Intranight optical variability of radio-quiet weak emission line quasars – II

Abstract

Rapid intranight variability of continuum and polarization in blazars is a very useful tool to probe the beaming of a relativistic jet and the associated population of the relativistic particles. Such intranight variability in the rest-frame optical continuum has been carried out extensively, but there is a scarcity of such information in the rest-frame ultra-violet (UV), where the cause of variability might be due to a secondary population of relativistic particles. To fill this gap, recently in Chand et al. ( 2022) we reported for the first time intranight variability study of a sample of high-z blazars so that the monitored optical radiation is their rest-frame UV radiation.Here we discuss in detail the implication of this investigation with a proper comparison of highz blazar samples with fractional optical polarization (p opt ) smaller and higher than 3%. In this context, we also report intranight variability study of an additional high-z blazar at z=2.347, namely J161942.38+525613.41, monitored over three sessions each with a duration of ∼5 hr. Our investigation does not reveal any compelling evidence for a stronger intranight variability of UV emission for high polarization blazars, in contrast to the blazars monitored in the rest-frame blue-optical. We also discuss this trend in light of the proposal that the synchrotron radiation of blazar jets in the UV/X-ray regime may arise from a relativistic particle population different from that radiating up to near-infrared/optical frequencies.

On the Reliability of Microvariability Tests in Quasars

“…The way that multitesting is implemented is that for being considered a trusty detection, a microvariation should be discerned by two tests at a significance level α = 0.01 (e.g. Joshi et al 2011;Hu et al 2013;Chand et al 2014).…”

“…As a mutitesting procedure, DPT outcomes cannot be accurately described in terms of probabilities, and by construction, these outcomes are biased by the test that has the lower power. DPT is the actual methodology employed in some recent microvariability research (e.g., Joshi et al 2011;Gaur et al 2012;Hu et al 2013;Chand et al 2014). For example, Hu et al (2013) test variability in the BL Lac object OI 090.4 using the C-test and the F -test, and they claim variability only if both tests reject the null hypothesis at the significance level of α = 0.01, or a dubious event if only one of the tests reveals variability.…”

Intranight optical variability of radio-quiet weak emission line quasars – III

“…Optical flux variation on hourlike time scale, which is commonly known as 'intranight optical variability' (INOV), has emerged as a useful probe of AGN (Wagner & Witzel 1995;Ulrich et al 1997;Wiita 2006). The past two decades have witnessed a large number of INOV studies covering different classes of AGN, in order to study the physical processes underlying this phenomenon occurring in the different AGN classes (Miller et al 1989;Heidt & Wagner 1996;Carini et al 1990Carini et al , 1991Carini et al , 2007Gopal-Krishna et al 1995Stalin et al 2004b ⋆ E-mail: parveen@aries.res.in (PK); gopaltani@gmail.com (GK); hum@aries.res.in (HC) Goyal et al 2013;Chand et al 2014;de Diego 2014). These studies have led to theoretical models for INOV (e.g, see Ulrich et al 1997;Czerny et al 2008;Wiita 2006).…”

“…They exhibit abnormally weak broad emissionlines (i.e, rest-frame EW< 15.4Å for the Ly+NV emissionline complex, Diamond-Stanic et al 2009). The physical cause for the abnormally weak line emission continues to be debated, as summarized in the previous papers of this series Chand et al 2014, hereinafter Paper I & Paper II). It may be recalled that according to the currently prevailing view, the two sub-classes of the most active AGN, called blazars, are BL Lac objects (BLOs) and Highly-Polarized-Quasars (HPQs) which differ primarily in the prominence of emission lines in the optical spectrum.…”

Intranight optical variability of radio-quiet BL Lacertae objects

“…However, it is still unclear whether the intranight variation is frequent in the radio-quiet BL Lac objets, which will be helpful in distinguishing the origin of their continua. Gopal-Krishna et al (2013 and Chand et al (2014 claim that they have detected a considerable fraction of intranight variation in a sample of weak-line AGNs (duty cycle ∼5%), and this fraction can be higher if the signalto-noise ratio of the light curve is further increased. However, as we discuss in this paper, some galactic sources may contaminate their sample.…”