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Browsing by Author "Wiita, P. J."

Browsing by Author "Wiita, P. J."

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  • A ∼4.6 h quasi-periodic oscillation in the BL Lacertae PKS 2155-304? 
    Lachowicz, P.; Gupta, A. C.; Gaur, H.; Wiita, P. J. (2009)
    We report a possible detection of an ̴4.6-h quasi-periodic oscillation (QPO) in the 0.3–10 keV emission of the high-energy peaked blazar PKS 2155−304 from a 64 ks observation by the XMM-Newton EPIC/pn detector. We identify ...
  • Anti-correlated optical flux and polarization variability in BL Lac 
    Gaur, Haritma; Gupta, A. C.; Wiita, P. J.; Uemura, M.; Itoh, R.; Sasada, M. (2014)
    We present the results of photometric (V band) and polarimetric observations of the blazar BL Lac during 2008–2010 using TRISPEC attached to the KANATA 1.5 m telescope in Japan. The data reveal a great deal of variability ranging ...
  • A comparative study of the intra-night optical variability of powerful AGNs 
    Stalin, C. S.; Gopal-Krishna; Sagar, R.; Wiita, P. J. (2002)
    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 (Mᵥ ≥ -23.0 mag)active galactic nuclei (AGNs). Our sample ...
  • Detection of intre-day variability timescales of four high-energy peaked blazars with XMM- newton 
    Gaur, H.; Gupta, A. C.; Lachowicz, P.; Wiita, P. J. (2010)
    We selected a sample of 24 XMM–Newton light curves (LCs) of four high energy peaked blazars, PKS 0548−322, ON 231, 1ES 1426+428, and PKS 2155−304. These data comprise continuous LCs of 7.67–18.97 hr in length. We searched ...
  • Intranight optical variability of BL Lacs, radio-quiet quasars and radio-loud quasars 
    Stalin, C. S.; Gupta, A. C.; Gopal-Krishna; Wiita, P. J.; Sagar, R. (2005)
    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 ...
  • Intranight optical variability of blazers 
    Sagar, R.; Stalin, C. S.; Gopal-Krishna; Wiita, P. J. (2004)
    We present results of a multi-epoch intranight optical monitoring of 11 blazars consisting of six BL Lac objects and five radio core-dominated quasars (CDQs). These densely sampled and sensitive R-band CCD observations, ...
  • Intranight optical variability of radio-quiet and radio lobe dominated quasars 
    Stalin, C. S.; Gopal-Krishna; Sagar, R.; Wiita, P. J. (2004)
    We present results of a programme of multi-epoch, intranight optical monitoring of a sample of non-blazar-type active galactic nuclei (AGN), which includes seven radio-quiet quasars (RQQs) and an equal number of radio-loud, ...
  • Multiband optical monitoring of the blazars S5 0716+714 and BL Lacertae 
    Stalin, C. S.; Gopal-Krishna; Sagar, R.; Wiita, P. J.; Mohan, V.; Pandey, A. K. (2006)
    We report the results of multiband optical photometric monitoring of two well-known blazars, S5 0716+714 and BL Lacertae, carried out during 1996 and 2000–01 with an aim to study optical variations on time-scales ranging ...
  • Multiwavelength variability of the blazars Mrk 421 and 3c 454.3 in the high state 
    Gaur, Haritma; Gupta, A. C.; Wiita, P. J. (2012)
    We report the results of photometric observations of the blazars Mrk 421 and 3C 454.3 designed to search for intraday variability (IDV) and short-term variability (STV). Optical photometric observations were spread over 18 ...
  • Nearly periodic fluctuations in the long-term x-ray light curves of the blazars AO 0235+164 and 1ES 2321+419 
    Rani, B.; Wiita, P. J.; Gupta, A. C. (2009-05-10)
    We have performed a structure function analysis of the Rossi X-Ray Timing Explorer All-Sky Monitor data to search for variability in 24 blazars using data trains that each exceed 12 yr. Although 20 of them show nominal periods ...
  • Optical intraday variability studies of 10 low energy peaked blazars 
    Rani, B.; Gupta, A. C.; Joshi, U. C.; Ganesh, S.; Wiita, P. J. (2011)
    We have carried out optical (R band) intraday variability (IDV) monitoring of a sample of 10 bright low energy peaked blazars (LBLs). 40 photometric observations, of an average of ∼4 h each, were made between 2008 September ...
  • Optical microvariability properties of BALQSOs 
    Joshi, R.; Chand, H.; Gupta, A. C.; Wiita, P. J. (2011)
    We present optical light curves of 19 radio-quiet (RQ) broad absorption line (BAL) quasi-stellar objects (QSOs) and study their rapid variability characteristics. Systematic CCD observations, aided by a careful data ...
  • Optical variability of radio-intermediate quasars 
    Goyal, A.; Krishna-Gopal; Joshi, S.; Sagar, R.; Wiita, P. J.; Anupama, G. C. (2010)
    We report the results of our intensive intranight optical monitoring of eight optically bright ‘radio-intermediate quasars’ (RIQs) having flat or inverted radio spectra. The monitoring was carried out in R band on ...
  • Periodic oscillations in the intra-day optical light curves of the blazar S5 0716+714 
    Gupta, A. C.; Srivastava, A. K.; Wiita, P. J. (2009-01-01)
    We present the results of a periodicity search of 20 intra-day variable optical light curves of the blazar S5 0716+714, selected from a database of 102 light curves spanning over three years. We use a wavelet analysis technique ...
  • Probing spectral properties of radio-quiet quasars searched for optical microvariability 
    Chand, H.; Wiita, P. J.; Gupta, A. C. (2010)
    We obtained Sloan Digital Sky Survey spectra for a set of 37 radio-quiet quasars [(radio-quiet quasi-stellar objects (RQQSOs)] that had been previously examined for rapid small-scale optical variations, or microvariability. ...
  • Probing spectral properties of radio-quiet quasars searched for optical microvariability – II 
    Joshi, R.; Chand, H.; Wiita, P. J.; Gupta, A. C.; Srianand, R. (2012)
    In the context of active galactic nucleus (AGN) unification schemes, rapid variability properties play an important role in understanding any intrinsic differences between sources in different classes. In this respect, any ...
  • Quasi-periodic oscillations of ~15 minutes in the optical light curve of the BL Lac S5 0716+714 
    Rani, B.; Gupta, A. C.; Joshi, U. C.; Ganesh, S.; Wiita, P. J. (2010)
    Over the course of 3 hr on 2008 December 27, we obtained optical (R band) observations of the blazar S5 0716+714 at a very fast cadence of 10 s. Using several different techniques, we find fluctuations with an approximately ...
  • Rapid optical variability in radio-quiet QSOs 
    Gopal-Krishna; Gupta, A. C.; Sagar, R.; Wiita, P. J.; Chaubey, U. S.; Stalin, C. S. (2000)
    We report results of the observations at the Vainu Bappu Observatory and the Uttar Pradesh State Observatory of eight radio-quiet quasi-stellar objects (RQQSOs) during 1996-99. This is a part of our ongoing programme to ...
  • 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. (2011)
    In this first systematic attempt to characterize the intranight optical variability (INOV) of TeVdetected blazars, we have monitored a well-defined set of nine TeV blazars on total 26 nights during 2004–10. In this R- or ...
  • Variability of spectral snergy distribution of Blazar S5 0716+714 
    Rani, B.; Gupta, A. C.; Wiita, P. J. (2011)
    The emission from blazars is known to be variable at all wavelengths.The flux variability is often accompanied by spectral changes. Spectral energy distribution (SED) changes must be associated with changes in the spectra ...

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