2021MNRAS.508..882D -
Mon. Not. R. Astron. Soc., 508, 882-894 (2021/November-3)
Constraining the properties of dense neutron star cores: the case of the low-mass X-ray binary HETE J1900.1-2455.
DEGENAAR N., PAGE D., VAN DEN EIJNDEN J., BEZNOGOV M.V., WIJNANDS R. and REYNOLDS M.
Abstract (from CDS):
Measuring the time evolution of the effective surface temperature of neutron stars can provide invaluable information on the properties of their dense cores. Here, we report on a new Chandra observation of the transient neutron star low-mass X-ray binary HETE J1900.1-2455, which was obtained ≃2.5 yr after the end of its ≃10-yr long accretion outburst. The source is barely detected during the observation, collecting only six net photons, all below 2 keV. Assuming that the spectrum is shaped as a neutron star atmosphere model, we perform a statistical analysis to determine a 1σ confidence upper range for the neutron star temperature of ≃30-39 eV (for an observer at infinity), depending on its mass, radius, and distance. Given the heat injected into the neutron star during the accretion outburst, estimated from data provided by all-sky monitors, the inferred very low temperature suggests that the core either has a very high heat capacity or undergoes very rapid neutrino cooling. While the present data do not allow us to disentangle these two possibilities, both suggest that a significant fraction of the dense core is not superfluid/superconductor. Our modelling of the thermal evolution of the neutron star predicts that it may still cool further, down to a temperature of ≃15 eV. Measuring such a low temperature with a future observation may provide constraints on the fraction of baryons that is paired in the stellar core.
Abstract Copyright:
© 2021 The Author(s) Published by Oxford University Press on behalf of Royal Astronomical Society
Journal keyword(s):
accretion, accretion discs - dense matter - stars: neutron - X-rays: binaries - X-rays: individual: (HETE J1900.1-2455)
CDS comments:
MAXI J0556-532 is a misprint for MAXI J0556-332.
Simbad objects:
8
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