Timescales of Long-Term Optical Base-Level Fluctuations in Three Classes of AGN

Smith, Alex; Nair, A. D.

doi:10.1086/133634

Cited by 42 publications

(35 citation statements)

References 16 publications

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“…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. Smith & Nair (1995) found a period of 7.7 yr using a 20 yr duration light curve using Fourier analysis thus, consistent with Marchenko et al (1996). Later, Fan et al (1998) obtained a long term period of 14 yr using the Jurkevich method on the optical light curve.…”

Section: Bl Lacertaesupporting

confidence: 88%

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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Section: Bl Lacertaesupporting

confidence: 88%

Core shift effect in blazars

Agarwal

Mohan

Gupta

et al. 2017

Monthly Notices of the Royal Astronomical Society

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“…After the deep minimum observed in 1972-74, the brightness of ON 231 began to increase following a slow, quasi linear trend, with a small outburst visible in the period 1979-1981. Superimposed on this trend there are complex variations characterized by a total amplitude of about one magnitude and a time scale of about 4 years (Smith & Nair 1995). From a visual inspection of the historic light curve, Pollock (1974) suggested a possible quasi-periodicity of about 14 years for the outbursts, a value which agrees with the period of 13.6 ± 1.3 years recently proposed by Liu et al (1995).…”

Section: The Historical Light Curve Of On 231supporting

confidence: 61%

“…It is known that the source shows variability on time scales from hours to years (see, e.g., Smith & Nair 1995;Xie et al 1992). But previously published light curves are not so densely sampled to allow a sufficiently detailed study of structure and occurrence of the short term variations.…”

Section: Introductionmentioning

confidence: 99%

$BVR_{\rm c}I_{\rm c}$ monitoring of ON 231 during the great outburst in 1994-1997

Tosti

Fiorucci

Luciani

et al. 1998

Astron. Astrophys. Suppl. Ser.

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Abstract. We present the most continuous data base of optical multiband data ever published on the BL Lacertae object ON 231 (W Com). The data have been collected during an intensive and coordinated BV R c I c monitoring campaign carried out in the period from March 1994 to March 1997. During our campaign, the source brightness was at the highest level ever observed. The light curve shows a complex structure, characterized by the presence of three major outbursts having the observed maxima in March 1995, February 1996, and January 1997, when ON 231 reached its historical maximum (B 14.2). Variability on time scales from a few hours up to a month have frequently been observed and the light curve seems to be the superposition of many flares with different amplitudes and time scales. The broad-band optical spectral energy distribution is characterized by a spectral slope which correlates with the flux level. In particular, the higher is the flux the flatter is the spectrum.

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“…Note that some other BL Lac objects (e.g. 0215 + 015), for which detections of broad emission lines have been reported, are similarly characterized by long term decreasing luminosity trends (Smith & Nair 1995). A spectroscopic monitoring of this object, as well as of other blazars in a low state, would be highly useful to clarify the relation of the line emission with the variations of the ionizing continuum.…”

Section: Discussionmentioning

confidence: 77%

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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Timescales of Long-Term Optical Base-Level Fluctuations in Three Classes of AGN

Cited by 42 publications

References 16 publications

Core shift effect in blazars

Core shift effect in blazars

$BVR_{\rm c}I_{\rm c}$ monitoring of ON 231 during the great outburst in 1994-1997

BVRI photometry of BL Lacertae in 1993-1995

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