Long-term multi-band photometric monitoring of Mrk 501
  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.
