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

Department of Physics and Astronomy, Georgia State University, Atlanta, Georgia, United States
Monthly Notices of the Royal Astronomical Society (Impact Factor: 5.11). 12/2004; 356(2):607 - 614. DOI: 10.1111/j.1365-2966.2004.08473.x
Source: arXiv


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.

Download full-text


Available from: Paul J. Wiita, Jul 29, 2015
10 Reads
  • Source
    • "At the same time, the interband relations might be very complex and sometimes can not be explained by the reprocessing model alone. Other mechanisms, such as accretion disc instabilities which can drive the X-ray variations via Comptonisation, the presence of a weak blazar component (see [8] [9]) or disc fluctuations drifting inward [4] are also considered to explain the multiwavelength correlations. Thus, the observed correlations between different bands and interband time delays can give important constraints on the origin of AGN variability. "
    [Show abstract] [Hide abstract]
    ABSTRACT: The time delays between brightness variations in different optical bands have been measured for a large number of Seyfert galaxies and low-redshift quasars. These time delays represent the travel time of light between different emission regions of the source and can be used to test variability scenarios. Based on multiwavelength observations of the lensed quasars: Q2237+0305, SBS1520+530, HE2149-2745, HE1104-1805 and UM673, we explore a variability mechanism in the redshift range 1.4 z 2.7 . From cross-correlation analysis of the light curves of the quasars we find that the brightness variations at longer wavelengths may follow the brightness variations at shorter wavelengths by a few days. An independent analysis of the multiband light curves of nonlensed quasars from the same redshift interval confirms the evidence of a time delay. A comparison of the observed time delays with the delays expected from a model of an accretion disc irradiated by the central variable source shows that reprocessing might be the primary mechanism responsible for the observed variability on the considered timescales.
    The Open Astronomy Journal 01/2010; 3(1):184-192. DOI:10.2174/1874381101003010184
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Most of the matter in the Universe appears to be in some form which does not emit or absorb light. While evidence for the existence of this dark matter has accumulated over the last seventy years, its nature remains elusive. In this thesis, quasars and low surface brightness galaxies (LSBGs) are used to investigate the properties of the dark matter. Quasars are extremely bright light sources which can be seen over vast distances. These cosmic beacons may be used to constrain dark matter in the form of low-mass, compact objects along the line of sight, as such objects are expected to induce brightness fluctuations in quasars through gravitational microlensing effects. Using a numerical microlensing model, we demonstrate that the uncertainty in the typical size of the optical continuum-emitting region in quasars represents the main obstacle in this procedure. We also show that, contrary to claims in the literature, microlensing fails to explain the observed long-term optical variability of quasars. Here, quasar distances are inferred from their redshifts, which are assumed to stem from the expansion of the Universe. Some astronomers do however defend the view that quasar redshifts could have a different origin. A number of potential methods for falsifying claims of such non-cosmological redshifts are proposed. As the ratio of dark to luminous matter is known to be unusually high in LSBGs, these objects have become the prime targets for probing dark matter halos around galaxies. Here, we use spectral evolutionary models to constrain the properties of the stellar populations in a class of unusually blue LSBGs. Using rotation curve data obtained at the ESO Very Large Telescope, we also investigate the density profiles of their dark halos. We find our measurements to be inconsistent with the predictions of the currently favoured cold dark matter scenario.
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: We present the results of a systematic observational campaign designed to search for microvariability in the optical polarization of BL Lac objects. We have observed a sample formed by 8 X-ray-selected and 10 radio-selected sources, looking for rapid changes in both the degree of linear polarization and the corresponding polarization angle. The whole campaign was carried out along the last three years, and most of the objects were observed at least on two consecutive nights. The statistical properties of both classes of BL Lac objects are compared, and some general conclusions on the nature of the phenomenon are drawn. In general, radio selected sources seem to display higher duty cycles for polarimetric microvariability and, on average, they have a stronger polarization. Comment: 12 pages, 15 figures, accepted for publication in A&A
    Astronomy and Astrophysics 06/2005; 442(1). DOI:10.1051/0004-6361:20053325 · 4.38 Impact Factor
Show more