2 research outputs found
The June 2016 Optical and Gamma-Ray Outburst and Optical Micro-Variability of the Blazar 3C454.3
The quasar 3C454.3 underwent a uniquely-structured multi-frequency outburst
in June 2016. The blazar was observed in the optical band by several
ground-based telescopes in photometric and polarimetric modes, at -ray
frequencies by the \emph{Fermi}\ Large Area Telescope, and at 43 GHz with the
Very Long Baseline Array. The maximum flux density was observed on 2016 June 24
at both optical and -ray frequencies, reaching
mJy and ph cm s, respectively. The June 2016
outburst possessed a precipitous decay at both -ray and optical
frequencies, with the source decreasing in flux density by a factor of 4 over a
24-hour period in band. Intraday variability was observed throughout the
outburst, with flux density changes between 1 and 5 mJy over the course of a
night. The precipitous decay featured statistically significant quasi-periodic
micro-variability oscillations with an amplitude of - about the
mean trend and a characteristic period of 36 minutes. The optical degree of
polarization jumped from to nearly 20\% during the outburst, while
the position angle varied by \sim120\degr. A knot was ejected from the 43 GHz
core on 2016 Feb 25, moving at an apparent speed .
From the observed minimum timescale of variability
hr and derived Doppler factor
, we find a size of the emission region
cm. If the quasi-periodic micro-variability
oscillations are caused by periodic variations of the Doppler factor of
emission from a turbulent vortex, we derive a rotational speed of the vortex
.Comment: 19 pages, 13 figures, 3 tables, accepted to the Astrophysical Journal
2019 March
Multiband optical flux density and polarization microvariability study of optically bright blazars
We present the results of flux density, spectral index, and polarization
intra-night monitoring studies of a sample of eight optically bright blazars,
carried out by employing several small to moderate aperture (0.4\,m to 1.5\,m
diameter) telescopes fitted with CCDs and polarimeters located in Europe,
India, and Japan. The duty cycle of flux variability for the targets is found
to be percent, similar to that reported in earlier studies. The
computed two-point spectral indices are found to be between 0.65 to 1.87 for
our sample, comprised of low- and intermediate frequency peaked blazars, with
one exception; they are also found to be statistically variable for about half
the instances where `confirmed' variability is detected in flux density. In the
analysis of the spectral evolution of the targets on hourly timescale, a
counter-clockwise loop (soft-lagging) is noted in the flux-spectral index plane
on two occasions, and in one case a clear spectral flattening with the
decreasing flux is observed. In our data set, we also observe a variety of
flux-polarization degree variability patterns, including instances with a
relatively straightforward anti-correlation, correlation, or counter-clockwise
looping. These changes are typically reflected in the flux-polarization angle
plane: the anti-correlation between the flux and polarization degree is
accompanied by an anti-correlation between the polarization angle and flux,
while the counter-clockwise flux-PD looping behaviour is accompanied by a
clockwise looping in the flux-polarization angle representation. We discuss our
findings in the framework of the internal shock scenario for blazar sources.Comment: MNRAS accepte