GCN Circular 36982

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.