Optical observations of 22 violently variable extragalactic sources - 1968-1986

Webb, J. R.; Smith, Alex; Leacock, R. J.; Fitzgibbons, G. L.; Gombola, P. P.; Shepherd, David W.

doi:10.1086/114641

Cited by 179 publications

(150 citation statements)

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“…In this light curve the minimum value is B = 16.7 in the late sixties. Webb et al (1988) report a long record of observations from 1971 to 1985, somehow continuing the sequence of Shen and Usher: their minimum value is B = 17.17 on Jan.-3-1981 and the median value on 1981 is B ∼ 16.5 very similar to our finding. Also Xie et al (1987) report B between 16.3 and 17.1 on Sep.-Nov. 1981, while Shokin et al (1994) found BL Lac at m pg 16.7 on 1992-Aug.-24.…”

Section: Discussionsupporting

confidence: 89%

BVRI photometry of BL Lacertae in 1993-1995

Maesano

Montagni

Massaro

et al. 1997

Astron. Astrophys. Suppl. Ser.

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Abstract. The results of optical photometry of BL Lac over a time interval of two years in the B, V, R, I filters are presented. The source is found for most of the time in a low state. The mean colour indexes are similar to those observed in higher luminosity states, however a flattening of the spectral slope was present during three small amplitude outbursts. A brief comparison with the observations available in the literature and some considerations on the physical conditions driving the appearance of emission lines are made.

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Section: Discussionsupporting

confidence: 89%

BVRI photometry of BL Lacertae in 1993-1995

Maesano

Montagni

Massaro

et al. 1997

Astron. Astrophys. Suppl. Ser.

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“…The time scales of these outbursts are different: from an entire season to several days, the minimum timescale to which our observations are sensitive. Such behaviour in the flux variations of BL Lac has been described many times (e.g., Webb et al 1988;Hagen-Thorn et al 1997).…”

Section: The General Properties Of the Point Sourcementioning

confidence: 81%

Analysis of the long-term polarization behaviour of BL Lac

Hagen-Thorn

Ларионова

Jorstad

et al. 2002

A&A

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Abstract. An analysis is performed of polarimetric and photometric observations of BL Lac carried out in 1969-1991 at the Astronomical Institute of St. Petersburg State University. The distribution of polarization directions certainly points to the existence of the preferred direction of polarization (θ = 22 • ) close to the direction of the jet observed by VLBI. High polarization degree and colorimetric data are evidence of the synchrotron nature of the variable source. The relative Stokes parameters are distributed normally over some mean value. The correlations between different parameters characterizing the flux density and polarization of the central point source allow us to consider that in BL Lac there is a continually acting source of polarized radiation on which the sources with randomly distributed polarization directions are superimposed.

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“…Villata et al 2004;Agarwal & Gupta 2015). From ∼ 15 years of variability observations (June 1971 to January 1985), Webb et al (1988) inferred recurrent variations after every 0.31, 0.60, and 0.88 yr using the Fourier periodogram. Marchenko et al (1996) found a statistically significant long term component with P = 7.8 ± 0.2 yr in the 20 year duration light curve using the whitening of the time series method.…”

Section: Bl Lacertaementioning

confidence: 99%

Core shift effect in blazars

Agarwal

Mohan

Gupta

et al. 2017

Monthly Notices of the Royal Astronomical Society

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We studied the pc-scale core shift effect using radio light curves for three blazars, S5 0716+714, 3C 279 and BL Lacertae, which were monitored at five frequencies (ν) between 4.8 GHz and 36.8 GHz using the University of Michigan Radio Astronomical Observatory (UMRAO), the Crimean Astrophysical Observatory (CrAO), and Metsahovi Radio Observatory for over 40 years. Flares were Gaussian fitted to derive time delays between observed frequencies for each flare (∆t), peak amplitude (A), and their half width. Using A ∝ ν α we infer α in the range −16.67 to 2.41 and using ∆t ∝ ν 1/kr , we infer k r ∼ 1, employed in the context of equipartition between magnetic and kinetic energy density for parameter estimation. From the estimated core position offset (Ω rν ) and the core radius (r core ), we infer that opacity model may not be valid in all cases. The mean magnetic field strength at 1 pc (B 1 ) and at the core (B core ), are in agreement with previous estimates. We apply the magnetically arrested disk model to estimate black hole spins in the range 0.15 − 0.9 for these blazars, indicating that the model is consistent with expected accretion mode in such sources. The power law shaped power spectral density has slopes −1.3 to −2.3 and is interpreted in terms of multiple shocks or magnetic instabilities.

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Optical observations of 22 violently variable extragalactic sources - 1968-1986

Cited by 179 publications

References 0 publications

BVRI photometry of BL Lacertae in 1993-1995

BVRI photometry of BL Lacertae in 1993-1995

Analysis of the long-term polarization behaviour of BL Lac

Core shift effect in blazars

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