Multiband optical flux density and polarization microvariability study of optically bright blazars

Abstract

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 ∼ 45 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 counterclockwise 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 counterclockwise 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.

Radiation and Polarization Signatures from Magnetic Reconnection in Relativistic Jets--I. A Systematic Study

“…Therefore, the radiation and polarization signatures that we present in this paper can happen on very short time scales. Interestingly, such micro-variability patterns have been reported in observations (e.g., Pasierb et al 2019). On the other hand, in a striped jet morphology, the magnetic stripes are created at the central engine and propagate out along with the jet.…”

“…Therefore, we do not expect any large ( 90 • ) PA rotations from reconnection in kink instabilities or magnetic turbulence. Very interestingly, the blazar micro-variability, which may originate from reconnection in magnetic instabilities/turbulence, mostly shows small PA fluctuations (Pasierb et al 2019). In contrast, in the striped jet scenario, a large region of anti-parallel magnetic field lines with small guide fields is probable.…”

Multi-band behaviour of the TeV blazar PG 1553+113 in optical range on diverse timescales

“…Employing enhanced F-and nested ANOVA tests, the authors found the source to vary on intra-night timescales for three nights. Finally, Pasierb et al (2020) found no INV in the BVR-bands during a single night of monitoring (duration of about 3.7 hr, F-test employed).…”

Optical variability power spectrum analysis of blazar sources on intranight timescales

“…Annihilation of magnetic field lines at the reconnection sites within the jet plasma can also impart energy to the particles (Giannios 2013;Sironi et al 2015); this scenario is supported by the recent detection of minutelike variability at GeV energies for the blazar 3C 279 (Shukla & Mannheim 2020). On the other hand, flux changes on the intranight timescales have also been associated with variable Doppler boosting factors related to changes in the viewing angle of the emitting plasma (e.g., Gopal-Krishna & Wiita 1992), although in such a scenario frequency-independent variability is expected (see, in this context, Pasierb et al 2020).…”