Possible Gravitational Microlensing Events in the Optical Lightcurve of Active Galaxy S5 0716+714

TL;DR

This paper suggests that symmetric, volcano-like optical lightcurve events in the blazar S5 0716+714 may be caused by gravitational microlensing from a binary black hole system within the galaxy, revealing potential evidence of intermediate-mass and dual supermassive black holes.

Contribution

The study introduces a novel interpretation of blazar variability as gravitational microlensing by a binary black hole, supported by detailed modeling and fitting of observed events.

Findings

Successful fit of all selected events with a single lens model

Postulation of a binary lens system with an intermediate-mass black hole

Implications for the existence of dual supermassive black holes in active galaxies

Abstract

A well-known active galaxy of the blazar type, S5 0716+714, is characterized by a particularly high variability duty cycle on short-time scales at optical frequencies. As such, the source was subjected to numerous monitoring programs, including both ground-based as well as space-borne telescopes. On closer inspection of the most recent accumulation of the data provided by the Transiting Exoplanet Survey Satellite, we have noticed several conspicuous events with `volcano-like' symmetric shape, lasting all for several hours, which closely resemble the achromatic events detected with the previous Whole Earth Blazar Telescope campaigns targeting the source. We propose that those peculiar features could be due to the gravitational micro-lensing of the innermost segments of the precessing jet in the system, by a binary lens. We study the magnification pattern of the lens with the inverse-ray shooting method, and the source trajectory parameters with the Python package MuLensModel. In this way, we were able to fit successfully all the selected events with a single lens, adjusting slightly only the source trajectory parameters for each lensing event. Based on the fit results, we postulate the presence of a massive binary lens, containing an intermediate-mass black hole, possibly even a super-massive one, and a much less massive companion (by a factor of $\lesssim 0.01$), located within the host galaxy of the blazar, most likely the central kiloparsec region. We discuss the major physical implications of the proposed scenario regarding the quest for the intermediate-mass and dual supermassive black holes in active galaxies.