TITLE: GCN CIRCULAR NUMBER: 40745 SUBJECT: GRB 250615A: Swift-XRT refined Analysis DATE: 25/06/16 10:56:50 GMT FROM: Phil Evans at U of Leicester pae9@star.le.ac.uk
D.N. Burrows (PSU), M.A. Williams (PSU), S. Dichiara (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), M.G. Bernardini (INAF-OAB), E. Ambrosi (INAF-IASFPA) , M. Capalbi (INAF-OAR) and P.A. Evans report on behalf of the Swift-XRT team:
We have analysed 6.2 ks of XRT data for GRB 250615A, from 93 s to 40.3 ks after the trigger. The data comprise 106 s in Windowed Timing (WT) mode with the remainder in Photon Counting (PC) mode.
The light curve can be modelled with a power-law decay with a decay index of alpha=1.62 (+0.07, -0.06).
A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.62 (+0.27, -0.26). The best-fitting absorption column is 2.4 (+0.6, -0.5) x 10^22 cm^-2, in excess of the Galactic value of 5.5 x 10^21 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 2.0 (+0.4, -0.3) and a best-fitting absorption column of 2.4 (+0.7, -0.6) x 10^22 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 6.7 x 10^-11 (1.5 x 10^-10) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus: Total column: 2.4 (+0.7, -0.6) x 10^22 cm^-2 Galactic foreground: 5.5 x 10^21 cm^-2 Excess significance: 5.3 sigma Photon index: 2.0 (+0.4, -0.3)
If the light curve continues to decay with a power-law decay index of 1.62, the count rate at T+24 hours will be 2.2 x 10^-4 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 1.5 x 10^-14 (3.3 x 10^-14) erg cm^-2 s^-1.
The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01324646.
This circular is an official product of the Swift-XRT team.
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