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Swift XRT observation of an X-ray burst of 1A 1246-588

ATel #875; A. K.H. Kong (MIT)
on 12 Aug 2006; 22:29 UT
Credential Certification: Albert Kong (akong@cfa.harvard.edu)

Subjects: X-ray, Binary, Neutron Star

Referred to by ATel #: 3482

We further analyzed the outburst of the X-ray burster 1A 1246-588 recently detected with Swift on 2006 August 11 (GCN #5436, Romano et al. 2006). Swift XRT began observation 193s after the BAT trigger; the X-ray light curve was clearly fading during the first ~500s and after that, the source count rate remained constant. We extracted time-resolved energy spectra for the first 400s. The spectra can be fitted with an absorbed blackbody model with temperature decreasing from 0.82 keV for the first 50s to 0.65 keV for the last 100s. The typical 90% error is about 0.03 keV. This suggests that the object is cooling during the decay. Excluding the first 2000s, we also fitted the spectrum of the persistent emission. The X-ray spectrum is consistent with an absorbed power-law model with a column density of 4.3+/-0.1 E21 cm^-2 and a photon index of 2.02+/-0.03 plus a Gaussian line at 0.65+/-0.02 keV. The absorbed 0.1-2.4 keV and 0.5-10 keV fluxes are 2E-10 and 5.8E-10 erg s^-1 cm^-2, consistent with previous ROSAT observation (IAUC # 6546 , Boller et al. 1997). We therefore suggest that the "outburst" detected with Swift is in fact a long Type-I X-ray burst with duration of at least 10 minutes.