The WEBT BL Lacertae Campaign 2001 and its 
extension

Villata, M.; Raiteri, C. M.; Kurtanidze, O. M.; Nikolashvili, M. G.; Ibrahimov, M.; Papadakis, I. E.; Tosti, G.; Hroch, Filip; Takalo, L. O.; Sillanpää, A.; Hagen-Thorn, V. A.; Larionov, V. M.; Schwartz, Richard D.; Basler, Joseph W.; Brown, L. F.; Balonek, T. J.; Benítez, E.; Ramirez, A.; Sadun, A. C.; Boltwood, P.; Carini, M. T.; Barnaby, D.; Coloma, J. M.; Ros, Javier; Dai, B. Z.; Xie, Gaogang; Mattox, J. R.; Rodríguez, D.; Asfandiyarov, I. M.; Atkerson, A.; Beem, J. L.; Bloom, S. D.; Chanturiya, S. M.; Ciprini, S.; Crapanzano, S.; Diego, J. A. de; Ефимова, Н. В.; Gardiol, D.; Guerra, J.; Kahharov, B. B.; Kapanadze, Bidzina; Karttunen, Hannu; Katô, Takeo; Kimeridze, G. N.; Kudryavtseva, N. A.; Lainela, M.; Lanteri, L.; Ларионова, Е. Г.; Maesano, M.; Marchili, N.; Massone, G.; Monroe, TalaWanda R.; Montagni, F.; Nesci, R.; Nilsson, K.; Noble, J. C.; Nucciarelli, G.; Ostorero, L.; Papamastorakis, J.; Pasanen, M.; Peters, C. S.; Pursimo, T.; Reig, P.; Ryle, W. T.; Sclavi, S.; Sigua, L. A.; Uemura, Makoto; Wills, W.

doi:10.1051/0004-6361:20035895

Cited by 123 publications

(108 citation statements)

References 18 publications

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“…The BWB trend has been found to be predominant in BL Lacertae by all optical observations of this source till date during both flaring and steady states (Ghosh et al 2000;Gu et al 2006) which was revealed by our observations also. Villata et al (2004b) found that the intraday flares followed BWB trend strongly with a slope of ∼ 0.4 which is also the case for our data with the slopes of the intra-night LCs more than ∼ 0.4 in majority of cases. Thus, our colour variability results for the source being strongly chromatic between Oct -Nov 2014 were consistent with those of Villata et al (2004b).…”

Section: Colour-magnitude Relationshipsupporting

confidence: 89%

“…Villata et al (2004b) found that the intraday flares followed BWB trend strongly with a slope of ∼ 0.4 which is also the case for our data with the slopes of the intra-night LCs more than ∼ 0.4 in majority of cases. Thus, our colour variability results for the source being strongly chromatic between Oct -Nov 2014 were consistent with those of Villata et al (2004b). Since the jet emissions are completely dominating the flux from BL Lacerate objects, this can be explained by the shock-in-jet models elaborated under section 8.…”

Section: Colour-magnitude Relationshipsupporting

confidence: 89%

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Multiband optical variability studies of BL Lacertae

Agarwal¹,

Gupta²

2015

Monthly Notices of the Royal Astronomical Society

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We monitored BL Lacertae for 13 nights in optical B, V, R, and I bands during October and November 2014 including quasi-simultaneous observations in V and R bands using two optical telescopes in India. We have studied multi-band optical flux variations, colour variation and spectral changes in this blazar. Source was found to be active during the whole monitoring period and showed significant intraday variability on 3 nights in V and R filters while displayed hints of variability on 6 other dates in R passband and on 2 nights in V filter. From the colour-magnitude analysis of the source we found that the spectra of the target gets flatter as it becomes brighter on intra-night timescale. Using discrete correlation technique, we found that intraday light curves in both V and R filters are almost consistent and well correlated with each other. We also generated spectral energy distribution (SED) of the target using the B, V, R, and I data sets for all 13 nights which could help us investigate the physical process responsible for the observed variations in BL Lacertae objects. We also discuss possible physical causes of the observed spectral variability.

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Section: Colour-magnitude Relationshipsupporting

confidence: 89%

Section: Colour-magnitude Relationshipsupporting

confidence: 89%

Multiband optical variability studies of BL Lacertae

Agarwal¹,

Gupta²

2015

Monthly Notices of the Royal Astronomical Society

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“…The minimum Doppler factor of 11, corresponding to a maximum angle of about 5.0 • , was reached during the flux minima. The above picture would explain the long/midterm flux variations (see also Villata et al 2002Villata et al , 2004, while the short-term flares (see below) would be due either to perturbations moving downstream in the jet or to a finer geometrical structure, as proposed for BL Lacertae by Larionov et al (2010).…”

Section: Flux Correlationsmentioning

confidence: 86%

The long-lasting activity of 3C 454.3

Raiteri

Villata

Aller

et al. 2011

A&A

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Context. The blazar 3C 454.3 is one of the most active sources from the radio to the γ-ray frequencies observed in the past few years. Aims. We present multiwavelength observations of this source from April 2008 to March 2010. The radio to optical data are mostly from the GASP-WEBT, UV and X-ray data from Swift, and γ-ray data from the AGILE and Fermi satellites. The aim is to understand the connection among emissions at different frequencies and to derive information on the emitting jet. Methods. Light curves in 18 bands were carefully assembled to study flux variability correlations. We improved the calibration of optical-UV data from the UVOT and OM instruments and estimated the Lyα flux to disentangle the contributions from different components in this spectral region. Results. The observations reveal prominent variability above 8 GHz. In the optical-UV band, the variability amplitude decreases with increasing frequency due to a steadier radiation from both a broad line region and an accretion disc. The optical flux reaches nearly the same levels in the 2008-2009 and 2009-2010 observing seasons; the mm one shows similar behaviour, whereas the γ and X-ray flux levels rise in the second period. Two prominent γ-ray flares in mid 2008 and late 2009 show a double-peaked structure, with a variable γ/optical flux ratio. The X-ray flux variations seem to follow the γ-ray and optical ones by about 0.5 and 1 d, respectively. Conclusions. We interpret the multifrequency behaviour in terms of an inhomogeneous curved jet, where synchrotron radiation of increasing wavelength is produced in progressively outer and wider jet regions, which can change their orientation in time. In particular, we assume that the long-term variability is due to this geometrical effect. By combining the optical and mm light curves to fit the γ and X-ray ones, we find that the γ (X-ray) emission may be explained by inverse-Comptonisation of synchrotron optical (IR) photons by their parent relativistic electrons (SSC process). A slight, variable misalignment between the synchrotron and Comptonisation zones would explain the increased γ and X-ray flux levels in 2009-2010, as well as the change in the γ/optical flux ratio during the outbursts peaks. The time delays of the X-ray flux changes after the γ, and optical ones are consistent with the proposed scenario.

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“…from minutes to years timescales (e.g. 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.…”

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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The WEBT BL Lacertae Campaign 2001 and its extension

Cited by 123 publications

References 18 publications

Multiband optical variability studies of BL Lacertae

Multiband optical variability studies of BL Lacertae

The long-lasting activity of 3C 454.3

Core shift effect in blazars

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