The WEBT campaigns on BL Lacertae

Villata, M.; Raiteri, C. M.; Aller, H. D.; Aller, M. F.; Teräsranta, H.; Koivula, P.; Wiren, S.; 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.

doi:10.1051/0004-6361:20040439

Cited by 94 publications

(80 citation statements)

References 26 publications

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“…When the variable component dominates we get a chromatic behaviours. Villata et al (2004a) confirmed that the optical variations on short timescales can be interpreted due to strongly chromatic component while the longer timescale component as mildly chromatic component. The BWB trend could be explained by one component synchrotron model which tells that more intense the energy release, the higher the particular frequency (Fiorucci, Ciprini, & Tostiet al 2004) or due to the Doppler factor variations in a spectrum deviating from power law.…”

Section: Discussionsupporting

confidence: 57%

“…Authors also detected hints of bluer-whenbrighter (BWB) trend but any relation between spectral and flux changes were absent. Later, Villata et al (2002Villata et al ( , 2004a confirmed the presence of BWB trend in short isolated outburst but not on long timescales for BL Lacertae, indicating two different components are operating. Heidt & Wagner (1996) found 80% of complete BL Lacerate objects to show IDV confirming it to be their intrinsic nature.…”

Section: Introductionmentioning

confidence: 92%

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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: Discussionsupporting

confidence: 57%

Section: Introductionmentioning

confidence: 92%

Multiband optical variability studies of BL Lacertae

Agarwal¹,

Gupta²

2015

Monthly Notices of the Royal Astronomical Society

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“…The correlation between optical and radio flux variations in BL Lacertae has been the subject of several studies, and most of them found a correlation with a long time delay (a few months) of the radio after the optical flux changes (see e.g. Hufnagel & Bregman 1992;Tornikoski et al 1994b;Clements et al 1995;Villata et al 2004a;Bach et al 2006;Villata et al 2009b). However, simultaneous variations have already been found (Tornikoski et al 1994a).…”

Section: Optical and Near-infraredmentioning

confidence: 99%

“…1 http://www.oato.inaf.it/blazars/webt/ results have been published by Villata et al (2002), Ravasio et al (2002), Böttcher et al (2003), Villata et al (2004b), Villata et al (2004a), Bach et al (2006), Papadakis et al (2007), Villata et al (2009b), Larionov et al (2010).…”

Section: Introductionmentioning

confidence: 99%

Another look at the BL Lacertae flux and spectral variability

Raiteri

Villata

Bruschini

et al. 2010

A&A

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Aims. In a previous study we suggested that the broad-band emission and variability properties of BL Lacertae can be accounted for by a double synchrotron emission component with related inverse-Compton emission from the jet, plus thermal radiation from the accretion disc. Here we investigate the matter with further data extending over a wider energy range. Methods. The GLAST-AGILE Support Program (GASP) of the whole earth blazar telescope (WEBT) monitored BL Lacertae in 2008-2009 at radio, near-IR, and optical frequencies to follow its flux behaviour. During this period, high-energy observations were performed by XMM-Newton, Swift, and Fermi. We analyse these data with particular attention to the calibration of Swift UV data, and apply a helical jet model to interpret the source broad-band variability.Results. The GASP-WEBT observations show an optical flare in 2008 February-March, and oscillations of several tenths of mag on a few-day time scale afterwards. The radio flux is only mildly variable. The UV data from both XMM-Newton and Swift seem to confirm a UV excess that is likely caused by thermal emission from the accretion disc. The X-ray data from XMM-Newton indicate a strongly concave spectrum, as well as moderate (∼4-7%) flux variability on an hour time scale. The Swift X-ray data reveal fast (interday) flux changes, not correlated with those observed at lower energies. We compare the spectral energy distribution (SED) corresponding to the 2008 low-brightness state, which was characterised by a synchrotron dominance, to the 1997 outburst state, where the inverse-Compton emission was prevailing. A fit with an inhomogeneous helical jet model suggests that two synchrotron components are at work with their self inverse-Compton emission. Most likely, they represent the radiation from two distinct emitting regions in the jet. We show that the difference between the source SEDs in 2008 and 1997 can be explained in terms of pure geometrical variations. The outburst state occurred when the jet-emitting regions were better aligned with the line of sight, producing an increase of the Doppler beaming factor. Conclusions. Our analysis demonstrates that the jet geometry can play an extremely important role in the BL Lacertae flux and spectral variability. Indeed, the emitting jet is probably a bent and dynamic structure, and hence changes in the emitting regions viewing angles are likely to happen, with strong consequences on the source multiwavelength behaviour.

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“…In the radio band, it is a kpc-scale core halo and has a VLBI core jet to the south. The radio emission varies at higher frequencies, leading the lower-frequency emissions by several days to a few months (Villata et al 2004), and the optical variations lead the 15 GHz radio emissions by ∼100 days (Bach et al 2006). …”

Section: B0925 + 504 2fgl J09295 + 5009 (Isp Bl)mentioning

confidence: 99%

Radio and optical intra-day variability observations of five blazars

Liu

Yang

Liu

et al. 2017

Monthly Notices of the Royal Astronomical Society

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We carried out a pilot campaign of radio and optical band intra-day variability (IDV) observations of five blazars (3C66A, S5 0716+714, OJ287, B0925+504, and BL Lacertae) on December 18-21, 2015 by using the radio telescope in Effelsberg (Germany) and several optical telescopes in Asia, Europe, and America. After calibration, the light curves from both 5 GHz radio band and the optical R band were obtained, although the data were not smoothly sampled over the sampling period of about four days. We tentatively analyse the amplitudes and time scales of the variabilities, and any possible periodicity. The blazars vary significantly in the radio (except 3C66A and BL Lacertae with only marginal variations) and optical bands on intra-and inter-day time scales, and the source B0925+504 exhibits a strong quasi-periodic radio variability. No significant correlation between the radio-and optical-band variability appears in the five sources, which we attribute to the radio IDV being dominated by interstellar scintillation whereas the optical variability comes from the source itself. However, the radio-and optical-band variations appear to be weakly correlated in some sources and should be investigated based on well-sampled data from future observations.

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The WEBT campaigns on BL Lacertae

Cited by 94 publications

References 26 publications

Multiband optical variability studies of BL Lacertae

Multiband optical variability studies of BL Lacertae

Another look at the BL Lacertae flux and spectral variability

Radio and optical intra-day variability observations of five blazars

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