Achievements & Publications

Microlens diagnostics of accretion disks in active galactic nuclei

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Yonehara, A.,   Mineshige, S.,   Fukue, J.,   Umemura, M.,   Turner, E.~L.

The optical-ultraviolet continuum from active galactic nuclei (AGN) seems to originate from optically thick and/or thin disks, and occasionally from associated circumnuclear starburst regions. These different possible origins can, in principle, be distinguished by observations of gravitational microlensing events. We performed numerical simulations of microlensing of an AGN disk by...

AGN activity triggered by circumnuclear starbursts

Image

Umemura, Masayuki,   Fukue, Jun,   Mineshige, Shin

We present a radiative/hydrodynamical mechanism for triggering AGN activity; the intensive radiation from a circumnuclear starburst drives the nuclear fueling due to the Poynting-Robertson (radiation drag) effects. When the starburst is in an early and therefore super-Eddington phase, the radiative flux force is likely to obstruct severely the mass accretion...

Hydrodynamical evolution of AGN driven by radiation from circumnuclear starbursts

Image

Ohsuga, Ken,   Umemura, Masayuki,   Fukue, Jun,   Mineshige, Shin

We explore the hydrodynamical evolution of dusty gas around active galactic nuclei (AGN) driven by the radiation from circumnuclear starbursts. For this purpose, we calculate the temporal equilibrium states between the radiation force by starburst regions and the gravity in galactic nuclei. As a result, we find that the equilibrium...

Radiatively driven mass accretion on to galactic nuclei by circumnuclear starbursts

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Umemura, Masayuki,   Fukue, Jun,   Mineshige, Shin

We examine the physical processes of radiatively driven mass accretion on to galactic nuclei, owing to intensive radiation from circumnuclear starbursts. The radiation from a starburst not only causes the inner gas disc to contract via radition flux force, but also extracts angular momentum owing to relativistic radiation drag, thereby...

Optical Variability in Active Galactic Nuclei: Starbursts or Disk Instabilities?

Image

Kawaguchi, T.,   Mineshige, S.,   Umemura, M.,   Turner, Edwin L.

Aperiodic optical variability is a common property of active galactic nuclei (AGNs), though its physical origin is still open to question. To study the origin of the optical-ultraviolet variability in AGNs, we compare light curves of two models to observations of quasar 0957+561 in terms of a structure function analysis....

An X-Ray Microlensing Test of AU-Scale Accretion Disk Structure in Q2237+0305

Image

Yonehara, Atsunori,   Mineshige, Shin,   Manmoto, Tadahiro,   Fukue, Jun,   Umemura, Masayuki,   Turner, Edwin L.

The innermost regions of quasars can be resolved by a gravitational lens ``telescope`` on scales down to a few AU. For this purpose, X-ray observations are most preferable because X-rays originating from the innermost regions can be selectively amplified by microlensing resulting from the ``caustic crossing.'' If detected, X-ray variations...

A Criterion for Photoionization of Pregalactic Clouds Exposed to Diffuse Ultraviolet Background Radiation

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Tajiri, Yukiko,   Umemura, Masayuki

To elucidate the permeation of cosmic ultraviolet (UV) background radiation into a pregalactic cloud and the subsequent ionization, the frequency-dependent radiative transfer equation is solved, coupled with the ionization process, for a spherical top-hat cloud composed of pure hydrogen. The calculations properly involve scattering processes of ionizing photons that originate...

Image

Microlens diagnostics of accretion disks in active galactic nuclei

Yonehara, A.,   Mineshige, S.,   Fukue, J.,   Umemura, M.,   Turner, E.~L.

The optical-ultraviolet continuum from active galactic nuclei (AGN) seems to originate from optically thick and/or thin disks, and occasionally from associated circumnuclear starburst regions. These different possible origins can, in principle, be distinguished by observations of gravitational microlensing events. We performed numerical simulations of microlensing of an AGN disk by...

March 1999  
Image

AGN activity triggered by circumnuclear starbursts

Umemura, Masayuki,   Fukue, Jun,   Mineshige, Shin

We present a radiative/hydrodynamical mechanism for triggering AGN activity; the intensive radiation from a circumnuclear starburst drives the nuclear fueling due to the Poynting-Robertson (radiation drag) effects. When the starburst is in an early and therefore super-Eddington phase, the radiative flux force is likely to obstruct severely the mass accretion...

January 1999  
Image

Hydrodynamical evolution of AGN driven by radiation from circumnuclear starbursts

Ohsuga, Ken,   Umemura, Masayuki,   Fukue, Jun,   Mineshige, Shin

We explore the hydrodynamical evolution of dusty gas around active galactic nuclei (AGN) driven by the radiation from circumnuclear starbursts. For this purpose, we calculate the temporal equilibrium states between the radiation force by starburst regions and the gravity in galactic nuclei. As a result, we find that the equilibrium...

January 1999  
Image

Radiatively driven mass accretion on to galactic nuclei by circumnuclear starbursts

Umemura, Masayuki,   Fukue, Jun,   Mineshige, Shin

We examine the physical processes of radiatively driven mass accretion on to galactic nuclei, owing to intensive radiation from circumnuclear starbursts. The radiation from a starburst not only causes the inner gas disc to contract via radition flux force, but also extracts angular momentum owing to relativistic radiation drag, thereby...

October 1998   Monthly Notices of the Royal Astronomical Society
Image

Optical Variability in Active Galactic Nuclei: Starbursts or Disk Instabilities?

Kawaguchi, T.,   Mineshige, S.,   Umemura, M.,   Turner, Edwin L.

Aperiodic optical variability is a common property of active galactic nuclei (AGNs), though its physical origin is still open to question. To study the origin of the optical-ultraviolet variability in AGNs, we compare light curves of two models to observations of quasar 0957+561 in terms of a structure function analysis....

September 1998   The Astrophysical Journal
Image

An X-Ray Microlensing Test of AU-Scale Accretion Disk Structure in Q2237+0305

Yonehara, Atsunori,   Mineshige, Shin,   Manmoto, Tadahiro,   Fukue, Jun,   Umemura, Masayuki,   Turner, Edwin L.

The innermost regions of quasars can be resolved by a gravitational lens ``telescope`` on scales down to a few AU. For this purpose, X-ray observations are most preferable because X-rays originating from the innermost regions can be selectively amplified by microlensing resulting from the ``caustic crossing.'' If detected, X-ray variations...

July 1998   The Astrophysical Journal Letters
Image

A Criterion for Photoionization of Pregalactic Clouds Exposed to Diffuse Ultraviolet Background Radiation

Tajiri, Yukiko,   Umemura, Masayuki

To elucidate the permeation of cosmic ultraviolet (UV) background radiation into a pregalactic cloud and the subsequent ionization, the frequency-dependent radiative transfer equation is solved, coupled with the ionization process, for a spherical top-hat cloud composed of pure hydrogen. The calculations properly involve scattering processes of ionizing photons that originate...

July 1998   The Astrophysical Journal