Intra-night variability of the blazar CTA 102 during its 2012 and 2016 giant outbursts

Abstract

We obtained and analyzed more than 100 hours of multicolour optical time series of the blazar CTA 102 during its 2012 and 2016 outbursts. The object reached almost 11-th mag at the end of 2016, which is perhaps the brightest blazar state ever observed! During both outbursts, CTA 102 showed significant and rapid variability on intra-night time scales, reaching up to 0.2 mag for 30 min on some occasions. The "rms-flux" relation, built for all datasets, shows a large scatter and no apparent saturation on the magnitude scale. The ensemble structure function of the light curves can be fitted well with a straight line of a slope of ∼0.4. The time lags between the different optical bands appear to be consistent with zero, taking into account our time resolution. We discuss different variability scenarios and favor the changing Doppler factor of the emitting blobs as the most plausible one to account for the observed intra-night variability.

The Extended Flare in CTA 102 in 2016 and 2017 within a Hadronic Model through Cloud Ablation by the Relativistic Jet

“…These observations reveal a minimum variability time scale in the X-ray domain of 1.62 d, while the fastest variability revealed by UVOT observations is 0.88 d. The cadence of ATOM observations had also been increased a lot during the brightest state of the source. These reveal a very fast variability in the R-band of 0.03 d in line with Bachev et al (2017). B-band cadence was not as high as the R-band cadence and reveals a variability time scale of 0.48 d. As mentioned before, we focus on the long-term trend, and not on short time scales.…”

Fermi-Large Area Telescope Observations of the Brightest Gamma-Ray Flare Ever Detected from CTA 102

“…The late 2016 activity of CTA 102 was associated with intra-night variability in optical fluxes (Bachev et al 2017). During the late 2016 to early 2017 high state the brightest flare from this source has been observed.…”

Blazar variability -- expect the unexpected

“…Peak fluxes in the γ-ray domain rose by more than a factor 50 over the pre-flare level (even though that was already a factor of a few above the pre-2012 quiescent flux), while the optical flux rose by a factor 100 over the pre-flare level 4 [57]. Fast variability was observed in both bands [58,59]. A varying Doppler factor was again proposed as an explanation [60], which include different (i.e.…”