The radiative efficiency of neutron stars at low-level accretion

Abstract

When neutrons star low-mass X-ray binaries (NS-LMXBs) are in the low-level accretion regime (i.e., $L_{\mathrm{X}}\lesssim 10^{36}\mathrm{erg}{\mathrm{s}}^{-1}$), the accretion flow in the inner region around the NS is expected to be existed in the form of the hot accretion flow, e.g., the advection-dominated accretion flow (ADAF) as that in black hole X-ray binaries. Following our previous studies in Qiao $\&$ Liu 2020a and 2020b on the ADAF accretion around NSs, in this paper, we investigate the radiative efficiency of NSs with an ADAF accretion in detail, showing that the radiative efficiency of NSs with an ADAF accretion is much lower than that of $\epsilon \sim \frac{\dot{M}GM}{R_{\ast }}/\dot{M}{c}^2\sim 0.2$ despite the existence of the hard surface. As a result, given a X-ray luminosity $L_{\mathrm{X}}$ (e.g., between 0.5 and 10 keV), $\dot{M}$ calculated by $\dot{M}=L_{\mathrm{X}}\frac{R_{\ast }}{GM}$ is lower than the real $\dot{M}$ calculated within the framework of the ADAF accretion. The real $\dot{M}$ can be more than two orders of magnitude higher than that of calculated by $\dot{M}=L_{\mathrm{X}}\frac{R_{\ast }}{GM}$ with appropriate model parameters. Finally, we discuss that if applicable, the model of ADAF accretion around a NS can be applied to explain the observed millisecond X-ray pulsation in some NS-LMXBs (such as PSR J1023+0038, XSS J12270-4859 and IGR J17379-3747) at a lower X-ray luminosity of a few times of $10^{33}\mathrm{erg}{\mathrm{s}}^{-1}$, since at this X-ray luminosity the calculated $\dot{M}$ with the model of ADAF accretion can be high enough to drive a fraction of the matter in the accretion flow to be channelled onto the surface of the NS forming the X-ray pulsation.

arXiv comment9 pages, 5 figures, accepted for publication by MNRAS

References in corpus (37)

• Advection-Dominated Accretion: A Self-Similar Solution
• Advection-Dominated Accretion: Underfed Black Holes and Neutron Stars
• Hot Accretion Flows Around Black Holes
• Modelling the behaviour of accretion flows in X-ray binaries
• Magnetic Fields of Accreting X-Ray Pulsars with the Rossi X-Ray Timing Explorer
• On the Nature of the X-ray Emission from the Accreting Millisecond Pulsar SAX J1808.4-3658
• MHD simulations of accretion onto a dipolar magnetosphere. II. Magnetospheric ejections and stellar spin-down
• Spectrum of Optically Thin Advection Dominated Accretion Flow around a Black Hole: Application to Sgr A*
• Episodic Accretion on to Strongly Magnetic Stars
• Accretion to Magnetized Stars through the Rayleigh-Taylor Instability: Global Three-Dimensional Simulations
• Accretion Discs Trapped Near Corotation
• The Radiative Efficiency of Hot Accretion Flows
• "Propeller" Regime of Disk Accretion to Rapidly Rotating Stars
• Discovery of coherent millisecond X-ray pulsations in Aql X-1
• Propeller-driven Outflows and Disk Oscillations
• Thermonuclear X-ray bursts
• X-ray coherent pulsations during a sub-luminous accretion disk state of the transitional millisecond pulsar XSS J12270-4859
• Low-level accretion in neutron-star X-ray binaries
• Radio imaging observations of PSR J1023+0038 in an LMXB state
• Timing Observations of PSR J1023+0038 During a Low-Mass X-ray Binary State
• 1 Hz flaring in SAX J1808.4--3658: flow instabilities near the propeller stage
• RXTE Discovery of Multiple Cyclotron Lines during the 2004 December Outburst of V0332+53
• A Hard X-Ray Power-Law Spectral Cutoff in Centaurus X-4
• Self-Similar Hot Accretion Flow onto a Neutron Star
• Magnetic fields of neutron stars in X-ray binaries
• The Reflares and Outburst Evolution in the Accreting Millisecond Pulsar SAX J1808.4-3658: a Disk Truncated Near Co-rotation?
• The Radiative Efficiency of a Radiatively Inefficient Accretion Flow
• 1 Hz Flaring in the Accreting Millisecond Pulsar NGC 6440 X-2: Disk Trapping and Accretion Cycles
• Very hard states in neutron star low-mass X-ray binaries
• Suzaku X-Ray Study of an Anomalous Source XSS J12270-4859
• On the curious pulsation properties of the accreting millisecond pulsar IGR J17379-3747
• Unveiling the nature of compact object in the LMXB MAXI J1957+032 using Swift-XRT
• A systematic study of the advection-dominated accretion flow for the origin of the X-ray emission in weakly magnetized low-level accreting neutron star
• Boundary Layer Self-Similar Solution for the Hot Radiative Accretion onto a Rapidly Spinning Neutron Star
• The advection-dominated accretion flow for the origin of the thermal soft X-ray component in low-level accreting neutron stars
• A Study of Low-Mass X-Ray Binaries in the Low-Luminosity Regime
• The advection-dominated accretion flow for the anti-correlation between the X-ray photon index and the X-ray luminosity in neutron star low-mass X-ray binaries

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