A, from 127 s to 41.2 ks after the BAT trigger. The data comprise 68 s in Windowed Timing (WT) mode (the first 8 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode.
The light curve can be modelled with an initial power-law decay with an index of alpha=0.835 (+0.027, -0.028), followed by a break at T+17.4 ks to an alpha of 2.0 (+/-0.4).
A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.93 (+/-0.13). The best-fitting absorption column is 4.0 (+0.7, -0.6) x 10^21 cm^-2, in excess of the Galactic value of 1.3 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 4.1 x 10^-11 (6.1 x 10^-11) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus: Total column: 4.0 (+0.7, -0.6) x 10^21 cm^-2 Galactic foreground: 1.3 x 10^20 cm^-2 Excess significance: 9.9 sigma Photon index: 1.93 (+/-0.13)
If the light curve continues to decay with a power-law decay index of 2.0, the count rate at T+24 hours will be 5.1 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.1 x 10^-13 (3.1 x 10^-13) erg cm^-2 s^-1.
The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01205319.
This circular is an official product of the Swift-XRT team.
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