Optical variability of radio-intermediate quasars

Abstract

We report the results of our intensive intranight optical monitoring of 8 `radio-intermediate quasars' (RIQs) having flat or inverted radio spectra. The monitoring was carried out in {\it R-} band on 25 nights during 2005-09. An intranight optical variability (INOV) detection threshold of $\sim$ 1--2% was achieved for the densely sampled differential light curves (DLCs). These observations amount to a large increase over those reported hitherto for this rare and sparsely studied class of quasars which can, however, play an important role in understanding the link between the dominant varieties of powerful AGN, namely the radio-quiet quasars (RQQs), radio-loud quasars (RLQs) and blazars. Despite the probable presence of relativistically boosted nuclear jets, clear evidence for INOV in our extensive observations was detected only on one night. These results demonstrate that as a class, RIQs are much less extreme in nuclear activity compared to blazars. The availability in the literature of INOV data for another 2 RIQs conforming to our selection criteria allowed us to enlarge the sample to 10 RIQs (monitored on a total of 42 nights for a minimum duration of $\sim 4$ hours per night). The absence of large amplitude INOV $(\psi >3$ persists in this enlarged sample. This extensive database has enabled us to arrive at the first estimate for the INOV Duty Cycle (DC) of RIQs. The DC is found to be small ($\sim$ 9%). The corresponding value is known to be $\sim 60$ for BL Lacs and $\approx 15$ for RLQs and RQQs. On longer-term, the RIQs are found to be fairly variable with typical amplitudes of $\approx$ 0.1-mag. The light curves of these RIQs are briefly discussed in the context of a theoretical framework proposed earlier for linking this rare kind of quasars to the much better studied dominant classes of quasars.

35 pages, 2 figures, 3 tables, accepted for publication in MNRAS

References in corpus (15)

• Five-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Cosmological Interpretation
• The Radio-Loud Fraction of Quasars is a Strong Function of Redshift and Optical Luminosity
• The VLBA Imaging and Polarimetry Survey at 5 GHz
• Accretion states and radio loudness in Active Galactic Nuclei: analogies with X-ray binaries
• High-Redshift SDSS Quasars with Weak Emission Lines
• UV Dust Attenuation in Star-forming Galaxies: II Calibrating the A(UV) vs. L_TIR/L_UV relation
• The radio structure of radio-quiet quasars
• Intra-night Optical Variability of Luminous Radio Quiet QSOs
• Extremely violent optical microvariability in blazars: fact or fiction?
• Radio Properties of Low Redshift Broad Line Active Galactic Nuclei
• The nature of the intranight variability of radio-quiet quasars
• Evidence for a population of beamed radio intermediate quasars
• A population of high-redshift type-2 quasars-II. Radio Properties
• Multiband Comparative Study of Optical Microvariability in RL vs. RQ Quasars
• The 2dF BL Lac Survey II

Cited by in corpus (9)

• Intra-night optical variability of core dominated radio quasars: the role of optical polarization
• Constraining the quasar radio-loud fraction at $z\sim 6$ with deep radio observations
• Improved characterisation of intra-night optical variability of prominent AGN classes
• Optical microvariability properties of BALQSOs
• Multi-wavelength variability study of the classical BL Lac object PKS 0735+178 on timescales ranging from decades to minutes
• Intra-Night Optical monitoring of three γ-ray detected Narrow-line Seyfert 1 galaxies
• On the photometric error calibration for the `differential light curves' of point-like Active Galactic Nuclei
• Optical Microvariability in Quasars: Spectral Variability
• Multi-epoch intra-night optical monitoring of 8 radio-quiet BL Lac candidates