The impact of neutron star spin on X-ray spectra

Abstract

We investigate whether the intrinsic spin of neutron stars leaves an observable imprint on the spectral properties of X-ray binaries. To evaluate this we consider a sample of nine NSs for which the spins have been measured that are not accreting pulsars (for which the accretion geometry will be different). For each source, we perform spectroscopy on a majority of RXTE hard state observations. Our sample of sources and observations spans the range of the Eddington ratios Lx/Ledd ~0.005-0.100. We find a clear trend between key Comptonization properties and the NS spin for a given accretion rate. Specifically, at a given Lx/Ledd, for more rapidly rotating NSs we find lower seed photon temperatures and a general increase in Comptonization strength, as parametrised by the Comptonization y parameter and amplification factor A. This is in good agreement with the theoretical scenario whereby less energy is liberated in a boundary layer for more rapidly spinning NSs, resulting in a lower seed photon luminosity and, consequently, less Compton cooling in the corona. This effect in extremis results in the hard states of the most rapidly spinning sources encroaching upon the regime of Comptonization properties occupied by BHs.

arXiv comment11 pages, 5 figures, 3 tables. Accepted for publication in MNRAS

References in corpus (47)

• The Leiden/Argentine/Bonn (LAB) Survey of Galactic HI: Final data release of the combined LDS and IAR surveys with improved stray-radiation corrections
• MultiNest: an efficient and robust Bayesian inference tool for cosmology and particle physics
• X-ray spectral modelling of the AGN obscuring region in the CDFS: Bayesian model selection and catalogue
• Modelling the behaviour of accretion flows in X-ray binaries
• Thermonuclear (type-I) X-ray bursts observed by the Rossi X-ray Timing Explorer
• Millisecond Oscillations in X-Ray Binaries
• Gravitational Radiation and Rotation of Accreting Neutron Stars
• Sonic-Point Model of Kilohertz Quasi-Periodic Brightness Oscillations in Low-Mass X-ray Binaries
• kHz Quasi Periodic Oscillations in Low Mass X-ray Binaries as Probes of General Relativity in the Strong Field Regime
• Nuclear-Powered Millisecond Pulsars and the Maximum Spin Frequency of Neutron Stars
• Discovery of Sub-Millisecond Quasi-Periodic Oscillations in the X-Ray Flux of Scorpius X-1
• Thermonuclear burst oscillations
• Accretion Disk Boundary Layers Around Neutron Stars: X-ray Production in Low-Mass X-ray Binaries
• Boundary layer, accretion disk and X-ray variability in luminous LMXBs
• Dependence of the Frequency of the Kilohertz Quasi-Periodic Oscillations on X-ray Count Rate and Colors in 4U 1608-52
• Evidence for a 2:3 resonance in Sco X-1 kHz QPOs
• X-ray Bursts from the Accreting Millisecond Pulsar XTE J1814-338
• Periodic Thermonuclear X-ray Bursts from GS 1826-24 and the Fuel Composition as a Function of Accretion Rate
• Milli-second Oscillations in the Persistent and Bursting Flux of Aql X-1 During an Outburst
• The broad band X-ray/hard X-ray spectra of accreting neutron stars
• Spread of Matter over a Neutron-Star Surface During Disk Accretion: Deceleration of Rapid Rotation
• Spectra of the spreading layers on the neutron star surface and constraints on the neutron star equation of state
• Observational Constraints on Neutron Star Masses and Radii
• Modelling the spin equilibrium of neutron stars in LMXBs without gravitational radiation
• Changing Frequency Separation of Kilohertz Quasi-Periodic Oscillations in the Sonic-Point Beat-Frequency Model
• Millisecond Oscillations and Photospheric Radius Expansion in Thermonuclear X-Ray Bursts
• Boundary layer emission and Z-track in the color-color diagram of luminous LMXBs
• What ignites on the neutron star of 4U 0614+091?
• The MHD Alfven wave oscillation model of kHz Quasi Periodic Oscillations of Accreting X-ray Binaries
• On the high coherence of kilo-Hz Quasi-Periodic Oscillations
• Gravitational waves from Sco X-1: A comparison of search methods and prospects for detection with advanced detectors
• Energy Release During Disk Accretion onto a Rapidly Rotating Neutron Star
• Turbulent Mixing in the Surface Layers of Accreting Neutron Stars
• A dichotomy between the hard state spectral properties of black hole and neutron star X-ray~binaries
• An Empirical Method for Improving the Quality of RXTE PCA Spectra
• Chandra and RXTE Spectra of the Burster GS 1826-238
• Discovery of the Spin Frequency of 4U 0614+09 with SWIFT/BAT
• The Effect of Neutron Star Rotation on the Properties of Thermonuclear X-ray Bursts
• Discovery of Kilohertz QPOs in the Atoll X-Ray Binary 4U 1705-44
• Distribution of the Galactic Bulge emission at |b|>2deg according to the RXTE Galactic Center scans
• A Soft X-Ray Spectral Episode for the Clocked Burster, GS 1826-24 as Measured by Swift and NuSTAR
• Gravitational excitation of high frequency QPOs
• A new bursting X-ray transient: SAX J1750.8-2900
• Models of Quasi-Periodic Variability in Neutron Stars and Black Holes
• XMM-Newton Finds That SAX J1750.8-2900 May Harbor the Hottest, Most Luminous Known Neutron Star
• Spectral Softening Between Outburst and Quiescence In The Neutron Star Low-Mass X-Ray Binary SAX J1750.8-2900
• Statistical properties of twin kHz QPO in neutron star LMXBs

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• A model for the radio/X-ray correlation in three neutron star low-mass X-ray binaries 4U 1728-34, Aql X-1 and EXO 1745-248
• Evolution of the disc atmosphere in the X-ray binary MXB 1659-298, during its 2015-2017 outburst
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• Two-temperature radiative hot accretion flow around neutron stars
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