Is Thermal Expansion Driving the Initial Gas Ejection in NGC 6251?

Abstract

In this paper, we explore the possibility that the radiative properties of the most compact region in NGC 6251* may be understood in the same sense as Sgr A*, though with some telling differences that may hint at the nature of jet formation. We show that observations of this object with ASCA, ROSAT, HST and VLBI together may be hinting at a picture in which Bondi-Hoyle accretion from an ambient ionized medium feeds a standard disk accreting at ~ 4.0*10^{22} g s^{-1}. Somewhere near the event horizon, this plasma is heated to >10^{11} K, where it radiates via thermal synchrotron (producing a radio component) and self-Comptonization (accounting for a nonthermal X-ray flux). This temperature is much greater than its virial value and the hot cloud expands at roughly the sound speed (~0.1c), after which it begins to accelerate on a parsec scale to relativistic velocities. In earlier work, the emission from the extended jet has been modeled successfully using nonthermal synchrotron self-Compton processes, with a self-absorbed inner core. In the picture we are developing here, the initial ejection of matter is associated with a self-absorbed thermal radio component that dominates the core emission on the smallest scales. The nonthermal particle distributions responsible for the emission in the extended jet are then presumably energized, e.g., via shock acceleration, within the expanding, hot gas. The power associated with this plasma represents an accretion efficiency of about 0.54, requiring dissipation in a prograde disk around a rapidly spinning black hole (with spin parameter a~1).

arXiv comment17 pages, 1 figures, to appear in Apj

References in corpus (17)

• Viewing the Shadow of the Black Hole at the Galactic Center
• The Supermassive Black Hole at the Galactic Center
• The Spectral Energy Distributions of Low-Luminosity Active Galactic Nuclei
• ASCA observations of Seyfert 1 galaxies: I. Data Analysis, Imaging and Timing
• Magnetic Stress at the Marginally Stable Orbit: Altered Disk Structure, Radiation, and Black Hole Spin Evolution
• Efficiency of Magnetized Thin Accretion Disks in the Kerr Metric
• The `quiescent' black hole in M87
• Magnetized Accretion Inside the Marginally Stable Orbit around a Black Hole
• Is the Accretion Flow in NGC 4258 Advection-dominated?
• Possible Evidence for Truncated Thin Disks in the Low-Luminosity Active Galactic Nuclei M81 and NGC 4579
• Hydrodynamical Accretion Onto Sgr A* From Distributed Point Sources
• Nuclear Disks of Gas and Dust in Early Type Galaxies and the Hunt for Massive Black Holes: Hubble Space Telescope Observations of NGC 6251
• Polarized mm And sub-mm Emission From Sgr A* At The Galactic Center
• Sub-parsec-scale Accleration of the Radio Jet in the Powerful Radio Galaxy NGC 6251
• Outflow Angles, Bulk Lorentz Factors, and Kinematics of Outflows from the Cores of AGN
• An Anomalous UV Extension in NGC6251
• Accretion Processes in the Nucleus of M31

Cited by in corpus (7)

• Magnetic Driving of Relativistic Outflows in Active Galactic Nuclei. I. Interpretation of Parsec-Scale Accelerations
• Relativistic Magnetohydrodynamics with Application to Gamma-Ray Burst Outflows: I. Theory and Semianalytic Trans-Alfvenic Solutions
• A synchrotron self-Compton scenario for the very high energy gamma-ray emission of the radiogalaxy M87
• A relativistic model of the radio jets in NGC 315
• The XMM-Newton view of NGC 6251
• Long-Term X-Ray monitoring of NGC6251: Evidence for a jet-dominated radio galaxy
• Shadowing of the Nascent Jet in NGC 4261 by a Line-Emitting Supersonic Accretion Disk