Accretion Processes in the Nucleus of M31

Liu, Siming; Melia, Fulvio

doi:10.1086/319643

Cited by 4 publications

(1 citation statement)

References 31 publications

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“…The three Local Group galaxies with detected black holes serve as important laboratories for studying nuclear activity. The Galactic Center source Sgr A * and the nucleus of M31 both emit very weak, but detectable, nonstellar radiation in the radio and X-ray bands, considerations of which have led to new insights on accretion physics (Melia & Falcke 2001, and references therein;Liu & Melia 2001). In this regard, M32 has remained stubbornly elusive.…”

Section: Introductionmentioning

confidence: 99%

Detection of the “Active” Nucleus of M32

Terashima

Ulvestad

2003

ApJ

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M32 hosts a 2.5×10 6 M ⊙ central black hole, but signs of nuclear activity in this galaxy have long eluded detection. We report the first conclusive detection of the nucleus of M32 in X-rays, based on high-resolution, sensitive observations made with Chandra. The 2-10 keV luminosity is merely 9.4×10 35 erg s −1 , ∼ 3 × 10 −9 of the Eddington luminosity of the black hole. Weak diffuse emission, consistent with thermal gas at a temperature of 0.37 keV, is seen in an annular region ∼100 pc from the center. We also present a deep, moderately high-resolution (0. ′′ 9), radio continuum observation obtained with the Very Large Array, which places a tight upper bound on the nuclear radio power at 8.4 GHz. We combine these new measurements with upper limits at other wavelengths to discuss implications for the nature of accretion onto the central black hole.

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Section: Introductionmentioning

confidence: 99%

Detection of the “Active” Nucleus of M32

Terashima

Ulvestad

2003

ApJ

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Line Emission from Cooling Accretion Flows in the Nucleus of M31

Liu

Fromerth

Melia

2002

ApJ

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The recent Chandra X-ray observations of the nucleus of M31, combined with earlier VLA radio and HST UV spectral measurements, provide the strictest constraints on the nature of accretion onto the supermassive black hole (called M31* hereafter) in this region. One of the two newly-detected sources within roughly an arcsec of M31* may be its X-ray counterpart. If not, the X-ray flux from the nucleus must be even lower than inferred previously. Some uncertainty remains regarding the origin of the UV excess from the compact component known as P2. In our earlier analysis, we developed a unified picture for the broadband spectrum of this source. Contrary to the `standard' picture in which the infalling plasma attains temperatures in excess of 10^{10} K near the event horizon, the best fit model for M31*, under the assumption that the UV radiation is in fact produced by this source, appears to correspond to a cool branch solution, arising from strong line cooling inside the capture radius. Starting its infall with a temperature of about 10^6 K in the post-shock region, the plasma cools down efficiently to about 10^4 K toward smaller radii. An important prediction of this model is the appearance of a prominent UV spike from hydrogen line emission. In this paper we model this line emission with significantly greater accuracy, using the algorithm CLOUDY, and to correctly take into account the attenuation along the line of sight. We predict a spectrum with several additional prominent emission lines that can be used to verify the model with future high-resolution observations.Comment: 27 pages, 8 figure

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

Melia

Liu

Fatuzzo

2002

ApJ

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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).Comment: 17 pages, 1 figures, to appear in Ap

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Accretion Processes in the Nucleus of M31

Cited by 4 publications

References 31 publications

Detection of the “Active” Nucleus of M32

Detection of the “Active” Nucleus of M32

Line Emission from Cooling Accretion Flows in the Nucleus of M31

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

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