IIA Institutional Repository

Browsing by Author "Wiita, P. J"

Browsing by Author "Wiita, P. J"

Sort by: Order: Results:

  • Coherent Plasma Processes and the Continuum Emission in Active Galactic Nuclei 
    Krishan, V; Wiita, P. J (Royal Astronomical Society, 1990-10)
    Stimulated Raman scattering processes appear to be able to produce the typical electromagnetic continuum of an active galactic nucleus (AGN). Seed photons beat through Raman forward-scattering to create Langmuir plasma ...
  • A comparative study of the intra-night optical variability of powerful AGNs 
    Stalin, C. S; Gopal-Krishna; Sagar, R; Wiita, P. J (Astronomical Society of India, 2002-09)
    In order to address a currently much debated issue, we are carrying out a systematic search for intra-night optical micro-variability in major classes of powerful (M'II ~ -23.0 mag) active galactic nuclei (AGNs). Our ...
  • Did Radio Galaxies Play a Major Role in the Evolution of the Universe? 
    Krishna, G; Wiita, P. J (Astronomical Society of India, 2003)
    During the `quasar era' at z ~ 2 - 3, radio galaxies had a much higher co-moving density; however, such sources are only detectable for small fractions of their active lifetimes, thanks to expansion losses and inverse ...
  • Disk luminosity and angular momentum for accreting, weak field neutron stars in the ‘Slow’ rotation approximation 
    Datta, B; Thampan, A. V; Wiita, P. J (Indian Academy of Sciences, 1995-12)
    For accretion on to neutron stars possessing weak surface magnetic fields and substantial rotation rates (corresponding to the secular instability limit), we calculate the disk and surface layer luminosities general ...
  • Effect of beam-plasma instabilities on accretion disk flares 
    Krishan, V; Wiita, P. J; Ramadurai, S (European Southern Observatory, 2000-04)
    We show that a certain class of flare models for variability from accretion disk coronae are subject to beam-plasma instabilities. These instabilities can prevent significant direct acceleration and greatly reduce the ...
  • Expansion of radio galaxies in a cosmologically evolving medium: possible implications for the cosmic star-formation history 
    Barai, P; Gopal-Krishna; Osterman, M. A; Wiita, P. J (Astronomical Society of India, 2004-12)
    We compare earlier estimates of the volumes filed by lobes of radio galaxies during the quasar era based upon non-evolving ambient media with new ones assuming a strong cosmological evolution of the ambient medium. If the ...
  • Frequency-dependent core shifts and parameter estimation for the blazar 3C 454.3 
    Mohan, Prashanth; Agarwal, A; Mangalam, A; Gupta, A. C; Wiita, P. J; Volvach, A. E; Aller, M. F; Aller, H. D; Gu, M. F; Lahteenmaki, A; Tornikoski, M; Volvach, L. N (Oxford University Press on behalf of the Royal Astronomical Society, 2015-09-11)
    We study the core shift effect in the parsec-scale jet of the blazar 3C 454.3 using the 4.8– 36.8 GHz radio light curves obtained from three decades of continuous monitoring. From a piecewise Gaussian fit to each flare, ...
  • Improved characterization of intranight optical variability of prominent AGN classes 
    Goyal, A; Gopal-Krishna; Wiita, P. J; Stalin, C. S; Sagar, R (Oxford University Press on behalf of the Royal Astronomical Society, 2013-10-21)
    The incidence of intranight optical variability (INOV) is known to differ significantly among different classes of powerful active galactic nuclei (AGN). A number of statistical methods have been employed in the literature ...
  • Intra-night optical variability of core dominated radio quasars: the role of optical polarization 
    Goyal, A; Gopal-Krishna; Wiita, P. J; Anupama, G. C; Sahu, D. K; Sagar, R; Joshi, S (EDP Sciences, 2012-08)
    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. ...
  • Intranight optical monitoring of optically selected bright quasars 
    Sagar, R; Gopal-Krishna; Wiita, P. J (Royal Astronomical Society, 1996-08)
    As part of an ongoing programme to search for intranight optical variations, we report results for six radio-quiet and one radio-moderate, but all optically bright and luminous, quasi-stellar objects (QSOs), using the ...
  • Microflares in accretion disks 
    Krishan, V; Ramadurai, S; Wiita, P. J (The European Southern Observatory, 2003-02)
    We have investigated the phenomenon of explosive chromospheric evaporation from an accretion disk as a mechanism for fast variability in accreting sources such as low mass X-ray binaries and active galactic nuclei. This ...
  • Multiwavelength intraday variability of the BL Lacertae S5 0716+714 
    Gupta, A. C; Krichbaum, T. P; Wiita, P. J; Rani, B; Sokolovsky, K. V; Mohan, Prashanth; Mangalam, A; Marchili, N; Fuhrmann, L; Agudo, I; Bach, U; Bachev, R; Böttcher, M; Gabanyi, K. E; Gaur, H; Hawkins, K; Kimeridze, G. N; Kurtanidze, O. M; Kurtanidze, S. O; Lee, C.-U; Liu, X; McBreen, B; Nesci, R; Nestoras, G; Nikolashvili, M. G; Ohlert, J. M; Palma, N; Peneva, S; Pursimo, T; Semkov, E; Strigachev, A; Webb, J. R; Wiesemeyer, H; Zensus, J. A (Wiley-Blackwell, 2012-09)
    We report results from a one-week multiwavelength campaign to monitor the BL Lacertae object (BL Lac) S5 0716+714 (on 2009 December 9–16). Nine ground-based telescopes at widely separated longitudes and one space-based ...
  • Near-infrared and optical imaging of Q2345+007: The largest gravitationally lensed QSO system? 
    Gopal-Krishna; Yates, M; Wiita, P. J; Smette, A; Pati, A. K; Altieri, B (The European Southern Observatory, 1993-12)
    We have taken K, R, V, and B band images of Q 2345+007, which has been claimed to be the gravitationally lensed quasar with the widest separation between the two images (approximately equal 7 arcsec), although the lens ...
  • Optical microvariability in radio quiet quasars 
    Wiita, P. J; Gopal-Krishna; Sagar, R (Kluwer Academic Publishers, 1994)
    We have observed 11 radio quiet QSOs (RQQSOs) to see if they exhibit intranight variability in the optical. The detection of such microvariability would support models in which flutuations on accretion disks are dominant, ...
  • Rapid optical variability of TeV blazars 
    Gopal-Krishna; Goyal, A; Joshi, S; Karthick, C; Sagar, R; Wiita, P. J; Anupama, G. C; Sahu, D. K (Wiley-Blackwell, 2011-09)
    In this first systematic attempt to characterize the intranight optical variability (INOV) of TeV-detected blazars, we have monitored a well-defined set of nine TeV blazars on total 26 nights during 2004–10. In this R- or ...
  • Relativistic beams, thick accretion disks and active galactic nuclei 
    Wiita, P. J; Kapahi, V. K; Saikia, D. J (Astronomical Society of India, 1982-12)
    We review recent analyses of observations of radio galaxies and quasars that support the relativistic beaming models and appear to produce values for the Lorentz factors of the radiating mateiral in the nuclear jets. Thick ...
  • Stellar Disruption by Supermassive Black Holes and the Quasar Radio Loudness Dichotomy 
    Gopal-Krishna; Mangalam, A; Wiita, P. J (The American Astronomical Society, 2008-06-10)
    The origin of the dichotomy of radio loudness among quasars can be explained using recent findings that the mass of the central supermassive black hole (SMBH) in extended radio-loud quasars is systematically a few times ...
  • Stimulated raman scattering in active galactic nuclei 
    Krishan, V; Wiita, P. J (International Astronomical Union, 1986)
    Stimulated Raman Scattering (SRS) processes offer an attractive and efficient method for producing both essentially the entire non-thermal continuum as well as fast electrons in active galactic nuclei (AGN). In this picture, ...
  • Stochastic modeling of multiwavelength variability of the classical BL Lac Object OJ 287 on timescales ranging from decades to hours 
    Goyal, A; Stawarz, L; Zola, S; Marchenko, V; Soida, M; Nilsson, K; Ciprini, S; Baran, A; Ostrowski, M; Wiita, P. J; Gopal-Krishna; iemiginowska, A; Sobolewska, M; Jorstad, S; Marscher, A; Aller, M. F; Aller, H. D; Hovatta, T; Caton, D. B; Reichart, D; Matsumoto, K; Sadakane, K; Gazeas, K; Kidger, M; Piirola, V; Jermak, H; Alicavus, F; Baliyan, K. S; Baransky, A; Berdyugin, A; Blay, P; Boumis, P; Boyd, D; Bufan, Y; Campas Torrent, M; Campos, F; Carrillo Gomez, J; Dalessio, J; Debski, B; Dimitrov, D; Drozdz, M; Er, H; Erdem, A; Escartin Perez, A; Fallah Ramazani, V; Filippenko, A. V; Gafton, E; Garcia, F; Godunova, V; Gomez Pinilla, F; Maheswar, G; Haislip, J. B; Haque, S; Harmanen, J; Hudec, R; Hurst, G; Ivarsen, K. M; Joshi, A; Kagitani, M; Karaman, N; Karjalainen, R; Kaur, N; Koziel-Wierzbowska, D; Kuligowska, E; Kundera, T; Kurowski, S; Kvammen, A; LaCluyze, A. P; Lee, B. C; Liakos, A; Lozano de Haro, J; Moore, J. P; Mugrauer, M; Naves Nogues, R; Neely, A. W; Ogloza, W; Okano, S; Pajdosz, U; Pandey, J. C; Perri, M; Poyner, G; Provencal, J; Pursimo, T; Raj, A; and 29 co-authors (IOP Publishing, 2018-08-20)
    We present the results of our power spectral density analysis for the BL Lac object OJ 287, utilizing the Fermi-LAT survey at high-energy γ-rays, Swift-XRT in X-rays, several ground-based telescopes and the Kepler satellite ...
  • Testing the mechanisms for optical micro-variability of powerful active galactic nuclei 
    Gopal-Krishna; Sagar, R; Wiita, P. J (Astronomical Society of India, 1993)
    We present the first results of a new type of observational program being carried out using the 2.34m Vainu Bappu Telescope at Kavalur. This program involves intra-night optical monitoring of radio quiet but optically ...

Search DSpace

Browse

My Account