MULTIWAVELENGTH OBSERVATIONS OF 3C 454.3. I. THE<i>AGILE</i>2007 NOVEMBER CAMPAIGN ON THE “<i>CRAZY DIAMOND</i>”

Vercellone, S.; Chen, A. W.; Vittorini, V.; Giuliani, A.; D’Ammando, F.; Tavani, M.; Donnarumma, I.; Pucella, G.; Raiteri, C. M.; Villata, M.; Chen, W. P.; Tosti, G.; Impiombato, D.; Romano, P.; Belfiore, A.; Luca, A. De; Novara, G.; Senziani, F.; Bazzano, A.; Fiocchi, M.; Ubertini, P.; Ferrari, A.; Argan, A.; Barbiellini, G.; Boffelli, F.; Bulgarelli, A.; Caraveo, P. A.; Cattaneo, P. W.; Cocco, V.; Costa, E.; Monte, E. Del; Paris, G. De; Cocco, G. Di; Evangelista, Y.; Feroci, M.; Fiorini, M.; Fornari, F.; Froysland, T.; Fuschino, F.; Galli, M.; Gianotti, F.; Labanti, C.; Lapshov, I.; Lazzarotto, F.; Lipari, P.; Longo, F.; Marisaldi, M.; Mereghetti, S.; Morselli, A.; Pacciani, L.; Perotti, F.; Picozza, P.; Prest, M.; Rapisarda, M.; Rappoldi, A.; Soffitta, P.; Trifoglio, M.; Trois, A.; Vallazza, E.; Zambra, A.; Zanello, D.; Pittori, C.; Verrecchia, F.; Santolamazza, P.; Preger, B.; Gasparrini, D.; Cutini, S.; Giommi, P.; Colafrancesco, S.; Salotti, L.

doi:10.1088/0004-637x/690/1/1018

Cited by 69 publications

(45 citation statements)

References 51 publications

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“…The data from AGILE and Fermi were separately used to study the correlations between flux variations in optical and γ-rays. All results agreed that the time lag of γ-ray flux variations after the optical 1 http://www.oato.inaf.it/blazars/webt/ 2 http://agile.iasf-roma.inaf.it/ 3 http://fermi.gsfc.nasa.gov/ ones is less than one day (Vercellone et al 2009;Donnarumma et al 2009;Bonning et al 2009;Vercellone et al 2010). Finke & Dermer (2010) discuss the spectral break at ∼2.4 GeV shown by Fermi data in August 2008 suggesting that it results from the combination of Compton-scattered disc and BLR radiations.…”

Section: Introductionsupporting

confidence: 71%

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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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Section: Introductionsupporting

confidence: 71%

“…The results of these observations were published in Vercellone et al (2008), Raiteri et al (2008a,b), Vercellone et al (2009), Donnarumma et al (2009), Villata et al (2009a), and Vercellone et al (2010). Rotations of the optical polarisation vector both clockwise and counterclockwise were detected by Sasada et al (2010).…”

Section: Introductionmentioning

confidence: 74%

The long-lasting activity of 3C 454.3

Raiteri

Villata

Aller

et al. 2011

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“…For instance, an upper limit lag of about 1 day between IR/optical and gamma-ray fluxes has been reported (Bonning et al 2009;Vercellone et al 2010), while a possible delay between the gamma-ray and the optical is constrained to within 12 h (Donnarumma et al 2009;Vercellone et al 2009). …”

Section: Correlated Variabilitymentioning

confidence: 99%

Multi-colour optical variability of the blazar 3C 454.3 in 2007–2010

Zhai

Zheng

Wei

2011

A&A

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Context. We present our optical multiband (B and R) observations of the blazar 3C 454.3, which were acquired over 30 nights from August 2007 to December 2010. Aims. We analyse our data to study the optical emission variability properties of 3C 454.3. Methods. The observations were carried out using both the 1 m EOS Telescope (EST) and the 0.8 m Tsinghua-NAOC Telescope (TNT) simultaneously in most nights at the Xinglong Observatory of National Astronomical Observatories, Chinese Academy of Sciences (NAOC). Both telescopes are equipped with the same type of Princeton Instrument CCD and standard Johnson-Cousin UBVRI filters. To reach a similar signal-to-noise ratio (S/N) in different bands with the same exposure time, observations using the larger diameter EST were carried out with B-band filter, while those of the smaller diameter TNT were carried out with R-band filter. Any time differences between the two telescopes were corrected using GPS. The typical sampling rate was one data point per minute, which is the highest time-resolution so far. Results. A multi-peak outburst was observed during November-December 2007, in addition to a later outburst during October 27-November 1, 2010. The brightest magnitudes for 3C 454.3 during our observations were B = 13.77 mag and R = 12.69 mag at JD = 2 454 436.0952 (December 1, 2007). One of the most striking events was detected on December 1, 2007, when a flux increase of about 0.67 mag occurred in 3.2 h. A colour analysis shows that the colour variability processes are apparently complex. A bluer-when-brighter trend, a redder-when-brighter trend (generally in faint states), and no significant colour variance were all detected during the outburst of November-December 2007. Furthermore, the kind of "saturation" effect in the B − R trend is not visible in the bright state (R < 14) during August 12-14, 2007. These trends may be due to the interactive contribution from the accretion disc and the jet components. Meanwhile, intra-night variability in B and R bands was found to be correlated, without any time delay exceeding one minute.

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“…However, recent multiwavelength studies on a number of blazars, which included observations by the γ-ray satellite AGILE, have shown that multiple SSC and/or EC components are necessary to explain the observed high-energy fluxes (see e.g. Chen et al 2008;Pucella et al 2008;Vercellone et al 2009;D'Ammando et al 2009;Donnarumma et al 2009a).…”

Section: Introductionmentioning

confidence: 99%

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

Raiteri

Villata

Capetti

et al. 2009

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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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MULTIWAVELENGTH OBSERVATIONS OF 3C 454.3. I. THEAGILE2007 NOVEMBER CAMPAIGN ON THE “CRAZY DIAMOND”

Cited by 69 publications

References 51 publications

The long-lasting activity of 3C 454.3

The long-lasting activity of 3C 454.3

Multi-colour optical variability of the blazar 3C 454.3 in 2007–2010

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

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MULTIWAVELENGTH OBSERVATIONS OF 3C 454.3. I. THEAGILE2007 NOVEMBER CAMPAIGN ON THE “CRAZY DIAMOND”

Cited by 69 publications

References 51 publications

The long-lasting activity of 3C 454.3

The long-lasting activity of 3C 454.3

Multi-colour optical variability of the blazar 3C 454.3 in 2007–2010

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

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