Multifrequency Photo-Polarimetric Webt Observation Campaign on the Blazar S5 0716+714: Source Microvariability and Search for Characteristic Timescales*

Abstract

Here we report on the results of the WEBT photo-polarimetric campaign targeting the blazar S5 0716+71, organized in March 2014 to monitor the source simultaneously in BVRI and near IR filters. The campaign resulted in an unprecedented dataset spanning ∼ 110 h of nearly continuous, multi-band observations, including two sets of densely sampled polarimetric data mainly in R filter. During the campaign, the source displayed pronounced variability with peak-to-peak variations of about 30% and "bluer-when-brighter" spectral evolution, consisting of a day-timescale modulation with superimposed hourlong microflares characterized by ∼ 0.1 mag flux changes. We performed an in-depth search for quasi-periodicities in the source light curve; hints for the presence of oscillations on timescales of ∼ 3 h and ∼ 5 h do not represent highly significant departures from a pure rednoise power spectrum. We observed that, at a certain configuration of the optical polarization angle relative to the positional angle of the innermost radio jet in the source, changes in the polarization degree led the total flux variability by about 2 h; meanwhile, when the relative configuration of the polarization and jet angles altered, no such lag could be noted. The microflaring events, when analyzed as separate pulse emission components, were found to be characterized by a very high polarization degree (> 30%) and polarization angles which differed substantially from the polarization angle of the underlying background component, or from the radio jet positional angle. We discuss the results in the general context of blazar emission and energy dissipation models.

Optical monitoring of BL Lac object S5 0716+714 and FSRQ 3C 273 from 2000 to 2014

“…Intra-day variabilities (IDVs) have been studied by many authors (Poon et al 2009;Liu et al 2012;Gupta et al 2012;Bhatta et al 2013;Man et al 2016;Lee et al 2016, etc.). Gupta et al (2009) obtained timescales of 25 min; Rani et al (2010) obtained timescales of 15 min; Man et al (2016) obtained timescales of 17.6 min; and Bhatta et al (2016) displayed the variability based on the A&A 605, A43 (2017) peak-to-peak variations of 30% and "bluer-when-brighter" spectral evolution.…”

Investigating the Innermost Jet Structures of Blazar S5 0716+714 Using Uniquely Dense Intra-day Photo-polarimetric Observations

“…In such a scenario, the electrons with lower energies E e ∝ 1/ √ B in an amplified magnetic field intensity B would produce enhanced synchrotron emission at a given observed frequency, representing, in the present context, microflares with bluer color (flatter spectra). On the other hand, the 6 h plateau seen both in the 2014 and the 2003 campaigns can be used to place a constraint on the upper limit for the S5 0716+714 black hole mass, which can be estimated as M 4 × 10 9 M for a maximally spinning supermassive black hole (SMBH) (r isco r g ), and M 3 × 10 8 M for very low spin values (r isco 6 r g ) (For details on the calculations, see [18]). The study of the polarization properties revealed that any coherent correlation between flux and polarization properties (e.g., PD leading the total flux changes, hysteresis in the PD-F plane) might depend on the particular configuration of the orientation of ambient magnetic field in relation to the direction of the radio core of the jet.…”

“…The data gathered during the period are shown in Figure 2; the vertical lines on Figure 2 mark the microflares we considered for the detailed analysis. The list of the participating observatories and other details on the observational campaign are described in [18]. As explained earlier, one of the primary motivations of these extended campaigns was to probe the temporal behavior of the source in the rather-unexplored time domain spanning from more than 12 h up to few days, without major interruption in between.…”

“…S5 0716+714 has also been detected by γ-ray instruments such as the Compton EGRET, AGILE, Fermi-LAT satellites and also by the MAGIC Cherenkov telescope (see, e.g., [11][12][13][14] and references therein). In particular, there have been numerous optical microvariability studies of S5 0716+714 which reported many interesting results, including achromatic behavior, red noise-type power spectra, and in some cases, correlation between flux and polarization degree [15][16][17][18]. In this proceeding, we present the summary of our optical microvariability studies on S5 0716+714, over the past few years, based on multifrequency photo-polarimetric Whole Earth Blazar Telescope (WEBT) [18,19] observation campaigns in 2009 and 2014 (the data collected by the WEBT Collaboration are stored in the WEBT archive; for questions regarding their availability, please contact the WEBT President Massimo Villata: villata@oato.inaf.it).…”

Automated Polarimetry with Smaller Aperture Telescopes: The ROVOR Observatory

“…Setup takes place during the day, the telescope performs all observations at night without operator assistance, and shuts down automatically at dawn. Over 30 students have been trained on it, while producing or contributing to approximately one refereed monitoring paper per year (e.g., [4][5][6][7][8][9][10]). …”