XMM-Newton observations of the neutron star X-ray transient KS 1731-260 in quiescence
Abstract
We report on XMM-Newton observations performed on 2001 September 13-14 of the neutron star X-ray transient KS 1731-260 in quiescence. The source was detected at an unabsorbed 0.5-10 keV flux of only 4 - 8 x 10-14 erg/s, depending on the model used to fit the data, which for a distance of 7 kpc implies a 0.5-10 keV X-ray luminosity of approximately 2 - 5 x 1032 erg/s. The September 2001 quiescent flux of KS 1731-260 is lower than that observed during the Chandra observation in March 2001. In the cooling neutron star model for the quiescent X-ray emission of neutron star X-ray transients, this decrease in the quiescent flux implies that the crust of the neutron star in KS 1731-260 cooled down rapidly between the two epochs, indicating that the crust has a high conductivity. Furthermore, enhanced cooling in the neutron star core is also favored by our results.
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