Rapid optical variability in radio-quiet QSOs

Gopal-Krishna, . .; Gupta, Alok C.; Sagar, Ram; Wiita, Paul J.; Chaubey, U. S.; Stalin, C. S.

doi:10.1046/j.1365-8711.2000.03446.x

Cited by 27 publications

(40 citation statements)

References 39 publications

(48 reference statements)

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“…It is statistically improbable that a significant number of random stars will turn out to be variable on time‐scales of an hour or so. Such comparison star variations are indeed reported in studies, where the quasar of interest is also sometimes found to vary similarly (Gopal‐Krishna et al 1995; Sagar et al 1996; Gopal‐Krishna et al 2000; GK03; S03). In any case, for those objects, for which evidence for short‐term variability is presented, an independent confirmation is by all means required.…”

Section: Discussionsupporting

confidence: 69%

Short-term optical variability of high-redshift quasi-stellar objects

Bachev

Strigachev

Semkov

2005

Monthly Notices of the Royal Astronomical Society

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In this paper we present the results of a search for short‐term variability in the optical band of selected high‐luminosity, high‐redshift radio‐quiet quasars. Each quasar has been monitored typically for 2–4 h with a time resolution of 2–5 min and a photometric accuracy of about 0.01–0.02 mag. As a result of the significant redshift (z > 2), the covered wavelength range falls into the ultraviolet region (typically 1500–2500 Å). We have found no statistical evidence for any continuum variations larger than 0.01–0.02 mag for any of the monitored objects. Our results suggest that the presence of a short‐term variability in radio‐quiet quasars is unlikely even in the ultraviolet region, contrary to reports by other authors. This conclusion holds true at least for high‐luminosity (large black hole mass and accretion rate?) objects. The results are consistent with the idea that significant short‐term (less than 1 h) variations in active galactic nuclei, where observed, should be attributed primarily to processes in a relativistic jet.

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Section: Discussionsupporting

confidence: 69%

Short-term optical variability of high-redshift quasi-stellar objects

Bachev

Strigachev

Semkov

2005

Monthly Notices of the Royal Astronomical Society

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“…This work provided the first positive detection of INOV for RQQs, though modest evidence for such variations had been obtained earlier (e.g. Gopal‐Krishna, Sagar & Wiita 1995; Sagar, Gopal‐Krishna & Wiita 1996; Jang & Miller 1997; Gopal‐Krishna et al 2000). It was, moreover, found that except for BLs and high optical polarization CDQs (HP‐CDQs), the amplitude of detected INOV is small (≤3 per cent) and so is the INOV duty cycle (DC; ∼10–20 per cent), irrespective of the radio loudness.…”

Section: Introductionsupporting

confidence: 51%

Intranight optical variability of BL Lacs, radio-quiet quasars and radio-loud quasars

Stalin¹,

Gupta²,

Gopal-Krishna³

et al. 2005

Monthly Notices of the Royal Astronomical Society

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102

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We report monitoring observations of 20 high‐luminosity active galactic nuclei (AGN), 12 of which are radio‐quiet quasars (RQQs). Intranight optical variability (INOV) was detected for 13 of the 20 objects, including 5 RQQs. The variations are distinctly stronger and more frequent for blazars than for the other AGN classes. By combining these data with results obtained earlier in our programme, we have formed an enlarged sample consisting of 9 BL Lacs, 19 RQQs and 11 lobe‐dominated radio‐loud quasars (RLQs). The moderate level of rapid optical variability found for both RQQs and radio lobe‐dominated quasars (LDQs) argues against a direct link between INOV and radio loudness. We supplemented the present observations of 3 BL Lacs with additional data from the literature. In this extended sample of 12 well observed BL Lacs, stronger INOV is found for the EGRET detected subset.

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“…Unfortunately, such micro-arcsec scales are beyond the reach of any existing imaging telescopes and the only way to probe the conditions at such small scales is through flux variability observations. Though intra-night optical variability (INOV) was convincingly established for blazars over a decade ago (Miller, Carini & Goodrich 1989), the question of whether RQQs too show INOV has remained controversial (Gopal- Krishna et al 1995Krishna et al , 2000Jang & Miller 1995Rabbette et al 1998, de Diego et al 1998; Romero et al 1999). The cause of INOV is still a much debated issue.…”

Section: Introductionmentioning

confidence: 99%

Optical variability properties of high luminosity AGN classes

et al. 2004

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1We present the results of a comparative study of the intra-night optical variability (INOV) characteristics of radio-loud and radio-quiet quasars, which involves a systematic intra-night optical monitoring of seven sets of high luminosity AGNs covering the redshift range z 0.2 to z 2.2. The sample, matched in the optical luminosity -redshift (M B -z) plane, consists of seven radio-quiet quasars (RQQs), eight radio lobe-dominated quasars (LDQs), six radio core-dominated quasars (CDQs) and five BL Lac objects (BLs). Systematic CCD observations, aided by a careful data analysis procedure, have allowed us to detect INOV with amplitudes as low as 1%. Present observations cover a total of 113 nights (720 hours) with only a single quasar monitored as continuously as possible on a night. Considering cases of only unambiguous detections of INOV we have estimated duty cycles (DCs) of 17%, 12%, 20% and 72% respectively for RQQs, LDQs, CDQs, and BLs. The low amplitude and low DC of INOV shown by RQQs compared to BLs can be understood in terms of their having optical synchrotron jets which are modestly misdirected from us. From our fairly extensive dataset, no unambiguous general trend of a correlation between the INOV amplitude and the apparent optical brightness of the quasar is noticed. This suggests that the physical mechanisms of INOV and long term optical variability (LTOV) do not have a one-to-one relationship and different factors are involved. Also, the absence of a clear negative correlation between the INOV and LTOV characteristics of blazars of our sample points towards an inconspicuous contribution of accretion disk flucutations to the observed INOV. The INOV duty cycle of the AGNs observed in this program suggests that INOV is associated predominantly with highly polarised optical components. We also report new VLA imaging of two RQQs (1029+329 & 1252+020) in our sample which has yielded a 5 GHz detection of one of them (1252+020; S = 1 mJy).

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Rapid optical variability in radio-quiet QSOs

Cited by 27 publications

References 39 publications

Short-term optical variability of high-redshift quasi-stellar objects

Short-term optical variability of high-redshift quasi-stellar objects

Intranight optical variability of BL Lacs, radio-quiet quasars and radio-loud quasars

Optical variability properties of high luminosity AGN classes

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