GCN Circular 35469

J. D. Gropp (PSU), J.P. Osborne (U. Leicester), K.L. Page (U.
Leicester), A. Melandri (INAF-OAR), T. Sbarrato (INAF-OAB), P. D'Avanzo
(INAF-OAB), S. Dichiara (PSU), J.A. Kennea (PSU) and P.A. Evans report
on behalf of the Swift-XRT team:

We have analysed 6.6 ks of XRT data for GRB 240102A, from 113 s to 28.3
ks after the  BAT trigger. The data comprise 91 s in Windowed Timing
(WT) mode (the first 10 s were taken while Swift was slewing) with the
remainder in Photon Counting (PC) mode. The best available XRT position
 (using the promptly downlinked event data, the XRT-UVOT alignment and
matching UVOT field sources to the USNO-B1 catalogue) is RA, Dec =
96.83800, -20.04076 which is equivalent to:

RA (J2000): 06 27 21.12
Dec(J2000): -20 02 26.7

with an uncertainty of 1.9 arcsec (radius, 90% confidence).

The late-time light curve (from T0+4.7 ks) can be modelled with a
power-law decay with a decay index of alpha=0.5 (+/-0.3).

A spectrum formed from the WT mode data can be fitted with an absorbed
power-law with a photon spectral index	of 1.74 (+0.11, -0.10). The
best-fitting absorption column is  3.3 (+0.6, -0.5) x 10^21 cm^-2, in
excess of the Galactic value of 2.3 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 4.3 x 10^-11 (5.7 x 10^-11) erg
cm^-2 count^-1. 

A summary of the WT-mode spectrum is thus:
Total column:	     3.3 (+0.6, -0.5) x 10^21 cm^-2
Galactic foreground: 2.3 x 10^21 cm^-2
Excess significance: 3.1 sigma
Photon index:	     1.74 (+0.11, -0.10)

If the light curve continues to decay with a power-law decay index of
0.5, the count rate at T+24 hours will be 9.8 x 10^-3 count s^-1,
corresponding to an observed (unabsorbed) 0.3-10 keV flux of 4.2 x
10^-13 (5.6 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/01205899.

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