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

Abstract

We report an extension of our program to search for radio-quiet BL Lac candidates using intra-night optical variability (INOV) as a probe. The present INOV observations cover a well-defined representative set of 10 'radio-quiet weak-emission-line quasars' (RQWLQs), selected from a newly published sample of 46 such sources, derived from the Sloan Digital Sky Survey (Data release 7). Intra-night CCD monitoring of the 10 RQWLQs was carried out in 18 sessions lasting at least 3.5 hours. For each session, differential light curves (DLCs) of the target RQWLQ were derived relative to two steady comparison stars monitored simultaneously. Combining these new data with those already published by us for 15 RQWLQs monitored in 30 sessions, we estimate an INOV duty cycle of ∼ 3% for the RQWLQs, which appears inconsistent with BL Lacs. However, the observed INOV events (which occurred in just two of the sessions) are strong (with a fractional variability amplitude ψ > 10%), hence blazar-like. We briefly point out the prospects of an appreciable rise in the estimated INOV duty cycle for RQWLQs with a relatively modest increase in sensitivity for monitoring these rather faint objects.

Intra-night optical variability of AGN in the COSMOS field with the KMTNet

“…This is roughly consistent with the 2% in our results, considering that most of AGNs in this study have higher photometric uncertainty than 095834.0+024427. In addition, Webb & Malkan (2000), Carini et al (2003), Klimek et al (2004), Bachev et al (2005), and Kumar et al (2016), show no variability or very small fraction of variability with ∼ 10 −2 mag photometric error. However, when investigating INOV of a very small amplitude (0.01 or less), we caution that there can be intrinsic errors such as the one we discussed in Section 5.…”

“…When smaller amplitudes of INOV are examined, the results are rather mixed. Examining the INOV amplitude down to about 1%, several studies find 10-40% of radio-quiet quasars show INOV with the duty cycle of 10-20% (Jang & Miller 1995Romero et al 1999Romero et al , 2002Gopal-Krishna 2000Webb & Malkan 2000;Stalin et al 2004aStalin et al ,b, 2005Klimek et al 2004;Bachev et al 2005;Gupta & Joshi 2005;Carini et al 2007;Goyal et al 2010Goyal et al , 2012Goyal et al , 2013aJoshi et al 2011;Kumar et al 2016), while several other studies that examined INOV at a similar level do not find such evidence (Petrucci et al 1999;Romero et al 1999). For example, Goyal et al (2013a) find that about 40% of radio-quiet quasars exhibit INOV, and 20% if limited to the variability amplitude of ∼ 3%.…”

“…On the other hand, radio-quiet AGNs show INOV much less frequently, but the results are more controversial than the case for radio-loud AGNs. In general, it is accepted that the INOV is found in none or only a few % of radio-quiet AGNs of various kinds when the variability amplitude of a few percent is examined (Romero et al 1999;Webb & Malkan 2000;Klimek et al 2004;Bachev et al 2005;Carini et al 2007;Kumar et al 2016), where the variability amplitude is defined as the ratio of the standard deviation of the AGN light curve versus the observational error being > 2.576 or so (99% confidence; Jang & Miller 1997). Webb & Malkan (2000) examined INOV of 20 Seyfert 1 AGNs, and found no INOV with the upper limit on the amplitude of the variation of 0.03 mag for time scales of 1 hr or less.…”

“…Using photometric data at an accuracy of 0.02 mag, Carini et al (2007) find no INOV among 7 quasars (5 radio-quiet and 2 radio-intermediate). Kumar et al (2016) examined the INOV of 10 weak emission line quasars (WLQ) in the hope of identifying BL Lacs with a peculiar property, but they found no INOV among 18 observing sessions. Their work has photometric error of 0.03 to 0.06 mag, so INOV of 0.1 mag or larger should have been detected.…”

Intra-night optical variability study of a non-jetted narrow-line Seyfert 1 galaxy: SDSS J163401.94+480940.1

“…QSOs. In fact, this tool has been used for a decade as a diagnostic to search for the Doppler boosted optical jets in X-ray detected NLSy1s, γ-ray detected NLSy1s, and weak emission line QSOs (e.g., see Liu et al, 2010;Paliya et al, 2013a;Kumar & Gopal-Krishnaand Chand, 2015;Kumar et al, 2016Kumar et al, , 2017Ojha et al, 2018Ojha et al, , 2019Ojha et al, , 2021. Therefore, to continue these variability studies, we present here the intra-night variability study of a RLNLSy1 galaxy (R = 204) SDSS J163401.94+480940.2, which we observed with 3.6m Devasthal Optical Telescope (DOT) of the Aryabhatta Research Institute of observational SciencES (ARIES), India.…”