On the Nature of the Variable Infrared Emission from Sagittarius A*

By F. Yuan, E. Quataert, Ramesh Narayan. 2004

151 citations recorded by the source corpus.

Recent infrared (IR) observations of the center of our Galaxy indicate that the supermassive black hole (SMBH) source Sgr A* is strongly variable in the IR. The timescale for the variability, ~30 minutes, is comparable to that of the X-ray flares observed by Chandra and XMM-Newton, suggesting a common physical origin. In this paper, we investigate the nature of the IR emission in the context of models recently proposed to interpret the X-ray flares. We show that the IR emission in Sgr A* can be well explained by nonthermal synchrotron emission if a small fraction of the electrons in the innermost region of the accretion flow around the black hole are accelerated into a broken power-law distribution, perhaps through transient events such as magnetic reconnection. The model predicts differences in the variability amplitudes of flares in the IR and X-rays, in general agreement with observations. It also predicts that the IR emission should be linearly polarized, as has indeed been observed during one epoch. IR and X-ray flares analogous to those observed in Sgr A* may be detectable from other accreting SMBHs, provided L ≲ 10-8LEdd; at higher luminosities, the flaring emission is dominated by thermal synchrotron self-Compton emission, which is likely to be less variable.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/c00c33a7c8f6ed1743ed0be49cc5cdd16af9d96f

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In Astronomy and Astrophysics

1. R. Genzel
2. T. Johannsen
3. T. Alexander
4. Ramesh Narayan
5. F. Eisenhauer
6. T. Ott
7. A. Eckart
8. A. Ghez

Citations in the corpus

• Detection of orbital motions near the last stable circular orbit of the massive black hole SgrA* (2018, background): “…in a hot, magnetized accretion disk/torus of ∼10 light minutes in diameter, plus perhaps a jet, just outside the innermost stable circular orbit (ISCO) of the putative massive black hole (Witzel et al. 2018; Johnson et al. 2018; Doeleman et al. 2008; Yuan et al. 2004; Markoff et al. 2001).”
• SINFONI in the Galactic Center: Young Stars and Infrared Flares in the Central Light-Month (2005, background): “Theoretical models predict that the infrared emission comes from a small fraction (a few percent) of the electrons near the event horizon that are accelerated to 103 in a nonthermal distribution and radiate in the near-infrared via synchrotron emission (Yuan et al. 2004).”
• An X-Ray, Infrared, and Submillimeter Flare of Sagittarius A* (2007, background): “Models for the flares have considered various mechanisms for injecting energy into the electrons, including stochastic acceleration, shocks, and magnetic reconnection (e.g. Markoff et al. 2001; Yuan et al. 2004; Liu et al. 2006b).”
• Hot Accretion Flows Around Black Holes (2014, methodology): “Observationally, non-thermal electrons are needed to explain the quiescent low-frequency radio emission in Sgr A* (Mahadevan 1998, Özel et al. 2000, Yuan et al. 2003; see §4.1) and other low-luminosity AGNs (Liu & Wu 2013), as well as the X-ray emission in flares in Sgr A* (Yuan et al. 2004).”
• PHOTON RINGS AROUND KERR AND KERR-LIKE BLACK HOLES (2013, methodology): “…et al. 2009), Broderick et al. (2009a, 2011a) combined the VLBI observations of Sgr A* with measurements of its spectral energy distribution (Yuan et al. 2004 and references therein; Marrone 2006) and obtained values of the spin magnitude and direction employing a radiatively inefficient…”
• EVIDENCE FOR LOW BLACK HOLE SPIN AND PHYSICALLY MOTIVATED ACCRETION MODELS FROM MILLIMETER-VLBI OBSERVATIONS OF SAGITTARIUS A* (2010, background): “All other points (red circles) are taken from Yuan et al. (2004) (and references therein) and were obtained by averaging over multiple epochs.”
• Polarimetry of near-infrared flares from Sagittarius A* (2006, methodology): “Stellar orbits near SgrA* make a universal Fermion ball solution for compact galactic nuclei highly unlikely (Schödel et al. 2002; Maoz 1998; see also Melia & Falcke 2001; Yuan et al. 2004).”
• The 511 keV emission from positron annihilation in the Galaxy (2010, methodology): “…considers pair production in the framework of the so-called Radiatively Inefficient Advection Flow (RIAF) model for accretion disks; this model, decoupling accretion from emerging luminosity, has been applied with considerable success to the case of Sgr A∗ (e.g. Yuan et al., 2004; Xu et al., 2006).”