Fast Variability and mm/IR flares in GRMHD Models of Sgr A* from Strong-Field Gravitational Lensing

Abstract

We explore the variability properties of long, high cadence GRMHD simulations across the electromagnetic spectrum using an efficient, GPU-based radiative transfer algorithm. We focus on both disk- and jet-dominated simulations with parameters that successfully reproduce the time-averaged spectral properties of Sgr A* and the size of its image at 1.3mm. We find that the disk-dominated models produce short timescale variability with amplitudes and power spectra that closely resemble those inferred observationally. In contrast, jet-dominated models generate only slow variability, at lower flux levels. Neither set of models show any X-ray flares, which most likely indicate that additional physics, such as particle acceleration mechanisms, need to be incorporated into the GRMHD simulations to account for them. The disk-dominated models show strong, short-lived mm/IR flares, with short (<~ 1hr) time lags between the mm and IR wavelengths, that arise from strong-field gravitational lensing of magnetic flux tubes near the horizon. Such events provide a natural explanation for the observed IR flares with no X-ray counterparts.

14 pages, 12 figures, submitted to ApJ

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• Evolving Nonthermal Electrons in Simulations of Black Hole Accretion
• The Properties of Reconnection Current Sheets in GRMHD Simulations of Radiatively Inefficient Accretion Flows
• The Effects of Accretion Flow Dynamics on the Black Hole Shadow of Sagittarius A${}^{\ast }$
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• Simultaneous X-ray and Infrared Observations of Sagittarius A*'s Variability
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• Multiwavelength Light Curves of Two Remarkable Sagittarius A* Flares
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