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Time-Variable Emission from Transiently Accreting Neutron Stars in Quiescence due to Deep Crustal Heating

Ushomirsky, Greg and Rutledge, R. E. (2001) Time-Variable Emission from Transiently Accreting Neutron Stars in Quiescence due to Deep Crustal Heating. Monthly Notices of the Royal Astronomical Society, 325 (3). pp. 1157-1166. ISSN 0035-8711.

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Transiently accreting neutron stars in quiescence ðLX & 1034 erg s21Þ have been observed to vary in intensity by factors of few, over time-scales of days to years. If the quiescent luminosity is powered by a hot neutron star core, the core cooling time-scale is much longer than the recurrence time, and cannot explain the observed, more rapid variability. However, the non-equilibrium reactions which occur in the crust during outbursts deposit energy in isodensity shells, from which the thermal diffusion time-scale to the photosphere is days to years. The predicted magnitude of variability is too low to explain the observed variability unless – as is widely believed – the neutrons beyond the neutron-drip density are superfluid. Even then, the variability due to this mechanism in models with standard core neutrino cooling processes is less than 50 per cent – still too low to explain the reported variability. However, models with rapid core neutrino cooling can produce a variability by a factor as great as 20, on time-scales of days to years following an outburst. Thus, the factors of ,few intensity variability observed from transiently accreting neutron stars can be accounted for by this mechanism only if rapid core cooling processes are active.

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Additional Information:Copyright 2001 Royal Astronomical Society. Accepted 2001 March 20. Recieved 2001 March 15. In original form 2001 January 17. The authors gratefully acknowledge useful conversations with Ed Brown and Lars Bildsten, with whom this idea was initially discussed, and whose comments improved this paper. The authors also thank Dimitri Yakovlev for his extensive comments on this paper. This work was supported in part by NASA Grants NAG5-3239 and NGC5-7034, and NSF Grant AST-9618537. GU acknowledges the support of Lee A. DuBridge as a postdoctoral scholar
Group:Space Radiation Laboratory
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Space Radiation Laboratory2001-03
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ID Code:55230
Deposited By: Deborah Miles
Deposited On:27 Feb 2015 02:49
Last Modified:03 Oct 2019 08:04

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