Optical variability of radio-intermediate quasars

Goyal, A.; Gopal-Krishna, . .; Joshi, Santosh; Sagar, Ram; Wiita, Paul J.; Anupama, G. C.; Sahu, D. K.

doi:10.1111/j.1365-2966.2009.15846.x

Cited by 14 publications

(21 citation statements)

References 94 publications

(241 reference statements)

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“…Over the past two decades there have been rather extensive searches for this phenomenon in blazars, other types of radio‐loud quasi‐stellar objects (RLQSOs) and the far more numerous radio‐quiet quasars (RQQSOs) (e.g. Miller, Carini & Goodrich 1989; Carini et al 1992, Carini et al 2007; Gopal‐Krishna, Wiita & Altieri 1993b; de Diego et al 1998; Romero, Cellone & Combi 1999; Gopal‐Krishna et al 2000, 2003; Sagar et al 2004; Stalin et al 2004; Montagni et al 2006; Goyal et al 2010). In the case of blazars these studies have provided useful constraints on the relativistic jet based models that are used to explain the origin of the large variations that help define the category (e.g.…”

Section: Introductionmentioning

confidence: 99%

Optical microvariability properties of BALQSOs

Joshi

Chand

Gupta

et al. 2011

Monthly Notices of the Royal Astronomical Society

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We present optical light curves of 19 radio quiet (RQ) broad absorption line (BAL) QSOs and study their rapid variability characteristics. Systematic CCD observations, aided by a careful data analysis procedure, have allowed us to clearly detect any such microvariability exceeding 0.01--0.02 mag. Our observations cover a total of 13 nights (~72 hours) with each quasar monitored for about 4 hours on a given night. Our sample size is a factor of three larger than the number of radio-quiet BALQSOs previously searched for microvariability. We introduce a scaled F-test statistic for evaluating the presence of optical microvariability and demonstrate why it is generally preferable to the statistics usually employed for this purpose. Considering only unambiguous detections of microvariability we find that ~11 per cent of radio-quiet BALQSOs (two out of 19 sources) show microvariability for an individual observation length of about 4 hr. This new duty cycle of 11 per cent is similar to the usual low microvariability fraction of normal RQQSOs with observation lengths similar to those of ours. This result provides support for models where radio-quiet BALQSO do not appear to be a special case of the RQQSOs in terms of their microvariability properties.Comment: 13 pages, 3 figures, 3 tables, accepted for publication in MNRAS main journa

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Section: Introductionmentioning

confidence: 99%

Optical microvariability properties of BALQSOs

Joshi

Chand

Gupta

et al. 2011

Monthly Notices of the Royal Astronomical Society

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“…The occurrence of intranight optical variability (INOV), or microvariability, among quasars, particularly their more active subset called blazars, is now well documented in the literature (e.g., Miller et al 1989;Jang & Miller 1995Romero et al 1997Romero et al , 2002Gopal-Krishna et al 2003Sagar et al 2004;Stalin et al 2004aStalin et al ,b, 2005Gupta et al 2005Gupta et al , 2008Rani et al 2010;Goyal et al 2010). Considerable uncertainty persists, however, about the underlying physical mechanism and even from a purely observational perspective contrasting claims have been made (reviewed, e.g., by Wiita 2006;Wagner & Witzel 1995).…”

Section: Introductionmentioning

confidence: 99%

“…(c) In order to augment the sample, we included all 3 CDQs from the sample of Sagar et al (2004), for which Wills et al (1992) give P op < 2 per cent. These LPCDQs are J0958+3224, J1131+3114 and J1228+3128; J1312+3515 was not included as it is a radio-intermediate quasar (Goyal et al 2010). The intranight lightcurves for these 3 LPCDQs are taken from the study by Sagar et al (2004) which belongs to the first part of our INOV programme.…”

Section: The Lpcdq Samplementioning

confidence: 99%

“…Hitherto the criterion most commonly used in the literature for checking the presence of INOV is based on the so-called "C-statistic", which is defined as the ratio of standard deviations of the "QSO-star" DLC and the corresponding "star-star" DLC (e.g., Jang & Miller 1997;Romero et al 1999;Stalin et al 2004Stalin et al , 2005Xie et al 2004;Carini et al 2007;Gupta et al 2008;Goyal et al 2010). Recently, de Diego (2010 has emphasized that the usual definition of C is not a proper statistic, as it is based on the ratio of standard deviations which (unlike variance) are not lineal statistical operators.…”

Section: Inov Detection; F-statisticsmentioning

confidence: 99%

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Intra-night optical variability of core dominated radio quasars: the role of optical polarization

Goyal

Gopal-Krishna

Wiita

et al. 2012

A&A

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Context. Rapid variations in optical flux are seen in many quasars and all blazars. The amount of variability in different classes of active galactic nuclei has been studied extensively but many questions remain unanswered. Aims. We present the results of a long-term programme to investigate the intra-night optical variability (INOV) of powerful flat spectrum radio core-dominated quasars (CDQs), with a focus on probing the relationship of INOV to the degree of optical polarization. Methods. We observed a sample of 16 bright CDQs showing strong broad optical emission lines and consisting of both high and low optical polarization quasars (HPCDQs and LPCDQs). In this first systematic study of its kind, we employed the 104-cm Sampurnanand telescope, the 201-cm Himalayan Chandra telescope and the 200-cm IUCAA-Girawali Observatory telescope, to carry out R-band monitoring on a total of 47 nights. Using the CCD as an N-star photometer to densely monitor each quasar for a minimum duration of about 4 h per night, INOV exceeding ∼1-2 per cent could be reliably detected. Combining these INOV data with those taken from the literature, after ensuring conformity with the basic selection criteria we adopted for the 16 CDQs monitored by us, we were able to increase the sample size to 21 CDQs (12 LPCDQs and 9 HPCDQs) monitored on a total of 73 nights. Results. As the existence of a prominent flat-spectrum radio core signifies that strong relativistic beaming is present in all these CDQs, the definitions of the two sets differ primarily in fractional optical polarization, with the LPCDQs showing a very low median P op 0.4 per cent. Our study yields an INOV duty cycle (DC) of ∼28 per cent for the LPCDQs and ∼68 percent for HPCDQs. If only strong INOV with fractional amplitude above 3 per cent is considered, the corresponding DCs are ∼7 per cent and ∼40 per cent, respectively. Conclusions. From this strong contrast between the two classes of luminous, relativistically beamed quasars, it is apparent that relativistic beaming is normally not a sufficient condition for strong INOV and a high optical polarization is the other necessary condition. Moreover, the correlation is found to persist for many years after the polarization measurements were made. Some possible implications of this result are pointed out, particularly in the context of the recently detected rapid γ-ray variability of blazars.

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“…In fact, based on rapid radio flux variability, relativistically beamed jets are inferred to be common among RIQs (Wang et al 2006). However, a study of the optical variability of RIQs on hour to day-like time scales, based on intranight monitoring of 10 RIQs on 42 nights, has shown that while intra-night and inter-night optical variability is exhibited by RIQs, the INOV amplitude hardly ever exceeds 3 − 4%, in clear contrast to blazars (Goyal et al 2010). This is consistent with the inference that a relativistically beamed radio core of a quasar is not a sufficient condition for observing a pronounced INOV (Goyal et al 2012).…”

Section: Remarks On Possible Inov Eventsmentioning

confidence: 99%

Multi-epoch intra-night optical monitoring of 8 radio-quiet BL Lac candidates

Kumar

Gopal-Krishna

Stalin

et al. 2017

Monthly Notices of the Royal Astronomical Society

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For a new sample of 8 weak-line-quasars (WLQs) we report a sensitive search in 20 intranight monitoring sessions, for blazar-like optical flux variations on hour-like and longer time scale (day/month/year-like). The sample consists exclusively of the WLQs that are not radio-loud and have either been classified as 'radio-weak probable BL Lac candidates' and/or are known to have exhibited at least one episode of large, blazarlike optical variability. Whereas only a hint of intra-night variability is seen for two of these WLQs, J104833.5+620305.0(z = 0.219) and J133219.6+622715.9 (z = 3.15), statistically significant inter-night variability at a few per cent level is detected for three of the sources, including the radio-intermediate WLQ J133219.6+622715.9 (z = 3.15) and the well known bona-fide radio-quiet WLQs J121221.5+534128.0 (z = 3.10) and WLQ J153259.9−003944.1 (z = 4.62). In the rest-frame, this variability is intra-day and in the far-UV band. On the time scale of a decade, we find for three of the WLQs large brightness changes, amounting to 1.655±0.009, 0.163±0.010 and 0.144±0.018 mag, for J104833.5+620305.0, J123743.1+630144.9 and J232428.4+144324.4, respectively. Whereas the latter two are confirmed radio-quiet WLQs, the extragalactic nature of J104833.5+620305.0 remains to be well established, thanks to the absence of any feature(s) in its available optical spectra. The present study forms a part of our ongoing campaign of intranight optical monitoring of radio quiet weak-line quasars, in order to improve the understanding of this enigmatic class of Active Galactic Nuclei and to look among them for a possible tiny, elusive population of radio-quiet BL Lacs.

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Optical variability of radio-intermediate quasars

Cited by 14 publications

References 94 publications

Optical microvariability properties of BALQSOs

Optical microvariability properties of BALQSOs

Intra-night optical variability of core dominated radio quasars: the role of optical polarization

Multi-epoch intra-night optical monitoring of 8 radio-quiet BL Lac candidates

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