A Black Hole Mass-Variability Time Scale Correlation at Submillimeter Wavelengths

TL;DR

This study finds a linear correlation between variability time scales and black hole mass in low luminosity active galactic nuclei at submillimeter wavelengths, indicating a potential universal physics near event horizons.

Contribution

It introduces a method to measure variability time scales at submm wavelengths and establishes a correlation with black hole mass for LLAGN, including new measurements for M81 and M87.

Findings

Measured variability time scales for M81 and M87.

Established a linear correlation between time scale and black hole mass.

Suggests similar physics near event horizons across different black hole systems.

Abstract

We analyze the light curves of 413 radio sources at submillimeter wavelengths using data from the Submillimeter Array calibrator database. The database includes more than 20,000 observations at 1.3 and 0.8 mm that span 13 years. We model the light curves as a damped random walk and determine a characteristic time scale $\tau$ at which the variability amplitude saturates. For the vast majority of sources, primarily blazars and BL Lac objects, we find only lower limits on $\tau$. For two nearby low luminosity active galactic nuclei, M81 and M87, however, we measure $\tau=1.6^{+3.0}_{-0.9}$ days and $\tau=45^{+61}_{-24}$ days, respectively ($2\sigma$ errors). Including the previously measured $\tau=0.33\pm 0.16$ days for Sgr A*, we show an approximately linear correlation between $\tau$ and black hole mass for these nearby LLAGN. Other LLAGN with spectra that peak in the submm are expected to follow this correlation. These characteristic time scales are comparable to the minimum time scale for emission processes close to an event horizon, and suggest that the underlying physics may be independent of black hole mass, accretion rate, and jet luminosity.