5 research outputs found
Asymmetry in the Spectrum of High-Velocity H2O Maser Emission Features in Active Galactic Nuclei
We suggest a mechanism for the amplification of high-velocity water-vapor
maser emission features from the central regions of active galactic nuclei. The
model of an emitting accretion disk is considered. The high-velocity emission
features originate in the right and left wings of the Keplerian disk. The
hyperfine splitting of the signal levels leads to an asymmetry in the spectral
profile of the water vapor maser line at a frequency of 22.235 GHz. We show
that the gain profile asymmetry must lead to an enhanced brightness of the
blueshifted high-velocity emission features compared to the redshifted ones.
Such a situation is observed in the source UGC 3789.Comment: 11 pages 3 figure
Spread of Matter over a Neutron-Star Surface During Disk Accretion: Deceleration of Rapid Rotation
The problem of disk accretion onto the surface of a neutron star with a weak
magnetic field at a luminosity exceeding several percent of Eddington is
reduced to the problem of the braking of a hypersonic flow with a velocity that
is 0.4-0.5 of the speed of light above the base of the spreading layer -- a
dense atmosphere made up of previously fallen matter. We show that turbulent
braking in the Prandtl-Karman model with universally accepted coefficients for
terrestrial conditions and laboratory experiments and a ladder of interacting
gravity waves in a stratified quasi-exponential atmosphere at standard
Richardson numbers lead to a spin-up of the massive zone that extends to the
ocean made up of a plasma with degenerate electrons. Turbulent braking in the
ocean at the boundary with the outer solid crust reduces the rotation velocity
to the solid-body rotation velocity of the star. This situation should lead to
strong heating of deep atmospheric layers and to the switch-off of the
explosive helium burning mechanism. Obviously, a more efficient mechanism for
the dissipation of a fast azimuthal flow in the atmosphere should operate in
X-ray bursters. We show that a giant solitary gravity wave in the atmosphere
can lead to energy dissipation and to a sharp decrease in azimuthal velocity in
fairly rarefied atmospheric layers above the zone of explosive helium burning
nuclear reactions. We discuss the reasons why this wave, that has no direct
analog in the Earth's atmosphere or ocean, appears and its stability. We pose
the question as to whether neutron stars with massive atmospheres, spun up to
high velocities by accreting matter from a disk, can exist among the observed
Galactic X-ray sources.Comment: 12 pages, 12 figure
The λ0 λ0 =1.35 cm H2O Maser Line: The Hyperfine Structure and Profile Asymmetry
Abstract—The spectra of several H2O maser sources exhibit single λ0 =1.35 cm maser lines with narrow asymmetric profiles. We consider the hyperfine structure of the line that corresponds to the transition between the rotational 616 → 523 levels of ortho-H2O molecules to account for the line asymmetry. Our numerical simulations of the maser line profile agree well with the observations if the hyperfine structure is taken into account. PACS numbers: 98.58.Ec DOI:10.1134/S1063773706010051 Key words: hyperfine structure, spectral profile, maser emission