Period variations in pulsating X-ray sources. I. Accretion flow parameters and neutron star structure from timing observations

Journal Article · Fri Sep 15 00:00:00 EDT 1978 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/156446· OSTI ID:6879276

Lamb, F K; Pines, D; Shaham, J

We show that valuable information about both accretion flows and neutron star structure can be obtained from X-ray timing observations of period variations in pulsating sources. Such variations can result from variations in the accretion flow, or from internal torque variations, associated with oscillations of the fluid core or the unpinning of vortices in the inner crust. We develop a statistical description of torque variations in terms of noise processes, indicate how the applicability of such a description may be tested observationally, and show how it may be used to determine from observation both the properties of accretion flows and the internal structure of neutron stars, including the relative inertial moments of the crust and superfluid neutron core, the crust-core coupling time, and the frequencies of any low-frequency internal collective modes. Particular attention is paid to the physical origin of spin-down episodes; it is shown that usyc episodes may result either from external torque reversals or from internal torque variations.With the aid of the statistical description, the response of the star to torque fluctuations is calculated for three stellar models: (i) a completely rigid star; (ii) a two-component star; and (iii) a two-component star with a finite-frequency internal mode, such as the Tkachenko mode of a rotating neutron superfluid. Our calculations show that fluctuating torques could account for the period the period variations and spin-down episodes observed in Her X-1 and Cen X-3, including the large spin-down event observed in the latter source during 1972 September-October. The torque noise strengths inferred from current timing observations using the simple two-component models are shown to be consistent with those to be expected from fluctuations in accretion flows onto magnetic neutron stars.

• Research Organization: Department of Physics, University of Illinois at Urbana-Champaign
• OSTI ID: 6879276
• Journal Information: Astrophys. J.; (United States), Vol. 224:3
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
COSMIC X-RAY SOURCES
PULSATIONS
STAR MODELS
NEUTRON STARS
STAR ACCRETION
BINARY STARS
FLUCTUATIONS
PLASMA
PULSARS
ROTATION
SUPERFLUID MODEL
TORQUE
VARIATIONS
X RADIATION
COSMIC RADIO SOURCES
COSMIC RAY SOURCES
ELECTROMAGNETIC RADIATION
IONIZING RADIATIONS
MATHEMATICAL MODELS
MOTION
NUCLEAR MODELS
RADIATIONS
STAR EVOLUTION
STARS
640103* - Astrophysics & Cosmology- Quasi-Stellar
Radio
& X-Ray Sources- (-1987)