Speaker
Description
Blazars are known to show variability on time scales from minutes to
years. This complicates the measurement of their ground state. For
this, long-term monitoring is important to increase the chance to study
the source in an all-time low state.
The First G-APD Cherenkov Telescope (FACT) is monitoring bright TeV
blazars since more than six years and has collected between 1500 and
3000 hours of physics data per source for Mrk 421, Mrk 501, 1ES
1959+650 and 1ES 2344+51.4.
Studying flux distributions of the FACT light curves, both on the
complete sample and on shorter time scales, the ground state of the
sources is confined and the evolution of the flux level with time is
measured.
The results of the study are used to determine trigger levels for
automatic alerts to the AMON network for the generation of real-time
multi-messenger coincidence alerts.
While Mrk 421 was active in all observing seasons, Mrk 501 and 1ES
1959+650 had both very active and very quiet seasons. 1ES 1959+650
showed a bright flaring activity in 2016 and slightly enhanced flux in
2015, 2017 and 2018. Mrk 501 was very active from 2012 till 2014. Then
its flux decreased reaching a low level in 2017 and 2018.
In the presentation, the evolution of the flux levels and upper limits
on all-time low states of the sources will be discussed.
