-
V. M. 181. Larionov,
S. G. Jorstad,
A. P. Marscher,
C. M. Raiteri,
M. Villata,
I. Agudo,
M. F. Aller,
A. A. Arkharov,
I. M. Asfandiyarov,
U. Bach, [......],
N. Smith,
A. Strigachev,
N. Sumitomo,
L. O. Takalo,
K. Tanaka,
C. Trigilio,
G. Umana,
H. Ungerechts,
A. Volvach,
W. Yuan
Astronomy and Astrophysics 01/2008; 492(2):389. · 4.59 Impact Factor
-
C. M. Raiteri,
M. Villata,
V. M. Larionov,
T. Pursimo, M. A. Ibrahimov,
K. Nilsson,
M. F. Aller,
O. M. Kurtanidze,
L. Foschini,
J. Ohlert, [......],
L. Takalo,
K. Tanaka,
M. Tavani,
M. Tornikoski,
C. Trigilio,
G. Umana,
S. Vercellone,
A. Valcheva,
L. Volvach,
M. Yamanaka
Astronomy and Astrophysics 10/2007; 473(3):819. · 4.59 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The blazar 3C 454.3 underwent an unprecedented optical outburst in spring
2005. This was first followed by a mm and then by a cm radio outburst, which
peaked in February 2006. We report on follow-up observations by the WEBT to
study the multiwavelength emission in the post-outburst phase. XMM-Newton
observations on July and December 2006 added information on the X-ray and UV
fluxes. The source was in a faint state. The radio flux at the higher
frequencies showed a fast decreasing trend, which represents the tail of the
big radio outburst. It was followed by a quiescent state, common at all radio
frequencies. In contrast, moderate activity characterized the NIR and optical
light curves, with a progressive increase of the variability amplitude with
increasing wavelength. We ascribe this redder-when-brighter behaviour to the
presence of a "little blue bump" due to line emission from the broad line
region, which is clearly visible in the source SED during faint states.
Moreover, the data from the XMM-Newton OM reveal a rise of the SED in the UV,
suggesting the existence of a "big blue bump" due to thermal emission from the
accretion disc. The X-ray spectra are well fitted with a power-law model with
photoelectric absorption, possibly larger than the Galactic one. However, the
comparison with previous X-ray observations would imply that the amount of
absorbing matter is variable. Alternatively, the intrinsic X-ray spectrum
presents a curvature, which may depend on the X-ray brightness. In this case,
two scenarios are possible.
08/2007;
-
M. 126. Villata,
C. M. Raiteri,
M. F. Aller,
U. Bach, M. A. Ibrahimov,
Y. Y. Kovalev,
O. M. Kurtanidze,
V. M. Larionov,
C.-U. Lee,
P. Leto, [......],
K. Sadakane,
S. G. Sergeev,
L. A. Sigua,
A. Sillanpää,
R. L. Smart,
L. O. Takalo,
K. Tanaka,
M. Tornikoski,
C. Trigilio,
G. Umana
Astronomy and Astrophysics 03/2007; 464(2):5. · 4.59 Impact Factor
-
S. Ciprini,
C.M. Raiteri,
N. Rizzi,
I. Agudo,
L. Foschini,
M. Fiorucci,
L.O. Takalo,
M. Villata,
L. Ostorero,
A. Sillanpaa, [......],
I. Torniainen,
M. Tornikoski,
G. Umana,
H. Ungerechts,
E. Valtaoja,
A. Volvach,
J.R. Webb,
J. Wu,
H.-S. Yim,
Y. Zhang
Bollettino della Societa Paleontologica Italiana 01/2007; 78:741. · 0.49 Impact Factor
-
U. Bach,
C. M. Raiteri,
M. Villata,
L. Fuhrmann,
C. S. Buemi,
V. M. Larionov,
P. Leto,
A. A. Arkharov,
J. M. Coloma,
A. Di Paola, [......],
E. Kopatskaya,
L. Lanteri,
O. M. Kurtanidze,
G. Maccaferri,
M. G. Nikolashvili,
A. Orlati,
J. A. Ros,
G. Tosti,
C. Trigilio,
G. Umana
[show abstract]
[hide abstract]
ABSTRACT: Context: Being dominated by non-thermal emission from aligned relativistic jets, blazars allow us to elucidate the physics of extragalactic jets, and, ltimately, how the energy is extracted from the central black hole in radio-loud active galactic nuclei. Aims: Crucial information is provided by broad-band spectral energy distributions (SEDs), their trends with luminosity and correlated multi-frequency variability. With this study we plan to obtain a database of contemporaneous radio-to-optical spectra of a sample of blazars, which are and will be observed by current and future high-energy satellites. Methods: Since December 2004 we are performing a monthly multi-frequency radio monitoring of a sample of 35 blazars at the antennas in Medicina and Noto. Contemporaneous near-IR and optical observations for all our observing epochs are organised. Results: Until June 2006 about 4000 radio measurements and 5500 near-IR and optical measurements were obtained. Most of the sources show significant variability in all observing bands. Here we present the multi-frequency data acquired during the first eighteen months of the project, and construct the SEDs for the best-sampled sources. Comment: 16 pages, 3 large figures, accepted for publication in A&A
12/2006;
-
[show abstract]
[hide abstract]
ABSTRACT: A huge multiwavelength campaign targeting the blazar AO 0235+164 was organized by the Whole Earth Blazar Telescope (WEBT) in 2003-2005 to study the variability properties of the source. Monitoring observations were carried out at cm and mm wavelengths, and in the near-IR and optical bands, while three pointings by the XMM-Newton satellite provided information on the X-ray and UV emission. We present the data acquired during the second observing season, 2004-2005, by 27 radio-to-optical telescopes. They reveal an increased near-IR and optical activity with respect to the previous season. Increased variability is also found at the higher radio frequencies, down to 15 GHz, but not at the lower ones. The radio (and optical) outburst predicted to peak around February-March 2004 on the basis of the previously observed 5-6 yr quasi-periodicity did not occur. The analysis of the optical light curves reveals now a longer characteristic time scale of 8 yr, which is also present in the radio data. The spectral energy distributions corresponding to the XMM-Newton observations performed during the WEBT campaign are compared with those pertaining to previous pointings of X-ray satellites. Bright, soft X-ray spectra can be described in terms of an extra component, which appears also when the source is faint through a hard UV spectrum and a curvature of the X-ray spectrum. Finally, there might be a correlation between the X-ray and optical bright states with a long time delay of about 5 yr, which would require a geometrical interpretation. Comment: 14 pages, 10 figures (8 included in the text and 2 PNG files), in press for A&A
08/2006;
-
[show abstract]
[hide abstract]
ABSTRACT: A multiwavelength campaign on the BL Lac object AO 0235+16 has been organized by the WEBT collaboration during the observing seasons 2003-2004 and 2004-2005. Here we report on the results of the first season, which saw the participation of 24 optical and near-IR telescopes and 4 radio telescopes, as well as the first XMM-Newton pointing, which occurred on January 18-19, 2004. Unpublished data from previous epochs were also collected. In the optical and near-IR the source has been very active in the last 3 years, though rather faint most of the time, with noticeable variations of more than a mag in a few days. In contrast, in the radio bands it appears "quiescent" since early 2000. The X-ray spectra obtained by the three EPIC detectors are well fitted by a power law with extra-absorption at z=0.524. No significant variation of the X-ray flux occurred during the pointing. In contrast, contemporaneous dense radio monitoring with the 100 m telescope at Effelsberg shows a ~2-3% flux decrease in 6-7 hours, which, if intrinsic, would imply a brightness temperature well above the Compton limit. We construct the broad-band spectral energy distribution of January 18-19, 2004 with simultaneous radio data from Effelsberg, optical data from the Nordic Optical Telescope, optical-UV data from the Optical Monitor onboard XMM-Newton, and X-ray data by the EPIC instruments. Particular care was taken to correct data for extinction due to both the Milky Way and the z=0.524 absorber. The resulting SED suggests the existence of a bump in the UV spectral region. Comment: 15 pages, 12 figures (7 included, 5 separate PNG files), in press for Astronomy and Astrophysics
03/2005;
-
C. M. Raiteri,
M. Villata,
L. Lanteri,
L. Ostorero,
G. Tosti,
S. Ciprini,
G. Nucciarelli,
R. Nesci,
E. Massaro,
M. Maesano,
F. Montagni,
I. E. Papadakis,
O. M. Kurtanidze,
M. G. Nikolashvili, M. A. Ibrahimov,
M. F. Aller,
H. D. Aller,
H. Teräsranta
[show abstract]
[hide abstract]
ABSTRACT: The radio and optical behaviour of the BL Lacertae object 0716+714 from
1994 to 2001 has been investigated by a wide international collaboration
including eight optical telescopes in Italy, Greece, Georgia (FSU), and
Uzbekistan and two radio antennas in USA and in Finland. The optical
light curves show a long-term trend on which fast variations are
superposed. The mean brightness level seems to vary with a typical time
scale of about 3.3 years. No clear evidence of correlation between
variations in the optical and radio bands has been found.
06/2003; 299:225.
-
M. Villata,
C. M. Raiteri,
O. M. Kurtanidze,
M. G. Nikolashvili, M. A. Ibrahimov,
I. E. Papadakis,
K. Tsinganos,
K. Sadakane,
N. Okada,
L. O. Takalo, [......],
E. G. Larionova,
K. Matsumoto,
J. R. Mattox,
F. Montagni,
G. Nucciarelli,
L. Ostorero,
J. Papamastorakis,
M. Pasanen,
G. Sobrito,
M. Uemura
[show abstract]
[hide abstract]
ABSTRACT: The Whole Earth Blazar Telescope (WEBT) is an international consortium
of about 30 optical observatories and 2 radio observatories devoted to
blazar monitoring during optical and multifrequency campaigns. The
dispersion in longitude of the WEBT members allows them to obtain dense
and quasi-continuous light curves, minimizing gaps due to Earth
rotation. A few results from the BL Lac 2000 WEBT campaign are briefly
presented here.
06/2003; 299:221.
-
C. M. Raiteri,
M. Villata,
G. Tosti,
R. Nesci,
E. Massaro,
M. F. Aller,
H. D. Aller,
H. Terasranta,
O. M. Kurtanidze,
M. G. Nikolashvili, [......],
U. Bach,
G. Cimo,
S. Ciprini,
L. Fuhrmann,
G. N. Kimeridze,
L. Lanteri,
M. Maesano,
F. Montagni,
G. Nucciarelli,
L. Ostorero
[show abstract]
[hide abstract]
ABSTRACT: Eight optical and four radio observatories have been intensively monitoring
the BL Lac object 0716+714 in the last years: 4854 data points have been
collected in the UBVRI bands since 1994, while radio light curves extend back
to 1978. Many of these data are presented here for the first time. The
long-term trend shown by the optical light curves seems to vary with a
characteristic time scale of about 3.3 years, while a longer period of 5.5-6
years seems to characterize the radio long-term variations. In general, optical
colour indices are only weakly correlated with brightness. The radio flux
behaviour at different frequencies is similar, but the flux variation amplitude
decreases with increasing wavelength. The radio spectral index varies with
brightness (harder when brighter), but the radio fluxes seem to be the sum of
two different-spectrum contributions: a steady base level and a harder-spectrum
variable component. Once the base level is removed, the radio variations appear
as essentially achromatic, similarly to the optical behaviour. Flux variations
at the higher radio frequencies lead the lower-frequency ones with week-month
time scales. The behaviour of the optical and radio light curves is quite
different, the broad radio outbursts not corresponding in time to the faster
optical ones and the cross-correlation analysis indicating only weak
correlation with long time lags. However, minor radio flux enhancements
simultaneous with the major optical flares can be recognized, which may imply
that the mechanism producing the strong flux increases in the optical band also
marginally affects the radio one.
02/2003;
-
[show abstract]
[hide abstract]
ABSTRACT: We present the most continuous data base of optical $BVR_{c}I_{c}$ observations ever published on the BL Lacertae object GC 0109+224, collected mainly by the robotic telescope of the Perugia University Observatory in the period November 1994-February 2002. These observations have been complemented by data from the Torino Observatory, collected in the period July 1995-January 1999, and Mt. Maidanak Observatory (December 2000). GC 0109+224 showed rapid optical variations and six major outbursts were observed at the beginning and end of 1996, in fall 1998, at the beginning and at the end of 2000, and at the beginning of 2002. Fast and large-amplitude drops characterized its flux behaviour. The $R_c$ magnitude ranged from 13.3 (16.16 mJy) to 16.46 (0.8 mJy), with a mean value of 14.9 (3.38 mJy). In the periods where we collected multi-filter observations, we analyzed colour and spectral indexes, and the variability patterns during some flares. The long-term behaviour seems approximatively achromatic, but during some isolated outbursts we found evidence of the typical loop-like hysteresis behaviour, suggesting that rapid optical variability is dominated by non-thermal cooling of a single emitting particle population. We performed also a statistical analysis of the data, through the discrete correlation function (DCF), the structure function (SF), and the Lomb-Scargle periodogram, to identify characteristic times scales, from days to months, in the light curves, and to quantify the mode of variability. We also include the reconstruction of the historical light curve and a photometric calibration of comparison stars, to favour further extensive optical monitoring of this interesting blazar.
02/2003;
-
M. Villata,
C. M. Raiteri,
O. M. Kurtanidze,
M. G. Nikolashvili, M. A. Ibrahimov,
I. E. Papadakis,
K. Tsinganos,
K. Sadakane,
N. Okada,
L. O. Takalo, [......],
E. G. Larionova,
K. Matsumoto,
J. R. Mattox,
F. Montagni,
G. Nucciarelli,
L. Ostorero,
J. Papamastorakis,
M. Pasanen,
G. Sobrito,
M. Uemura
10/2002; -1:152.
-
S. Ciprini,
C. M. Raiteri,
N. Rizzi,
I. Agudo,
L. Foschini,
M. Fiorucci,
L. O. Takalo,
M. Villata,
L. Ostorero,
A. Sillanpää, [......],
Torniainenk I,
M. Tornikoski,
G. Umana,
H. Ungerechts,
E. Valtaoja,
A. Volvach,
J. R. Webb,
J. Wu,
H.-S. Yim,
Y. Zhang
[show abstract]
[hide abstract]
ABSTRACT: Two guest-observer XMM-Newton pointings of the blazar OJ 287 in 2005 are
introduced, along with part of the radio, mm, near-IR, and optical data
obtained during a coordinated and intensive WEBT campaign, during
longer-term monitoring observations performed by teams of the ENIGMA
network, and during other independent observing programs (like VLBA
observations). In that year OJ 287 showed an interesting variable
behavior in the optical band. An optical outburst, well matched by our
WEBT observations, is claimed in the period Oct.-Nov. 2005, and the
XMM-Newton X-ray observations are performed in correspondence with two
active optical states (an intermediate flare and such outburst). X-ray
data indicates different flux levels, spectral slopes, and emission
components, and VLBA radio maps are consistent with a jet precession
model. This appreciable observing effort is still ongoing (a further
XMM-Newton pointing is planned in 2008), joined with further
parallel/multi-monitoring observing programmes devoted to this
interesting object.
Memorie della Societa Astronomica Italiana. 78:741.
-
M. Böttcher,
A. P. Marscher,
M. Ravasio,
M. Villata,
C. M. Raiteri,
H. D. Aller,
M. F. Aller,
H. Teräsranta,
O. Mang,
G. Tagliaferri, [......],
K Matsumoto,
J. R. Mattox,
I. McHardy,
F. Montagni,
G. Nucciarelli,
L. Ostorero,
J. Papamastorakis,
M. Pasanen,
G. Sobrito,
M Uemura
[show abstract]
[hide abstract]
ABSTRACT: BL Lacertae (BL Lac) was the target of an extensive multiwavelength monitoring campaign in the second half of 2000. Simultaneous or quasi-simultaneous observations were taken at radio (University of Michigan Radio Astronomy Observatory and Metsähovi Radio Telescope) and optical (Whole Earth Blazar Telescope [WEBT] collaboration) frequencies, in X-rays (BeppoSAX and RXTE), and at very high energy gamma rays (HEGRA). The WEBT optical campaign achieved an unprecedented time coverage, virtually continuous over several 10–20 hr segments. It revealed intraday variability on timescales of ∼1.5 hr and evidence for spectral hardening associated with increasing optical flux. During the campaign, BL Lac underwent a major transition from a rather quiescent state prior to 2000 September, to a flaring state for the rest of the year. This was also evident in the X-ray activity of the source. BeppoSAX observations on July 26–27 revealed a rather low X-ray flux and a hard spectrum, while a BeppoSAX pointing on 2000 October 31–November 2 indicated significant variability on timescales of ≲a few hours and provided evidence for the synchrotron spectrum extending out to ∼10 keV during that time. During the July 26–27 observation, there is a tantalizing, although not statistically significant, indication of a time delay of ∼4–5 hr between the BeppoSAX and the R-band light curves. Also, a low-significance detection of a time delay of 15 days between the 14.5 and 22 GHz radio light curves is reported. Several independent methods to estimate the comoving magnetic field in the source are presented, suggesting a value of ∼2e G, where eB is the magnetic field equipartition factor with respect to the electron energy density in the jet.
Astrophysical Journal, v.596, 847-859 (2003).
-
M. Villata,
C. M. Raiteri,
O. M. Kurtanidze,
M. G. Nikolashvili, M. A. Ibrahimov,
I. E. Papadakis,
G. Tosti,
F. Hroch,
L. O. Takalo,
A. Sillanpää, [......],
J. Papamastorakis,
M. Pasanen,
C. S. Peters,
T. Pursimo,
P. Reig,
W. Ryle,
S. Sclavi,
L. A. Sigua,
M Uemura,
W. Wills
[show abstract]
[hide abstract]
ABSTRACT: BL Lacertae has been the target of four observing campaigns by the Whole Earth Blazar Telescope (WEBT) collaboration. In this paper we present ${\it UBVRI}$ light curves obtained by the WEBT from 1994 to 2002, including the last, extended BL Lac 2001 campaign. A total of about 7500 optical observations performed by 31 telescopes from Japan to Mexico have been collected, to be added to the ~$15\,600$ observations of the BL Lac Campaign 2000. All these data allow one to follow the source optical emission behaviour with unprecedented detail. The analysis of the colour indices reveals that the flux variability can be interpreted in terms of two components: longer-term variations occurring on a few-day time scale appear as mildly-chromatic events, while a strong bluer-when-brighter chromatism characterizes very fast (intraday) flares. By decoupling the two components, we quantify the degree of chromatism inferring that longer-term flux changes imply moving along a ~$ 0.1$ bluer-when-brighter slope in the $B-R$ versus $R$ plane; a steeper slope of ~$ 0.4$ would distinguish the shorter-term variations. This means that, when considering the long-term trend, the $B$-band flux level is related to the $R$-band one according to a power law of index ~$ 1.1$. Doppler factor variations on a “convex" spectrum could be the mechanism accounting for both the long-term variations and their slight chromatism.
http://dx.doi.org/10.1051/0004-6361:20035895.
-
M. Villata,
C. M. Raiteri,
H. D. Aller,
M. F. Aller,
H. Teräsranta,
P. Koivula,
S. Wiren,
O. M. Kurtanidze,
M. G. Nikolashvili, M. A. Ibrahimov, [......],
G. Tosti,
F. Hroch,
L. O. Takalo,
A. Sillanpää,
V. A. Hagen-Thorn,
V. M. Larionov,
R. D. Schwartz,
J. Basler,
L. F. Brown,
T. J. Balonek
[show abstract]
[hide abstract]
ABSTRACT: The Whole Earth Blazar Telescope (WEBT) collaboration has collected a large amount of optical and radio data on BL Lacertae in the last years, which, when added to literature data, allow to construct well-sampled light curves of the source from 1968 to the end of 2003. These optical and radio data are here analysed with three statistical methods designed for unevenly-sampled data trains in order to search for possible periodicities. While the main radio outbursts repeat every ~$8$ years, with a possible progressive stretching of the period, the evidence of an optical periodicity is much less clear. Radio light curves from 4.8 to 37 GHz are well correlated, with variations at the higher frequencies leading the lower-frequency ones by a few weeks for contiguous bands, up to a few months when considering the largest frequency separations. The radio behaviour reveals the presence of two different components, the softer-spectrum one constituting the bulk of the radio emission. On the other hand, the harder component shows itself as radio events which appear enhanced at the higher frequencies and seem to have optical counterparts. Cross-correlation between the optical light curve and radio hardness ratios indicates a radio time delay of more than 3 months. Thus, our analysis suggests a scenario where flux variations propagate towards less and less opaque regions, giving rise to related optical and hard radio events and, in more extended zones, to soft events apparently uncorrelated with the former ones.
http://dx.doi.org/10.1051/0004-6361:20040439.
-
[show abstract]
[hide abstract]
ABSTRACT: We present the most continuous data base of optical $BVR_{\rm c}I_{\rm c}$ observations ever published on the BL Lacertae object GC 0109+224, collected mainly by the robotic telescope of the Perugia University Observatory in the period November 1994-February 2002. These observations have been complemented by data from the Torino Observatory, collected in the period July 1995-January 1999, and Mt. Maidanak Observatory (December 2000). GC 0109+224 showed rapid optical variations and six major outbursts were observed at the beginning and end of 1996, in fall 1998, at the beginning and at the end of 2000, and at the beginning of 2002. Fast and large-amplitude drops characterized its flux behaviour. The $R_{\rm c}$ magnitude ranged from 13.3 (16.16 mJy) to 16.46 (0.8 mJy), with a mean value of 14.9 (3.38 mJy). In the periods where we collected multi-filter observations, we analyzed colour and spectral indexes, and the variability patterns during some flares. The long-term behaviour seems approximatively achromatic, but during some isolated outbursts we found evidence of the typical loop-like hysteresis behaviour, suggesting that rapid optical variability is dominated by non-thermal cooling of a single emitting particle population. We performed also a statistical analysis of the data, through the discrete correlation function (DCF), the structure function (SF), and the Lomb-Scargle periodogram, to identify characteristic times scales, from days to months, in the light curves, and to quantify the mode of variability. We also include the reconstruction of the historical light curve and a photometric calibration of comparison stars, to favour further extensive optical monitoring of this interesting blazar.
http://dx.doi.org/10.1051/0004-6361:20030045.
-
M. Villata,
C. M. Raiteri,
O. M. Kurtanidze,
M. G. Nikolashvili, M. A. Ibrahimov,
I. E. Papadakis,
G. Tosti,
F. Hroch,
L. O. Takalo,
A. Sillanpää, [......],
J. Papamastorakis,
M. Pasanen,
C. S. Peters,
T. Pursimo,
Pablo Reig Torres,
W. Ryle,
S. Sclavi,
L. A. Sigua,
M Uemura,
W. Wills
[show abstract]
[hide abstract]
ABSTRACT: BL Lacertae has been the target of four observing campaigns by the Whole Earth Blazar Telescope (WEBT) collaboration. In this paper we present UBVRI light curves obtained by theWEBT from 1994 to 2002, including the last, extended BL Lac 2001 campaign. A total of about 7500 optical observations performed by 31 telescopes from Japan to Mexico have been collected, to be added to the ∼15 600 observations of the BL Lac Campaign 2000. All these data allow one to follow the source optical emission behaviour with unprecedented detail. The analysis of the colour indices reveals that the flux variability can be interpreted in terms of two components: longer-term variations occurring on a fewday time scale appear as mildly-chromatic events, while a strong bluer-when-brighter chromatism characterizes very fast (intraday) flares. By decoupling the two components, we quantify the degree of chromatism inferring that longer-term flux changes imply moving along a ∼0.1 bluerwhen- brighter slope in the B − R versus R plane; a steeper slope of ∼0.4 would distinguish the shorter-term variations. This means that, when considering the long-term trend, the B-band flux level is related to the R-band one according to a power law of index ∼1.1. Doppler factor variations on a “convex” spectrum could be the mechanism accounting for both the long-term variations and their slight chromatism. Reig Torres, Pablo, Pablo.Reig@uv.es
VILLATA, M. et al. 2004, The WEBT BL Lacertae Campaign 2001 and its extension : Optical light curves and colour analysis 1994–2002, Astronomy and Astrophysics, vol. 421, no. 1, p. 103-114.
-
U. Bach,
C. M. Raiteri,
M. Villata,
L. Fuhrmann,
C. S. Buemi,
V. M. Larionov,
P. Leto,
A. A. Arkharov,
J. M. Coloma,
A. Di Paola, [......],
E. Kopatskaya,
L. Lanteri,
O. M. Kurtanidze,
G. Maccaferri,
M. G. Nikolashvili,
A. Orlati,
J. A. Ros,
G. Tosti,
C. Trigilio,
G. Umana
[show abstract]
[hide abstract]
ABSTRACT: Context.Being dominated by non-thermal emission from aligned relativistic jets, blazars allow us to elucidate the physics of extragalactic jets, and, ultimately, how the energy is extracted from the central black hole in radio-loud active galactic nuclei.Aims.Crucial information is provided by broad-band spectral energy distributions (SEDs), their trends with luminosity and correlated multi-frequency variability. With this study we plan to obtain a database of contemporaneous radio-to-optical spectra of a sample of blazars, which are and will be observed by current and future high-energy satellites.Methods.Since December 2004 we are performing a monthly multi-frequency radio monitoring of a sample of 35 blazars at the antennas in Medicina and Noto. Contemporaneous near-IR and optical observations for all our observing epochs are organised.Results.Until June 2006 about 4000 radio measurements and 5500 near-IR and optical measurements were obtained. Most of the sources show significant variability in all observing bands. Here we present the multi-frequency data acquired during the first eighteen months of the project, and construct the SEDs for the best-sampled sources.
http://dx.doi.org/10.1051/0004-6361:20066561.
