Thermal Emission in the Quiescent Neutron Star SAX J1810.8-2609

Jessamyn L. Allen, Jeroen Homan, Deepto Chakrabarty, Michael Nowak
2018 Astrophysical Journal  
We have observed the neutron star low-mass X-ray binary SAX J1810.8−2609 in quiescence with XMM-Newton. SAX J1810.8−2609 is one of the faintest non-pulsing neutron star low-mass X-ray binaries in quiescence and previously only had upper limits on its quiescent thermal emission. We found SAX J1810.8−2609 at the same 0.5-10 keV, unabsorbed luminosity as the previous quiescent observation in 2003, = Ĺ 1.5 10 X 32 erg s −1 . We show that the spectrum requires both thermal and nonthermal components,
more » ... each contributing approximately half the total emission. The low neutron star luminosity suggests a time-averaged outburst accretion rate of » -Ṁ 10 12 M e yr −1 , in conflict with its observed outburst activity corresponding to a mass accretion rate that is an order of magnitude larger ( » -Ṁ 10 11 M e yr −1 ). Our observation designates SAX J1810.8−2609 more firmly as a member of a population of faint quiescent neutron star LMXBs whose quiescent thermal luminosity is not aligned with standard cooling models.
doi:10.3847/1538-4357/aaa6d3 fatcat:ikctav7wdbavpkl55slpwdatxy