TITLE: GCN CIRCULAR NUMBER: 38945 SUBJECT: GRB 250114A: Swift-XRT refined Analysis DATE: 25/01/14 19:41:44 GMT FROM: Phil Evans at U of Leicester pae9@star.le.ac.uk

S. Dichiara (PSU), J.A. Kennea (PSU), K.L. Page (U. Leicester), A.P. Beardmore (U. Leicester), V. D'Elia (SSDC & INAF-OAR), B. Sbarufatti (INAF-OAB), C. Salvaggio (INAF-OAB), D.N. Burrows (PSU) and P.A. Evans report on behalf of the Swift-XRT team:

We have analysed 8.6 ks of XRT data for GRB 250114A, from 117 s to 28.1 ks after the BAT trigger. The data comprise 317 s in Windowed Timing (WT) mode (the first 9 s were taken while Swift was slewing) with the remainder in Photon Counting (PC) mode.

The late-time light curve (from T0+4.6 ks) can be modelled with an initial rise, with a power-law index of alpha=-0.94 (+1.18, -0.25), followed by a break at T+8035 s to an alpha of 1.32 (+0.31, -0.29).

A spectrum formed from the WT mode data can be fitted with an absorbed power-law with a photon spectral index of 1.09 (+/-0.03). The best-fitting absorption column is 1.8 (+/-0.9) x 10^22 cm^-2, at a redshift of 4.732, in addition to the Galactic value of 5.1 x 10^20 cm^-2 (Willingale et al. 2013). The PC mode spectrum has a photon index of 1.87 (+0.14, -0.13) and a best-fitting absorption column of 1.0 (+2.2, -1.0) x 10^22 cm^-2. The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 3.6 x 10^-11 (4.1 x 10^-11) erg cm^-2 count^-1.

A summary of the PC-mode spectrum is thus: Galactic foreground: 5.1 x 10^20 cm^-2 Intrinsic column: 1.0 (+2.2, -1.0) x 10^22 cm^-2 at z=4.732 Photon index: 1.87 (+0.14, -0.13)

If the light curve continues to decay with a power-law decay index of 1.32, the count rate at T+24 hours will be 6.8 x 10^-3 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 2.4 x 10^-13 (2.8 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/01281241.

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

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