arXiv subjects

Mark W. Sincell

Publications and source records attributed to Mark W. Sincell.

4 recordsLinked to original sources

arXiv1998

Lyman Edge Features from Accretion Disks Around Maximally Rotating Supermassive Black Hole

We calculate the amplitude of the Lyman discontinuity for an accretion disk around a maximally rotating black hole. The locally emitted disk spectrum is computed with a previously developed numerical model (Sincell and Krolik 1998) and then a new general relativistic ray-tracing code is used to determine the observed spectra as a function of inclination angle, theta_o. We find that Lyman discontinuities are undetectable for disks viewed at inclinations cos(theta_o) < 0.8, but a significant feature remains for disks seen face-on.

astro-ph↗

arXiv1997

The Vertical Structure and Ultraviolet Spectrum of Accretion Disks Heated by Internal Dissipation in Active Galactic Nuclei

We present an improved calculation of the vertical structure and ultraviolet spectrum of a dissipative accretion disk in an AGN. We calculate model spectra in which the viscous stress is proportional to the total pressure, the gas pressure only and the geometric mean of the radiation and gas pressures (cf. Laor & Netzer 1989: LN89). As a result of a more complete treatment of absorptive opacity, we find greater overall spectral curvature than did LN89, as well as larger amplitudes in both the Lyman and HeII photoionization edges. The local black body approximation is not a good description of the near UV spectrum. With relativistic corrections (appropriate to non-rotating black holes) included, we find that the near UV spectrum hardens with increasing m-dot / m_8 (m-dot is the accretion rate in Eddington units, m_8 the black hole mass in units of 10^8 M_Sun). The near UV spectrum is consistent with observations if m-dot/ m_8 \sim 10^{-3}, but disks this cold would have large, and unobserved, absorption features at the Lyman edge. The edge amplitude is reduced when m-dot/m_8 is larger, but then the near-UV slope is too hard to match observations. We conclude that models in which conventional disks orbit non-rotating black holes do not adequately explain UV continuum production in AGN.

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arXiv1996

Multi-Wavelength Variability of the Synchrotron Self-Compton Model for Blazar Emission

Motivated by recent reports of strongly correlated radio and X-ray variability in 3C279 (Grandi, etal 1995), we have computed the relative amplitudes of variations in the synchrotron flux at $ν$ and the self-Compton X-ray flux at 1 keV ($R(ν)$) for a homogeneous sphere of relativistic electrons orbiting in a tangled magnetic field. Relative to synchrotron self-Compton scattering without induced Compton scattering, stimulated scattering reduces the amplitude of $R(ν)$ by as much as an order of magnitude when $τ_T \gtwid 1$. When $τ_T$ varies in a fixed magnetic field, $R_τ$ increases monotonically from 0.01 at $ν_o$, the self-absorption turnover frequency, to $0.5$ at $100 ν_o$. The relative amplitudes of the correlated fluctuations in the radio-mm and X-ray fluxes from 3C279 are consistent with the synchrotron self-Compton model if $τ_T$ varies in a fixed magnetic field and induced Compton scattering is the dominant source of radio opacity. The variation amplitudes are are too small to be produced by the passage of a shock through the synchrotron emission region unless the magnetic field is perpendicular to the shock front.

astro-ph↗

arXiv1996

The Vertical Structure and Ultraviolet Spectrum of X-Ray Irradiated Accretion Disks in Active Galactic Nuclei

Motivated by recent work indicating that the UV continuum in AGN may be produced by reradiation of energy absorbed from X-rays irradiating an accretion disk, we present a calculation of the vertical structures and ultraviolet spectra of X-ray irradiated accretion disks around massive non-rotating black holes. After finding the radial dependence of vertically-integrated quantities for these disks, we solve the equations of hydrostatic equilibrium, energy balance, and frequency-dependent radiation transfer as functions of altitude. To solve the last set of equations, we use a variable Eddington factor method. We include electron scattering, free-free, and HI, HeI, and HeII bound-free opacities and the corresponding continuum cooling processes. While the overall spectral shape predicted by X-ray irradiation may be compatible with observations, the Lyman edge emission feature it predicts is not. This finding raises questions for many otherwise plausible models in which X-ray irradiation plays a major role.

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