An exceptionally cold neutron star in HETE J1900.1-2455
Abstract
The 1 km thick crust of neutron stars is strongly heated by nuclear reactions during accretion outbursts, but cools in quiescence. HETE J1900.1-2455 continously accreted since 2005, but in 2015 late Oct its intensity dropped below the detection limit of MAXI. Swift observations (Mar 7) fail to detect the source, implying Lx<e32 erg/s (0.5-10 keV) and a very cold neutron star crust of kT<65 eV. This is highly unexpected, as the crust should have been significantly heated during the 9 yr outburst: our studies of 5 other sources after >1 yr outbursts revealed hot neutron star crusts of >100 eV. This remarkable result suggests that nuclear heating may not always be efficient, a scenario that has never been considered to explain exceptionally cold neutron stars such as SAX J1808.4-3658 and 1H1905+000. With a 30 ks DDT, we can put firm constraints on the crust temperature in HETE J1900 (kT 33 eV; Lx 2e30 erg/s), with important implications for neutron star heating/cooling models.
- Publication:
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Chandra Proposal
- Pub Date:
- September 2015
- Bibcode:
- 2015cxo..prop.4818D