Crucial role of neutron diffusion in the crust of accreting neutron stars

Chugunov, A. I.; Shchechilin, N N

doi:10.1093/mnrasl/slaa055

Cited by 11 publications

(10 citation statements)

References 33 publications

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“…In this work we have used the models by Haensel & Zdunik (2008) and Fantina et al (2018) for the deep crustal heating. Recently, Chugunov & Shchechilin (2020) and Gusakov & Chugunov (2020) have shown that diffusion of neutrons in the inner crust, neglected in the previous studies, can be essential for composition, equation of state, and heating of the accreted inner crust. An impact of these effects on thermal evolution of transiently accreting neutron stars remains to be studied in a future work.…”

Section: Discussionmentioning

confidence: 99%

Crust structure and thermal evolution of neutron stars in soft X-ray transients

Potekhin

Chabrier

2021

A&A

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Context. Thermal evolution of neutron stars in soft X-ray transients (SXTs) is sensitive to the equation of state, nucleon superfluidity, composition and structure of the crust. Comparison of observations of their crust cooling with simulations is a powerful tool of verification of theoretical models of the dense matter. Aims. We study the effect of physics input on thermal evolution of neutron stars in SXTs. In particular, we consider different modern models of the sources of deep crustal heating during accretion episodes and the effects brought about by impurities embedded in the crust during its formation. Methods. We simulate thermal structure and evolution of episodically accreting neutron stars under different assumptions on the crust composition and on the distribution of heat sources and impurities. For the nonaccreted crust, we consider the nuclear charge fluctuations that arise at crust formation. For the accreted crust, we compare different theoretical models of composition and internal heating. We also compare results of numerical simulations with observations of the crust cooling in SXT MXB 1659−29. Results. The nonaccreted part of the inner crust of a neutron star can have a layered structure, with almost pure crystalline layers interchanging with layers composed of mixtures of different nuclei. The latter layers have relatively low thermal conductivities, which affects thermal evolution of the transients. The impurity distribution in the crust strongly depends on the models of the dense matter and the crust formation scenario. The shallow heating that is needed to reach agreement between the theory and observations depends on characteristics of the crust and envelope.

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Section: Discussionmentioning

confidence: 99%

Crust structure and thermal evolution of neutron stars in soft X-ray transients

Potekhin

Chabrier

2021

A&A

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“…Besides, we adopt Ref. [11] as the traditional deep crustal heating input, an improved deep crustal heating model by considering the diffusion of neutrons in the inner crust is proposed [13][14][15]. It's also interesting to investigate the quiescent luminosity of SXTs with this modern deep crustal heating.…”

Section: Discussionmentioning

confidence: 99%

“…Observed quiescent luminosities of transiently accreting neutron stars are generally believed to be held by deep crustal heating with the release of ∼ 1 − 2 MeV per accreted nucleon [8][9][10][11][12], which is produced by the non-equilibrium nuclear reactions such as electron captures, neutron emission/absorption and pycnonuclear reaction due to the continuous compression during outburst phase. It's worth to mention that Chugunov and collaborators have pointed out that the mobility of neutrons in the inner crust could strongly suppress the heat release and drastically change its distribution over density [13][14][15], compared with the conventional deep crustal heating models (Hasensel et al Refs. [8][9][10][11][12]).…”

Section: Introductionmentioning

confidence: 99%

Quiescent luminosities of transiently accreting neutron stars with neutrino heating due to charged pion decay

Liu,

Dai,

et al. 2021

Preprint

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We study the quiescent luminosities of accreting neutron stars by a new mechanism as neutrino heating for additional deep crustal heating, where the neutrino heating is produced by charged pions decay from the nuclear collisions on the surface of neutron star during its active accretion. For low mass neutron star( 1.4 M⊙), as the neutrino heating is little( 1 MeV per accreted nucleon) or there would be no neutrino heating, the quiescent luminsoity will be not affected or slightly affected. While for massive neutron star ( 2 M⊙), the quiescent luminosity will be enhanced more obviously with neutrino heating in the range 2-6 MeV per accreted nucleon. The observations on cold neutron stars such as 1H 19605+00, SAX J1808.4-3658 can be explained with neutrino heating if a fast cooling and heavy elements surface are considered. The observations on a hot neutron star such as RX J0812.4-3114 can be explained with neutrino heating if the direct Urca process is forbidden for a massive star with light elements surface, which is different from the previous work that the hot observations should be explained with small mass neutron star and the effect of superfluidity.

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“…Namely, all of them implicitly neglect the redistribution of unbound neutrons in the inner crust. It has recently been shown that this approximation is incorrect (Chugunov & Shchechilin 2020) and leads to violation of the neutron hydrostatic/diffusion (nHD) equilibrium in the inner crust (Gusakov & Chugunov 2020, hereafter GC20). In fact, the nHD equilibrium condition, given by µ ∞ n ≡ µne ν/2 = const (here µn is the local neutron chemical potential, including the rest mass and e ν/2 is the redshift factor), should be considered simultaneously with the hydrostatic TOV equations.…”

Section: Introductionmentioning

confidence: 99%

Accreting neutron stars: heating of the upper layers of the inner crust

Shchechilin,

Gusakov,

Chugunov

2022

Preprint

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Neutron stars in low-mass X-ray binaries are thought to be heated up by accretion-induced exothermic nuclear reactions in the crust. The energy release and the location of the heating sources are important ingredients of the thermal evolution models. Here we present thermodynamically consistent calculations of the energy release in three zones of the stellar crust: at the outer-inner crust interface, in the upper layers of the inner crust (up to the density ρ 2 × 10 12 g cm −3 ), and in the underlying crustal layers. We consider three representative models of thermonuclear ashes (Superburst, Extreme rp, and Kepler ashes). The energy release in each zone is parametrized by the pressure at the outer-inner crust interface, which encodes all uncertainties related to the physics of the deepest inner-crust layers. Our calculations allow us, in particular, to set new lower limits on the net energy release (per accreted baryon): Q 0.28 MeV for Extreme rp ashes and Q 0.43 − 0.51 MeV for Superburst and Kepler ashes.

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Crucial role of neutron diffusion in the crust of accreting neutron stars

Cited by 11 publications

References 33 publications

Crust structure and thermal evolution of neutron stars in soft X-ray transients

Crust structure and thermal evolution of neutron stars in soft X-ray transients

Quiescent luminosities of transiently accreting neutron stars with neutrino heating due to charged pion decay

Accreting neutron stars: heating of the upper layers of the inner crust

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