A MODEL FOR THE WAVEFORM BEHAVIOR OF ACCRETING MILLISECOND X-RAY PULSARS: NEARLY ALIGNED MAGNETIC FIELDS AND MOVING EMISSION REGIONS

Journal Article · Fri Nov 20 00:00:00 EST 2009 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/706/1/417· OSTI ID:21378198

Lamb, Frederick K; Boutloukos, Stratos; Van Wassenhove, Sandor; Chamberlain, Robert T; Lo, Ka Ho; Clare, Alexander; Wenfei, Yu ^[1]

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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)

We investigate further a model of the accreting millisecond X-ray pulsars we proposed earlier. In this model, the X-ray-emitting regions of these pulsars are near their spin axes but move. This is to be expected if the magnetic poles of these stars are close to their spin axes, so that accreting gas is channeled there. As the accretion rate and the structure of the inner disk vary, gas is channeled along different field lines to different locations on the stellar surface, causing the X-ray-emitting areas to move. We show that this 'nearly aligned moving spot model' can explain many properties of the accreting millisecond X-ray pulsars, including their generally low oscillation amplitudes and nearly sinusoidal waveforms; the variability of their pulse amplitudes, shapes, and phases; the correlations in this variability; and the similarity of the accretion- and nuclear-powered pulse shapes and phases in some. It may also explain why accretion-powered millisecond pulsars are difficult to detect, why some are intermittent, and why all detected so far are transients. This model can be tested by comparing with observations the waveform changes it predicts, including the changes with accretion rate.

• OSTI ID: 21378198
• Journal Information: Astrophysical Journal, Vol. 706, Issue 1; Other Information: DOI: 10.1088/0004-637X/706/1/417; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
EMISSION
MAGNETIC FIELDS
NEUTRON STARS
OSCILLATIONS
PULSARS
PULSE SHAPERS
PULSES
ROTATION
SPIN
WAVE FORMS
X RADIATION
ANGULAR MOMENTUM
COSMIC RADIO SOURCES
ELECTROMAGNETIC RADIATION
ELECTRONIC CIRCUITS
IONIZING RADIATIONS
MOTION
PARTICLE PROPERTIES
PULSE CIRCUITS
RADIATIONS
SIGNAL CONDITIONERS
STARS