Long-term multi-band photometric monitoring of Mrk 501

TL;DR

This study presents a comprehensive multi-year, multi-band observational analysis of Mrk 501, revealing correlated X-ray and TeV variability consistent with SSC emission and suggesting jet precession as a flare driver.

Contribution

It provides the first detailed long-term multi-wavelength correlation analysis of Mrk 501, linking variability patterns to emission mechanisms and jet dynamics.

Findings

Detected sub-day lag between X-ray and TeV emissions.

Confirmed SSC as the primary emission process during flares.

Identified 5-25 day intervals between TeV flares linked to jet precession.

Abstract

Radio-to-TeV observations of the bright nearby (z=0.034) blazar Markarian 501 (Mrk 501), performed from December 2012 to April 2018, are used to study the emission mechanisms in its relativistic jet. We examined the multi-wavelength variability and the correlations of the light curves obtained by eight different instruments, including the First G-APD Cherenkov Telescope (FACT), observing Mrk 501 in very high-energy (VHE) gamma-rays at TeV energies. We identified individual TeV and X-ray flares and found a sub-day lag between variability in these two bands. Simultaneous TeV and X-ray variations with almost zero lag are consistent with synchrotron self-Compton (SSC) emission, where TeV photons are produced through inverse Compton scattering. The characteristic time interval of 5-25 days between TeV flares is consistent with them being driven by Lense-Thirring precession.