Kaiyou Chen

Kinematic evidence for a relativistic Keplerian disk - Arp 102B

Line profiles were calculated for a Keplerian disk with allowance made for relativistic effects. Excellent agreement was found between the resulting double peaked asymmetric profiles and the H-alpha line of Arp 102B; this yielded an accurate determination of several disk parameters. It is believed that the line profile of Arp 102B shows the most convincing direct kinematic evidence for rotation in any AGN. 39 refs.

Structure of line-emitting accretion disks in active galactic nuclei - Arp 102B

The prime objects of the present self-consistent model of a line-emitting accretion disk able to account for the properties observed in a small class of AGNs are Arp 102B and 3C 390.3, whose double-peaked emission lines have been attributed to a Keplerian disk. Improved calculations of the line profile of a relativistic Keplerian disk, generalized to include a variety of emissivity laws as well as local broadening due to electron scattering or turbulence, are noted to fit Arp 102B; analytic and numerical calculations of the solid angle presented by the outer thin disk to an extended isotropic source of illumination demonstrate that the energy budget requirements for line emission from the disk are also satisfied. 27 refs.

Line Emission from an Accretion Disk around a Rotating Black Hole: Toward a Measurement of Frame Dragging

Line emission from an accretion disk and a corotating hot spot about a rotating black hole are considered for possible signatures of the frame-dragging effect. We explicitly compare integrated line profiles from a geometrically thin disk about a Schwarzschild and an extreme Kerr black hole, and show that the line profile differences are small if the inner radius of the disk is near or above the Schwarzschild stable-orbit limit of radius 6GM/c2. However, if the inner disk radius extends below this limit, as is possible in the extreme Kerr spacetime, then differences can become significant, especially if the disk emissivity is stronger near the inner regions. We demonstrate that the first three moments of a line profile define a three-dimensional space in which the presence of material at small radii becomes quantitatively evident in broad classes of disk models. In the context of the simple, thin disk paradigm, this moment-mapping scheme suggests formally that the iron line detected by the Advanced Satellite for Cosmology and Astrophysics mission from MCG -6-30-15 (Tanaka et al.) is ~3 times more likely to originate from a disk about a rotating black hole than from a Schwarzschild system. A statistically significant detection of black hole rotation in this way may be achieved after only modest improvements in the quality of data. We also consider light curves and frequency shifts in line emission as a function of time for corotating hot spots in extreme Kerr and Schwarzschild geometries. The frequency-shift profile is a valuable measure of orbital parameters and might possibly be used to detect frame dragging even at radii approaching 6GM/c2 if the inclination angle of the orbital plane is large. The light curve from a hot spot shows differences as well, although these too are pronounced only at large inclination angles.

Optical pulse polarization of the Crab pulsar

The strong optical emission of the Crab pulsar allows us to study the polarization properties in detail. Optical pulsed emission can best be understood as synchrotron radiation of relativistic electron-positron pairs in the outer magnetosphere. We calculate the polarization properties of the optical pulses based on the outer gap model, which has explained much of the observed properties of this pulsar. We find that the calculated polarization profiles exhibit the same qualitative behaviors as the observations for a large range in parameter space. It seems that the optical polarizations do not constrain strongly on the Crab pulsar{close_quote}s emission geometry. {copyright} {ital 1996 The American Astronomical Society.}

Spectropolarimetric test of the relativistic disk model for the broad emission lines of active galactic nuclei

Previously, it was claimed that the broad emission lines of the radio galaxy Arp 102B can be fitted by the line profile from a simple relativistic Keplerian thin disk. It was argued that the lines originating from the relativistic accretion disk could be polarized due to electron scattering, which is likely to be the dominant opacity in the line-emitting region of Arp 102B. In the present work, the expected polarization properties of these broad emission lines are calculated. The percentage of polarization depends strongly on the inclination angle. For some angles, the red peak of the polarized, double-peaked line profile can be higher than the blue peak. This is in contrast to the total line profile, in which the blue peak is always higher than the red one. Spectropolarimetric observations could, therefore, provide an independent test of the relativistic disk model for the broad emission lines of Arp 102B and other active galactic nuclei. 25 refs.

Spectral studies of magnetic photon splitting in the March 5 event and SGR 1806−20

Soft Gamma Repeaters (SGRs) have been proposed to be neutron stars with extremely strong magnetic fields of ≳5×1014 G. The spectra of SGR 1806−20 and the initial spike of the March 5 event can be fitted by a photon-splitting modified spectrum under such a strong magnetic field. A moderate beaming pattern is needed for the emission producing the initial spike of the March 5 event, and the strength of its magnetic field is not well constrained by spectral fitting. An extended emission region over the whole stellar surface is preferred for SGR 1806−20 rather than a localized equatorial region. The intrinsic emission of SGR 1806−20 should be nearly isotropic. The magnetic field near the surface of SGR 1806−20 should be >10 Bc (Bc=4.4×1013 G) and its GM/c2R is ≳0.25.