Relativistic iron emission lines in neutron star low-mass X-ray binaries as probes of neutron star radii

Abstract

Using Suzaku observations of three neutron star low-mass X-ray binaries (Ser X-1, 4U 1820-30 and GX 349+2) we have found broad, asymmetric, relativistic Fe K emission lines in all three objects. These Fe K lines can be well fit by a model for lines from a relativistic accretion disk ('diskline'), allowing a measurement of the inner radius of the accretion disk, and hence an upper limit on the neutron star radius. These upper limits correspond to 14.5 - 16.5 km for a 1.4 M(solar) neutron star. The inner disk radii we measure with Fe K lines are in good agreement with the inner disk radii implied by kHz QPOs observed in both 4U 1820-30 and GX 349+2, supporting the inner disk nature of kHz QPOs. Additionally, the Fe K lines observed in these neutron stars are narrower than those in the black holes that are thought to be close to maximally spinning, as one would expect if inferences for spin are robust.

6 pages, 3 figures, 3 tables, accepted to ApJ

References in corpus (11)

• Neutron Star Observations: Prognosis for Equation of State Constraints
• Constraining Black Hole Spin Via X-ray Spectroscopy
• Relativistic X-ray Lines from the Inner Accretion Disks Around Black Holes
• Constraints on the high-density nuclear equation of state from the phenomenology of compact stars and heavy-ion collisions
• Evaluating Spectral Models and the X-ray States of Neutron-Star X-ray Transients
• Magnetic Hydrogen Atmosphere Models and the Neutron Star RX J1856.5-3754
• Cooling of the quasi-persistent neutron star X-ray transients KS 1731-260 and MXB 1659-29
• Constraints on Neutron Star Properties from X-ray Observations of Millisecond Pulsars
• Evidence of a Broad Relativistic Iron Line from the Neutron Star Low-Mass X-ray Binary Serpens X-1
• On the maximum amplitude and coherence of the kilohertz quasi-periodic oscillations in low-mass X-ray binaries
• Non-Detection of Gravitationally Redshifted Absorption Lines in the X-ray Burst Spectra of GS 1826-24

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