Low-luminosity accretion onto magnetized neutron stars

Journal Article · Tue Jun 15 04:00:00 EDT 1982 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/160028· OSTI ID:6940029

Langer, S H; Rappaport, S

We have studied the behavior of matter accreting at low rates (M<10/sup 16/ g s/sup -1/) onto the polar caps of a highly magnetized (Bapprox.10/sup 12/ gauss) neutron star. We have found flow solutions for the case in which the matter undergoes a stationary, collisionless shock. The electron and ion fluids are treated separately, and the ion temperature is found to be much higher than the electron temperature throughout the flow. At these low accretion rates, the emitted radiation is assumed to exert no significant pressure on the infalling matter and is further assumed to escape from the column without significant degradation in energy. We find that cyclotron emission is the dominant energy loss mechanism and yield continuum spectra resembling those observed from X-ray pulsars. From the model, we compute a number of relations among the accretion rate, the surface magnetic field, the shock height, and the characteristic electron and ion temperatures. For magnetic fields > or =10/sup 12/ gauss, typical values of kT/sub e/ are several times the cyclotron energy at the surface of the neutron star. When the magnetic field drops below approx.10/sup 12/ gauss, the electrons become very hot and emit ..gamma..-rays. The self-consistency of our assumptions and results are discussed in detail. Finally, we show how, in the next generation of such calculations, the radiation pressure can be coupled to the hydrodynamic equations.

• Research Organization: Joint Institute for Laboratory Astrophysics, University of Colorado and National Bureau of Standards
• OSTI ID: 6940029
• Journal Information: Astrophys. J.; (United States), Journal Name: Astrophys. J.; (United States) Vol. 257:2; ISSN ASJOA
• Country of Publication: United States
• Language: English

Related Subjects

640102* -- Astrophysics &amp; Cosmology-- Stars &amp; Quasi-Stellar
Radio &amp; X-Ray Sources
71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
BINARY STARS
BREMSSTRAHLUNG
COSMIC RAY SOURCES
COSMIC X-RAY SOURCES
CYCLOTRON RADIATION
ELECTROMAGNETIC RADIATION
ENERGY SPECTRA
FLUID FLOW
FLUID MECHANICS
HYDRODYNAMICS
MAGNETIC FIELDS
MAGNETIC STARS
MATHEMATICAL MODELS
MECHANICS
NEUTRON STARS
NUMERICAL SOLUTION
PLASMA
RADIATIONS
SHOCK WAVES
SPECTRA
STAR ACCRETION
STAR EVOLUTION
STAR MODELS
STARS