High Energy Astrophysics at Penn State : Active Galactic Nucleii ( AGN )

Penn State Dept. of Astronomy & Astrophysics

Active Galactic Nuclei Members of the Penn State X-ray Astronomy group are involved in both X-ray and optical studies of the supermassive black holes that reside in the nuclei of active galaxies. Gas accreting onto a black hole through an accretion disk emits an incredible amount of X-ray and optical emission, and spectral/variability studies of this emission reveal the physical conditions in the immediate vicinity of the black hole. Jets can also be fired out from the black hole region at nearly the speed of light. More info is available on AGN at the following sites:

ASCA, ROSAT, RXTE and SAX are the main satellite missions currently providing new X-ray results on active galaxies. Even larger advances will soon be possible with the launches of AXAF in 1998, XMM in 1999 and ASTRO-E in 2000. The vastly increased spectral resolution and collecting area provided by these satellites will revolutionize our understanding of the X-ray emitting regions around the black hole.

The Hobby-Eberly Telescope (HET), with its large collecting area and advanced focal plane instrumentation, will soon allow excellent optical/near-infrared spectroscopy of AGN. Queue scheduling of the HET will facilitate near-simultaneous observations with space-based observatories, rapid observations of variable AGN, and long-term AGN monitoring programs.

Current AGN research efforts at Penn State include studies of Narrow-Line Seyfert 1 Galaxies (Prof. Niel Brandt); AGN with double-peaked optical emission lines (Prof. Mike Eracleous); blazars (Prof. Eric Feigelson, Dr. Rita Sambruna and Dr. Joe Pesce); and Seyfert 2 galaxies (Dr. Rita Sambruna and Prof. Niel Brandt). See our list of publications for details on their work.

Narrow-Line Seyfert 1 Galaxies show extremely strong soft X-ray emission which is thought to originate in the innermost accretion disk. They also have remarkable optical emission line properties, hard X-ray spectra, and X-ray variability properties. It is likely that Narrow-Line Seyfert 1s have extreme values of a primary physical parameter such as mass accretion rate onto the black hole.

Double-peaked optical emission lines are found in about 10 per cent of radio-loud AGN. These AGN may be a small but distinct subclass which show broad optical line emission from an accretion disk. Tests are underway to determine if the double-peaked emission lines indeed arise from an accretion disk.

Blazars show highly nonthermal emission at a variety of wavelengths. This originates when a jet from an AGN is fired nearly along our line of sight. Blazars show strong variability and are often detected at extremely high X-ray and gamma-ray energies.

Seyfert 2 galaxies have their black hole regions hidden from direct sight by obscuring gas thought to be in the form of a torus. They can show strong emission lines at X-ray wavelengths, and the AXAF gratings should allow excellent spectroscopy of some of the brightest Seyfert 2s.

Spectrum of Seyvert Galaxy Black Hole Region

Web page by John A. Nousek(nousek@astro.psu.edu).

Penn State's High Energy Astrophysics group web pages are maintained by Scott Koch.
Last update: February 17, 1998