Magnetic Field Strengths of the Synchrotron Self-Absorption Region in
  the Jet of CTA 102 During Radio Flares
  CTA 102 is a blazar implying that its relativistic jet points towards Earth
and emits synchrotron radiation produced by energetic particles gyrating in the
magnetic field. This study aims to figure out the physical origins of radio
flares in the jet, including the connection between the magnetic field and the
radio flares. The dataset in the range 2.6-343.5 GHz was collected over a
period of 5.5 years (2012 November 20-2018 September 23). During the data
collection period, seven flares at 15 GHz with a range of the variability
time-scale of roughly 26-171 days were detected. The quasi-simultaneous radio
data were used to investigate the synchrotron spectrum of the source. We found
that the synchrotron radiation is self-absorbed. The turnover frequency and the
peak flux density of the synchrotron self-absorption (SSA) spectra are in the
ranges of 42-167 GHz and 0.9-10.2 Jy, respectively. From the SSA spectra, we
derived the SSA magnetic field strengths to be 9.20 mG, 12.28 mG, and 50.97 mG
on 2013 December 24, 2014 February 28, and 2018 January 13, respectively. We
also derived the equipartition magnetic field strengths to be in the range
24-109 mG. The equipartition magnetic field strengths are larger than the SSA
magnetic field strengths in most cases, which indicates that particle energy
mainly dominates in the jet. Our results suggest that the flares in the jet of
CTA 102 originated due to particle acceleration. We propose the possible
mechanisms of particle acceleration.
