TITLE: GCN CIRCULAR NUMBER: 36982 SUBJECT: GRB 240730A: Swift-XRT refined Analysis DATE: 24/07/30 16:44:42 GMT FROM: Phil Evans at U of Leicester pae9@star.le.ac.uk
S. Dichiara (PSU), J.P. Osborne (U. Leicester), K.L. Page (U. Leicester), M. Ferro (INAF-OAB), R. Brivio (INAF-OAB), A. D'Ai (INAF-IASFPA), J.A. Kennea (PSU), A. Tohuvavohu (U. Toronto) and P.A. Evans report on behalf of the Swift-XRT team:
We have analysed 7.2 ks of XRT data for GRB 240730A, from 113 s to 23.5 ks after the BAT trigger. The data comprise 14 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 light curve can be modelled with a power-law decay with a decay index of alpha=2.04 (+/-0.24).
A spectrum formed from the PC mode data can be fitted with an absorbed power-law with a photon spectral index of 1.6 (+/-0.4). The best-fitting absorption column is 1.4 (+0.6, -0.5) x 10^22 cm^-2, in excess of the Galactic value of 7.8 x 10^21 cm^-2 (Willingale et al. 2013). The counts to observed (unabsorbed) 0.3-10 keV flux conversion factor deduced from this spectrum is 6.8 x 10^-11 (1.0 x 10^-10) erg cm^-2 count^-1.
A summary of the PC-mode spectrum is thus: Total column: 1.4 (+0.6, -0.5) x 10^22 cm^-2 Galactic foreground: 7.8 x 10^21 cm^-2 Excess significance: 2.1 sigma Photon index: 1.6 (+/-0.4)
If the light curve continues to decay with a power-law decay index of 2.04, the count rate at T+24 hours will be 5.4 x 10^-6 count s^-1, corresponding to an observed (unabsorbed) 0.3-10 keV flux of 3.6 x 10^-16 (5.7 x 10^-16) erg cm^-2 s^-1.
The results of the XRT-team automatic analysis are available at http://www.swift.ac.uk/xrt_products/01245636.
This circular is an official product of the Swift-XRT team.
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