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Title: ORIGIN OF INTERMITTENT ACCRETION-POWERED X-RAY OSCILLATIONS IN NEUTRON STARS WITH MILLISECOND SPIN PERIODS

Abstract

We have shown previously that many of the properties of persistent accretion-powered millisecond pulsars can be understood if their X-ray emitting areas are near their spin axes and move as the accretion rate and structure of the inner disk vary. Here, we show that this 'nearly aligned moving spot model' may also explain the intermittent accretion-powered pulsations that have been detected in three weakly magnetic accreting neutron stars. We show that movement of the emitting area from very close to the spin axis to approx10 deg. away can increase the fractional rms amplitude from approx<0.5%, which is usually undetectable with current instruments, to a few percent, which is easily detectable. The second harmonic of the spin frequency usually would not be detected, in agreement with observations. The model produces intermittently detectable oscillations for a range of emitting area sizes and beaming patterns, stellar masses and radii, and viewing directions. Intermittent oscillations are more likely in stars that are more compact. In addition to explaining the sudden appearance of accretion-powered millisecond oscillations in some neutron stars with millisecond spin periods, the model explains why accretion-powered millisecond oscillations are relatively rare and predicts that the persistent accretion-powered millisecond oscillations of other starsmore » may become undetectable for brief intervals. It suggests why millisecond oscillations are frequently detected during the X-ray bursts of some neutron stars but not others and suggests mechanisms that could explain the occasional temporal association of intermittent accretion-powered oscillations with thermonuclear X-ray bursts.« less

Authors:
; ; ; ;  [1]
  1. Center for Theoretical Astrophysics and Department of Physics, University of Illinois at Urbana-Champaign, 1110 West Green Street, Urbana, IL 61801-3080 (United States)
Publication Date:
OSTI Identifier:
21378416
Resource Type:
Journal Article
Journal Name:
Astrophysical Journal (Online)
Additional Journal Information:
Journal Volume: 705; Journal Issue: 1; Other Information: DOI: 10.1088/0004-637X/705/1/L36; Journal ID: ISSN 1538-4357
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; NEUTRON STARS; OSCILLATIONS; PULSARS; PULSATIONS; ROTATION; SPIN; X RADIATION; ANGULAR MOMENTUM; COSMIC RADIO SOURCES; ELECTROMAGNETIC RADIATION; IONIZING RADIATIONS; MOTION; PARTICLE PROPERTIES; RADIATIONS; STARS

Citation Formats

Lamb, Frederick K, Boutloukos, Stratos, Van Wassenhove, Sandor, Chamberlain, Robert T, Lo, Ka Ho, and Coleman Miller, M., E-mail: fkl@illinois.ed. ORIGIN OF INTERMITTENT ACCRETION-POWERED X-RAY OSCILLATIONS IN NEUTRON STARS WITH MILLISECOND SPIN PERIODS. United States: N. p., 2009. Web. doi:10.1088/0004-637X/705/1/L36.
Lamb, Frederick K, Boutloukos, Stratos, Van Wassenhove, Sandor, Chamberlain, Robert T, Lo, Ka Ho, & Coleman Miller, M., E-mail: fkl@illinois.ed. ORIGIN OF INTERMITTENT ACCRETION-POWERED X-RAY OSCILLATIONS IN NEUTRON STARS WITH MILLISECOND SPIN PERIODS. United States. https://doi.org/10.1088/0004-637X/705/1/L36
Lamb, Frederick K, Boutloukos, Stratos, Van Wassenhove, Sandor, Chamberlain, Robert T, Lo, Ka Ho, and Coleman Miller, M., E-mail: fkl@illinois.ed. 2009. "ORIGIN OF INTERMITTENT ACCRETION-POWERED X-RAY OSCILLATIONS IN NEUTRON STARS WITH MILLISECOND SPIN PERIODS". United States. https://doi.org/10.1088/0004-637X/705/1/L36.
@article{osti_21378416,
title = {ORIGIN OF INTERMITTENT ACCRETION-POWERED X-RAY OSCILLATIONS IN NEUTRON STARS WITH MILLISECOND SPIN PERIODS},
author = {Lamb, Frederick K and Boutloukos, Stratos and Van Wassenhove, Sandor and Chamberlain, Robert T and Lo, Ka Ho and Coleman Miller, M., E-mail: fkl@illinois.ed},
abstractNote = {We have shown previously that many of the properties of persistent accretion-powered millisecond pulsars can be understood if their X-ray emitting areas are near their spin axes and move as the accretion rate and structure of the inner disk vary. Here, we show that this 'nearly aligned moving spot model' may also explain the intermittent accretion-powered pulsations that have been detected in three weakly magnetic accreting neutron stars. We show that movement of the emitting area from very close to the spin axis to approx10 deg. away can increase the fractional rms amplitude from approx<0.5%, which is usually undetectable with current instruments, to a few percent, which is easily detectable. The second harmonic of the spin frequency usually would not be detected, in agreement with observations. The model produces intermittently detectable oscillations for a range of emitting area sizes and beaming patterns, stellar masses and radii, and viewing directions. Intermittent oscillations are more likely in stars that are more compact. In addition to explaining the sudden appearance of accretion-powered millisecond oscillations in some neutron stars with millisecond spin periods, the model explains why accretion-powered millisecond oscillations are relatively rare and predicts that the persistent accretion-powered millisecond oscillations of other stars may become undetectable for brief intervals. It suggests why millisecond oscillations are frequently detected during the X-ray bursts of some neutron stars but not others and suggests mechanisms that could explain the occasional temporal association of intermittent accretion-powered oscillations with thermonuclear X-ray bursts.},
doi = {10.1088/0004-637X/705/1/L36},
url = {https://www.osti.gov/biblio/21378416}, journal = {Astrophysical Journal (Online)},
issn = {1538-4357},
number = 1,
volume = 705,
place = {United States},
year = {Sun Nov 01 00:00:00 EDT 2009},
month = {Sun Nov 01 00:00:00 EDT 2009}
}