Coordinated Multiwavelength Observations of BL Lacertae in 2000

Böttcher, M.; Marscher, A. P.; Ravasio, M.; Villata, M.; Raiteri, C. M.; Aller, H. D.; Aller, M. F.; Teräsranta, H.; Mang, O.; Tagliaferri, G.; Aharonian, F.; Krawczynski, H.; Kurtanidze, O. M.; Nikolashvili, M. G.; Ibrahimov, M.; Papadakis, I. E.; Tsinganos, K.; Sadakane, Kozo; Okada, Norio; Takalo, L. O.; Sillanpää, A.; Tosti, G.; Ciprini, S.; Frasca, A.; Marilli, E.; Robb, R. M.; Noble, J. C.; Jorstad, S. G.; Hagen-Thorn, V. A.; Ларионов, В. М.; Nesci, R.; Maesano, M.; Schwartz, Richard D.; Basler, Joseph W.; Gorham, P. W.; Iwamatsu, H.; Katô, Takeo; Pullen, C.; Benítez, E.; Diego, J. A. de; Moilanen, Marko; Oksanen, A.; Rodríguez, D.; Sadun, A. C.; Kelly, M.; Carini, M. T.; Miller, H. R.; Catalano, S.; Dultzin‐Hacyan, D.; Jiang, Fan; Ghisellini, G.; Ishioka, Ryoko; Karttunen, Hannu; Keinänen, P.; Kudryavtseva, N. A.; Lainela, M.; Lanteri, L.; Ларионова, Е. Г.; Matsumoto, Katsura; Mattox, J. R.; McHardy, I. M.; Montagni, F.; Nucciarelli, G.; Ostorero, L.; Papamastorakis, I.; Pasanen, M.; Sobrito, G.; Uemura, Makoto

doi:10.1086/378156

Cited by 74 publications

(72 citation statements)

References 48 publications

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“…In contrast, in November 2000 the whole X-ray spectrum was steep, and its extrapolation to optical frequencies was not intersecting the simultaneous optical spectrum. This offset was questioned by Böttcher et al (2003), who warned about the possibility that it was produced by flux averaging in a period of noticeable variability, as shown by the intensive monitoring performed by the WEBT observers during the 2000-2001 observing season (Villata et al 2002). However, to remove the offset we should have missed one or more big flares, such as to increase the mean optical level by more than 1 mag, which seems unlikely.…”

Section: Comparison With Previous Observationsmentioning

confidence: 99%

“…In the last decade, BL Lacertae has been extensively studied by the Whole Earth Blazar Telescope (WEBT) collaboration 1 , which has carried out several multiwavelength campaigns on this object (Villata et al 2002;Ravasio et al 2002;Böttcher et al 2003;Villata et al 2004a,b;Bach et al 2006;Papadakis et al 2007;Villata et al 2009), collecting tens of thousands of opticalto-radio data. These studies were focused on its multiwavelength flux variability, colour behaviour, correlations among flux variations in different bands, possible periodicity of the radio outbursts.…”

Section: Introductionmentioning

confidence: 99%

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WEBT multiwavelength monitoring and XMM-Newton observations of  BL Lacertae in 2007–2008

Raiteri

Villata

Capetti

et al. 2009

A&A

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Context. BL Lacertae is the prototype of the blazar subclass named after it. Yet, it has occasionally shown a peculiar behaviour that has questioned a simple interpretation of its broad-band emission in terms of synchrotron plus synchrotron self-Compton (SSC) radiation. Aims. In the 2007-2008 observing season we carried out a new multiwavelength campaign of the Whole Earth Blazar Telescope (WEBT) on BL Lacertae, involving three pointings by the XMM-Newton satellite in July and December 2007, and January 2008, to study its emission properties, particularly in the optical-X-ray energy range. Methods. The source was monitored in the optical-to-radio bands by 37 telescopes. The brightness level was relatively low. Some episodes of very fast variability were detected in the optical bands. Flux changes had larger amplitude at the higher radio frequencies than at longer wavelengths. Results. The X-ray spectra acquired by the EPIC instrument onboard XMM-Newton are well fitted by a power law with photon index Γ ∼ 2 and photoelectric absorption exceeding the Galactic value. However, when taking into account the presence of a molecular cloud on the line of sight, the EPIC data are best fitted by a double power law, implying a concave X-ray spectrum. The spectral energy distributions (SEDs) built with simultaneous radio-to-X-ray data at the epochs of the XMM-Newton observations suggest that the peak of the synchrotron emission lies in the near-IR band, and show a prominent UV excess, besides a slight soft-X-ray excess. A comparison with the SEDs corresponding to previous observations with X-ray satellites shows that the X-ray spectrum is very variable, since it can change from extremely steep to extremely hard, and can be more or less curved in intermediate states. We ascribe the UV excess to thermal emission from the accretion disc, and the other broad-band spectral features to the presence of two synchrotron components, with their related SSC emission. We fit the thermal emission with a black body law and the non-thermal components by means of a helical jet model. The fit indicates a disc temperature > ∼ 20 000 K and a luminosity > ∼ 6 × 10 44 erg s −1 .

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Section: Comparison With Previous Observationsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

WEBT multiwavelength monitoring and XMM-Newton observations of  BL Lacertae in 2007–2008

Raiteri

Villata

Capetti

et al. 2009

A&A

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“…Collaboration et al 2011). Due to its pronounced variability over entire electromagnetic spectra it has been continuously monitored with Whole Earth Blazar Telescope (WEBT) 1 since 1997 till today; which involves four major WEBT multi-frequency campaigns, two of them were organized in 1999 supplemented with ASCA and Beppo SAX observations (Ravasio et al 2002) (Villata et al 2002;Böttcher et al 2003;Villata et al 2004a,b). Carini et al (1992) studied two optically bright sources, OJ 287 and BL Lacertae using a decade long photometric observations where they found IDV of the order of 0.08 mag/hr in former and 0.01 mag/hr for later.…”

Section: Introductionmentioning

confidence: 99%

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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“…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

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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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Coordinated Multiwavelength Observations of BL Lacertae in 2000

Cited by 74 publications

References 48 publications

WEBT multiwavelength monitoring and XMM-Newton observations of  BL Lacertae in 2007–2008

WEBT multiwavelength monitoring and XMM-Newton observations of  BL Lacertae in 2007–2008

Multiband optical variability studies of BL Lacertae

Another look at the BL Lacertae flux and spectral variability

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Coordinated Multiwavelength Observations of BL Lacertae in 2000

Cited by 74 publications

References 48 publications

WEBT multiwavelength monitoring and XMM-Newton observations of BL Lacertae in 2007–2008

WEBT multiwavelength monitoring and XMM-Newton observations of BL Lacertae in 2007–2008

Multiband optical variability studies of BL Lacertae

Another look at the BL Lacertae flux and spectral variability

Contact Info

Product

Resources

About

WEBT multiwavelength monitoring and XMM-Newton observations of  BL Lacertae in 2007–2008

WEBT multiwavelength monitoring and XMM-Newton observations of  BL Lacertae in 2007–2008