Long-Term Radio Modulation in Sagittarius A* from Spin-Induced Disk Precession

Abstract

There is some evidence, though yet unconfirmed, that Sagittarius A*--the supermassive black hole at the Galactic center--emits its radio waves modulated with a ~100-day period. What is intriguing about this apparent quasi-periodicity is that, though the amplitude of the modulation increases with decreasing wavelength (from 3.6 to 1.3 cm), the quasi-period itself does not seem to depend on the frequency of the radiation. It is difficult to imagine how a binary companion, were that the cause of this modulation, could have escaped detection until now. Instead, it has been suggested that the spin-induced precession of a disk surrounding a slowly rotating black hole could have the right period to account for this behavior. In this paper, we examine how Sagittarius A*'s light curve could be modulated by this mechanism. We demonstrate that the partial occultation of a nonthermal halo by a compact, radio-opaque disk does indeed produce the observed frequency-dependent amplitude. This appears to be in line with other observational arguments suggesting that Sagittarius A*'s mm/sub-mm spectrum is produced by a ~10 Schwarzschild-radius disk, whereas its cm-waves originate from a nonthermal particle distribution in a halo extending out to over 20 Schwarzschild radii. Interestingly, this model suggests that the observed period corresponds to half the precession period and that a non-axisymmetric disk could produce a second period roughly twice as long as the first.

17 pages, 5 figures, accepted to ApJ

References in corpus (14)

• Near-infrared flares from accreting gas around the supermassive black hole at the Galactic Centre
• Rapid X-ray flaring from the direction of the supermassive black hole at the Galactic Centre
• The Supermassive Black Hole at the Galactic Center
• Detection of the Intrinsic Size of Sagittarius A* through Closure Amplitude Imaging (includes Online Supporting Material)
• Hydrodynamic Simulations of the Bardeen-Petterson Effect
• Hydrodynamical Accretion Onto Sgr A* From Distributed Point Sources
• Polarimetric Imaging of the Massive Black Hole at the Galactic Center
• Radio Variability of Sagittarius A* - A 106 Day Cycle
• The Linear Polarization of Sagittarius A* I. VLA Spectro-polarimetry at 4.8 and 8.4 GHz
• Spin-Induced Disk Precession in the Supermassive Black Hole at the Galactic Center
• New Constraints on the Nature of Radio Emission in Sagittarius A*
• 7 mm lambda VLBA Observations of Sagittarius A*
• BIMA Observations of Linear Polarization in Sagittarius A* at 112 GHz
• Measuring the Black Hole Spin in Sgr A*

Cited by in corpus (6)

• The pattern of accretion flow onto Sgr A*
• Motion of Spinning Particles around Electrically Charged Black Hole in Eddington-inspired Born-Infeld Gravity
• Spin-Induced Disk Precession in Sagittarius A*
• Motion of test particle in rotating boson star
• Low angular momentum flow model of Sgr A* activity
• SgrA* emission at 7mm: variability and periodicity