Polarimetric and spectroscopic study of radio-quiet weak emission line quasars

Abstract

A small subset of optically selected radio-quiet quasars showing weak or no emission lines may turn out to be the elusive radio-quiet BL Lac objects, or simply be radioquiet QSOs with a still-forming/shielded broad line region (BLR). High polarisation (p > 3−4%), a hallmark of BL Lacs, can be used to test whether some optically selected 'radio-quiet weak emission line quasars' (RQWLQs) show a fractional polarisation high enough to qualify as radio-quiet analogs of BL Lac objects. Out of the observed six RQWLQs candidates showing an insignificant proper motion, only two are found to have p > 1%. For these two RQWLQs, namely J142505.59+035336.2, J154515.77+003235.2, we found polarisation of 1.03±0.36%, 1.59±0.53% respectively, which again is too modest to justify a (radio-quiet) BL Lac classification. We also present here a statistical comparison of the optical spectral index, for a set of 40 RQWLQs with redshift-luminosity matched control sample of 800 QSOs and an equivalent sample of 120 blazars. The spectral index distribution of RQWLQs is found to differ, at a high significance level, from that of blazars and is consistent with that of the ordinary QSOs. Likewise, a structure-function analysis of photometric light curves presented here suggests that the mechanism driving optical variability in RQWLQs is similar to that operating in QSOs and different from that of blazars. These findings are consistent with the common view that the central engine in RQWLQs, as a population, is akin to that operating in normal QSOs and the primary differences between them might be related to differences in the BLR.

Intra-night optical monitoring of three γ-ray detected narrow-line Seyfert 1 galaxies

“…⋆ E-mail: vineet@aries.res.in Gupta & Joshi 2005;Carini et al 2007;Ramírez et al 2009;Goyal et al 2012Goyal et al , 2013aKumar et al 2017).…”

Improved Constraints on Anisotropic Birefringent Lorentz Invariance and CPT Violation from Broadband Optical Polarimetry of High Redshift Galaxies

“…6. Kumar+2018 [77] Test for misclassification of BL Lac sources as radioquiet quasars through optical polarimetry. All observations were obtained with EFOSC2 (ESO's New Technology Telescope).…”

Intra-night optical variability of $γ-$ray detected narrow-line Seyfert 1 galaxies

“…As recently summarised in Gopal-Krishna & Wiita (2018), prominent among the radio-quiet AGNs covered extensively in INOV studies are radioquiet Seyfert galaxies (Carini et al 2003), radio-quiet quasars (Gopal-Krishna et al 2003), and weak emission line quasars (Gopal-Krishna et al 2013;Chand et al 2014;Kumar et al 2015Kumar et al , 2016Kumar et al , 2017. A possible cause for the low-level INOV detections in some such cases is the transient formation of micro-arcsec scale, probably in poorly aligned optical synchrotron jets (see, Gopal-Krishna et al 2003;Stalin et al 2004).…”

“…AGN variability on minutes to hour-like time scales in the optical waveband is termed as intra-night optical variability (INOV, Gopal-Krishna et al 1993). Such variations have proved particularly useful for probing and characterising the jet activity in blazars and radioloud narrow-line Seyfert 1 (NLSy1) galaxies, as well as ⋆ E-mail: vineet@aries.res.in, vineetojhabhu@gmail.com for identifying any blazar-like signatures in radio-quiet AGNs (e.g., Miller et al 1989;Gopal-Krishna et al 1993Jang & Miller 1995;Heidt & Wagner 1996;Bai et al 1999;Romero et al 1999;Fan et al 2001;Stalin et al 2004;Gupta & Joshi 2005;Carini et al 2007;Ramírez et al 2009;Goyal et al 2012Goyal et al , 2013Kumar et al 2017;Paliya 2019;Ojha et al 2019). In the case of blazars, INOV is generally associated with disturbances within their relativistic jets, e.g., the well-known "shock-in-jet" model (e.g., see Marscher & Gear 1985;Hughes et al 1991;Qian et al 1991;Wagner & Witzel 1995;Marscher 1996).…”