Radio monitoring of a sample of X-and $\vec{\gamma}$-ray loud blazars

Venturi, T.; Dallacasa, D.; Orfei, A.; Bondì, M.; Fanti, R.; Gregorini, L.; Mantovani, F.; Stanghellini, C.; Trigilio, C.; Umana, G.

doi:10.1051/0004-6361:20011232

Cited by 31 publications

(41 citation statements)

References 16 publications

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“…We compared the light curves of Venturi et al (2001) and Teräsranta et al (2005) with the outflow rate plots of our simulations to find a possible correspondence. The light curves of Teräsranta et al (2005) are at higher frequency and span for 24 years, being more sensitive to the flux variability of the sources.…”

Section: Resultsmentioning

confidence: 99%

“…In low resolution images, the modulation of the gas ejection appears in a radio flux density variability, which is observed in many objects. In particular there are several studies of radio light curves of single objects (e.g., Vicente et al 1996;Raiteri et al 2001) or of group of blazars (e.g., Venturi et al 2001). In latter works, it is possible to recognize a quasi-periodical variability of the sources, much more evident in the high-frequency light curves Teräsranta et al (2005).…”

Section: This Workmentioning

confidence: 99%

“…The production of such blobs is connected with flares in the strongly variable light curves (Perlman et al 2001). Generally, the radio light curves of AGN do not exhibit any periodicity, but the analysis of most time-extended radio light curves of some X and γ ray-loud blazars (Raiteri et al 2001;Venturi et al 2001) shows the signature of a longterm quasi-periodic behaviour. Some of the observed periodic variabilities may be explained by the helical-jet model (Königl & Choudhuri 1985;Camenzind & Krockenberg 1992;Raiteri et al 1999;Guerra 2004;Rieger 2004), but kinematic studies of parsec-scale radio jets have provided observational evidence for helical trajectories only in a few AGN showing periodicities (Vicente et al 1996;Tateyama et al 1998;Gomez et al 1999;Kellermann et al 2004).…”

Section: Introductionmentioning

confidence: 99%

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The role of viscosity in AGN outflows in relation to jet periodicities

Lanzafame¹,

Cassaro

Schillirò

et al. 2008

A&A

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Aims. Adopting the Smoothed Particle Hydrodynamics (SPH) numerical method, we performed a grid of evolving models of a 3D axially-symmetric, viscous accretion disc around a supermassive black hole (SMBH) of 10 6 ÷ 10 9 M . Such sort of simulations are typical of accretion discs in active galactic nuclei (AGN). In such disc models, we pay attention to the role of the specific angular momentum λ and the turbulent viscosity parameter α, according to the Shakura and Sunyaev prescription. One or two shock fronts in the radial inviscid flow develop, according to the assigned initial kinematic and thermodynamic conditions. Methods. By fixing the initial and boundary conditions on the flow at the disc outer edge, where the total energy, the specific angular momentum λ, and the initial velocity are concerned, we find pairs of (α, λ) values determining radial periodical oscillations in the shock front. In some cases, an outflow develops from the subsonic post-shock region, close to the black hole. Results. The link between the accretion disc and the jet refueling through the onset of a centrifugal shock front is evident. We also compare model variability periods with observed ones in the radio light curves of AGN.

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Section: Resultsmentioning

confidence: 99%

Section: This Workmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The role of viscosity in AGN outflows in relation to jet periodicities

Lanzafame¹,

Cassaro

Schillirò

et al. 2008

A&A

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“…A rather faint phase, in which the source was only occasionally brighter than R = 15 but generally fainter than 15.5, lasted about three years from the beginning of 1997 to the end of (Teräsranta et al 1998) and those from 1996 to 1997 (asterisks) from (Venturi et al 2001);data at 8.4 GHz (1996data at 8.4 GHz ( −2000 are also from (Venturi et al 2001) and those at 353 GHz (open circles) are from (Robson et al 2001). Lower panel: time history of the core (filled squares) and the jet (open squares) flux density at 5 GHz of OQ 530 derived from literature and from our observations.…”

Section: Optical Observationsmentioning

confidence: 99%

VLBI imaging and optical variability of the BL Lac object OQ 530 (B1418+546)

Massaro

Mantovani

Fanti

et al. 2004

A&A

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Abstract.Results of VLBI and optical observations are presented for the BL Lac object OQ 530 (B1418+546), whose long term optical variability is characterised by a decreasing mean luminosity trend. EVN images at 1.6 GHz and 5 GHz of OQ 530 show a very bright core with a much weaker jet extending to about 35-40 mas. The radio flux density from the core in June 2001 was much higher than that measured in February 1999. A similar increase was also found from nearly simultaneous optical photometry, while the total flux density of the jet remained unchanged. The structure of the jet shows several knots which move outward with an apparent superluminal motion with a β app ≥ 3.5h −1 . The region within about 3 mas from the core contains a component not well resolved in our images and emerging from it in the jet direction. That component was also detected in images taken from 1990 to 1997 and it seems to be a rather stable structural feature. Using nearly simultaneous optical and radio data, we can describe the SED of the synchrotron peak with a simple formula, approximating a power law at low frequencies and a log-parabola at the high ones, whose maximum lies in the range 3.5−5 × 10 13 Hz, and the extrapolation in the X-ray range gives a flux comparable to that observed with BeppoSAX.

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“…For many decades, Mrk 421 has been a target of regular monitoring at radio frequencies, showing only moderate variability (Aller et al 1999;Venturi et al 2001;Fan et al 2007;Nieppola et al 2009). Multi-wavelength campaigns have failed to reveal significant correlations between variability at high (or very high) energy and radio wavelengths (Abdo et al 2011;Acciari et al 2011).…”

Section: Discussionmentioning

confidence: 99%

Very Long Baseline Polarimetry and the Gamma-ray connection in Markarian 421 during the broadband campaign in 2011

Lico¹,

Giroletti²,

Orienti³

et al. 2015

Proceedings of 12th European VLBI Network Symposium and Users Meeting — PoS(EVN 2014)

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Context. This is the third paper in a series devoted to the analysis of the multiwavelength data from a campaign on the nearby (z = 0.03) TeV blazar Mrk 421 during 2011. Aims. We here investigate the structure of the high angular resolution polarization, the magnetic topology, the total intensity light curve, the γ-ray flux, and the photon index. We describe how they evolve and how they are connected. Methods. We analyzed data in polarized intensity obtained with the Very Long Baseline Array (VLBA) at twelve epochs (one observation per month from January to December 2011) at 15, 24, and 43 GHz. For the absolute orientation of the electric vector position angles (EVPA) we used the D-terms method; we also confirm its accuracy. We also used γ-ray data from the Fermi Large Area Telescope on weekly time bins throughout 2011. Results. The source shows polarized emission, and its properties vary with time, frequency, and location along the jet. The core mean polarization fraction is generally between 1% and 2%, with a 4% peak at 43 GHz in March; the polarization angle is variable, mainly at 15 GHz, where it changes frequently, and less so at 43 GHz, where it oscillates in the range 114• − 173• . The jet polarization properties are more stable, with a fractional polarization of around 16% and a polarization angle nearly perpendicular to the jet axis. The average flux and photon index at γ-ray energies are (17.4 ± 0.5) ×10 −8 ph cm −2 s −1 and Γ = 1.77 ± 0.02. The γ-ray light curve shows variability, with a main peak of (38 ± 11) × 10 −8 ph cm −2 s −1 at the beginning of March and two later peaks centered on September 8 and November 13. The first γ-ray peak appears to be associated with the peak in the core polarized emission at 43 GHz, as well as with the total intensity light curve. A discrete correlation function analysis yields a correlation coefficient of 0.54 at zero delay, with a significance level > 99.7%. Conclusions. With this multi-frequency study, we accurately determine the polarization properties of Mrk 421, both in the core and in the jet region. The radio and γ-ray light curves are correlated. The observed EVPA variability at 15 GHz is partly due to opacity and partly to a variable Faraday rotation effect. To explain the residual variability of the intrinsic polarization angle and the low degree of polarization in the core region, we invoke a blend of variable cross-polarized subcomponents with different polarization properties within the beam.

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Radio monitoring of a sample of X-and $\vec{\gamma}$-ray loud blazars

Cited by 31 publications

References 16 publications

The role of viscosity in AGN outflows in relation to jet periodicities

The role of viscosity in AGN outflows in relation to jet periodicities

VLBI imaging and optical variability of the BL Lac object OQ 530 (B1418+546)

Very Long Baseline Polarimetry and the Gamma-ray connection in Markarian 421 during the broadband campaign in 2011

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