Electron Acceleration around the Supermassive Black Hole at the Galactic Center

By Siming Liu, V. Petrosian, F. Melia. 2001

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The recent detection of variable infrared emission from Sagittarius A* combined with its previously observed flare activity in X-rays provide compelling evidence that at least a portion of this object's emission is produced by nonthermal electrons. The polarization and variability of Sgr A*'s emission depend strongly on the observed wavelength, indicating distinct physical processes. We show here that acceleration of electrons by plasma wave turbulence in hot gases near the black hole's event horizon can, although with several theoretical uncertainties, reasonably account both for Sgr A*'s millimeter and shorter wavelength emission in the quiescent state and for the infrared and X-ray flares, induced either via an enhancement of the mass accretion rate onto the black hole or by reorganization of magnetic fields coupled to the accretion gas. High-energy electrons diffusing away from the acceleration site toward larger radii might account for Sgr A*'s emission at longer wavelengths. The acceleration model produces prominent IR flares accompanying X-ray bursts. Future coordinated multiwavelength observations will be able to test this model and constrain its parameters.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/d8bcb686ce093bedbfff4fb649e299827f6663da

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X-ray flares reveal mass and angular momentum of the Galactic Center black hole (2004, background): “For a brief overview see for instance Melia & Falcke (2001), Baganoff et al. (2001), Porquet et al. (2003) and Yuan et al. (2003).”
RADIATIVE MODELS OF SGR A* FROM GRMHD SIMULATIONS (2009, background): “…are (aside from the 230 GHz flux density) the submillimeter spectral slope α, the upper limit on the quiescent NIR flux density (Genzel et al. 2003; Melia & Falcke 2001; Hornstein et al. 2002; Schödel et al. 2007; Dodds-Eden et al. 2009), and the upper limit on the quiescent luminosity between 2…”
Two‐dimensional adiabatic flows on to a black hole – I. Fluid accretion (2003, background): “The epitome of an underfed black hole is the Galactic Centre (e.g. Melia & Falcke 2001).”
An X-Ray, Infrared, and Submillimeter Flare of Sagittarius A* (2007, background): “The radio, IR, and X-ray source Sagittarius A* is associated with a supermassive black hole at the center of our Galaxy (Melia & Falcke 2001).”
What drives the growth of black holes (2011, background): “However, with an estimated Eddington ratio of λ ≈ 10−8–1010 (e.g., Melia & Falcke, 2001; Eckart et al., 2006), Sgr A* is ≈ 5–8 orders of magnitude below the optically thick–optically thin accretion state and is only identifiable as “active” due to its proximity.”
Hard X-ray view of the past activity of Sgr A in a natural Compton mirror (2004, background): “It has remained puzzling why the source Sgr A⋆ associated with the BH is faint despite the presence of significant amounts of ambient gas capable of fuelling it (Melia & Falcke 2001; Baganoff et al. 2003).”
Stochastic Acceleration by Turbulence (2012, methodology): “But SA has been applied to nonthermal emission from accretion disks around black holes: e.g. Sgr A* black hole in the center of the milky way (Liu et al, 2004, 2006a and 2006b), other active galactic nuclei (Stawartz & Petrosian 2008), stellar size black holes (Li & Miller 1997), gamma-ray bursts…”
Chandra X-Ray Spectroscopic Imaging of Sagittarius A* and the Central Parsec of the Galaxy (2001, background): “Several papers in the literature have used the luminosity reported by Predehl & Zinnecker under the assumption that it was unabsorbed (e.g., Melia & Falcke 2001).”
The Stellar Cusp around the Supermassive Black Hole in the Galactic Center (2003, background): “Because of its proximity (distance 8 kpc; Reid 1993), the center of the Milky Way is a unique laboratory for studying the physical processes in galactic nuclei (e.g., Genzel, Hollenbach, & Townes 1994; Morris & Serabyn 1996; Mezger, Duschl, & Zylka 1996; Melia & Falcke 2001).”
Black Hole Parameter Estimation from Its Shadow (2018, background): “Astronomical observations suggest that each galaxy hosts millions of stellarmass black holes, and also a supermassive black hole at the nucleus of the galaxy (Melia & Falcke 2001; Shen et al. 2005).”
Coronal outflow dominated accretion discs: a new possibility for low-luminosity black holes? (2001, background): “…consistent with the polarization characteristics of SGR A∗ at millimeter and submillimeter wavelength, see Agol, 2000, Quataert & Gruzinov, 2000b, and Melia & Falcke, 2001, and references therein) may be due to the feedback from the coronal outflow suppressing the accretion rate at larger radii.”
A Fundamental plane of black hole activity (2003, neutral): “…(1995); (57) Turner & Pounds (1989); (58) Tadhunter et al. (2003); (59) Young et al. (2002); (60) Magorrian et al. (1998); (61) This work; (62) Melia & Falcke (2001); (63) Baganoff et al. (2001); (64) Schödel et al. (2002); (65) Orosz & Bailyn (1997); (66) Greiner, Cuby &…”
A Jet-ADAF model for Sgr A* (2001, methodology): “The energetic radio source Sgr A∗ located at the center of our Galaxy is now widely believed to be the signature of a massive black hole with mass M = 2.6× 106M⊙ (Melia & Falcke 2001; Haller et al. 1996; Eckart & Genzel 1996; Ghez et al. 1998; Reid et al. 1999; Backer & Sramek 1999).”
DISCOVERY OF A SUPERLUMINAL Fe K ECHO AT THE GALACTIC CENTER: THE GLORIOUS PAST OF Sgr A* PRESERVED BY MOLECULAR CLOUDS (2010, background): “Such a low luminosity is difficult to reconcile with the dense environment that is present in the center of the Galaxy and has motivated the development of several radiatively inefficient accretion/ejection models (Melia & Falcke 2001).”
Stellar Dynamics in the Central Arcsecond of Our Galaxy (2003, methodology): “Assuming a half-mass radius of rh 0:1 mas (Doeleman et al. 2001; Rogers et al. 1994; Melia & Falcke 2001), we obtain with the above mass estimates SgrA 7:5 103 M =2 4 =3ð Þr3h > 3 1019 M pc 3 : ð2Þ Figure 12 is a summary of the lower limits on the density of the central dark mass obtained by…”
Supermassive Black Holes in Galactic Nuclei: Past, Present and Future Research (2004, background): “An excellent review of the nature and observations of Sgr A∗ can be found in Melia & Falcke (2001), to which we refer the reader for a detailed discussion.”
Astrobiology: The Study of the Living Universe (2005, background): “Astrophysicists, after all, spent decades studying and searching for black holes before accumulating today’s compelling evidence that they exist (Melia & Falcke 2001).”
The structure of the nuclear stellar cluster of the Milky Way (2006, background): “Also, there a theoretical and observational arguments that favour the presence of a jet in Sgr A* (e.g., Melia & Falcke 2001; Markoff et al. 2001; Yuan et al. 2002; Bower et al. 2004).”