Spectral Evolution of the Parsec‐Scale Jet in the Quasar 3C 345

Lobanov, A.; Zensus, J. A.

doi:10.1086/307555

Cited by 82 publications

(127 citation statements)

References 32 publications

(38 reference statements)

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“…In general, there are two approaches to the extraction of the spectral parameters, one based on the flux densities in each pixel (Lobanov 1998a) and the other one on the fitted components (Lobanov & Zensus 1999;Savolainen et al 2008). The advantage of the pixel-based approach is that it provides a continuous evolution of the spectral values along the jet.…”

Section: Spectral Analysismentioning

confidence: 99%

“…Assuming adiabatic expansion losses as the main energy loss mechanism, and following Marscher & Gear (1985); Lobanov & Zensus (1999), the slope in the ν m −S m plane is given by with b the exponent for the evolution of the magnetic field intensity (B ∝ R −b ), k the exponent for the evolution of the normalization coefficient of the relativistic electron distribution (K ∝ R −k ), d the exponent for the evolution of the Doppler factor (δ ∝ R −d ), and s the spectral slope (N = Kγ −s ). A power law fit to the variation in the turnover flux-density with respect to the turnover frequency provides an exponent η = 0.8 ± 0.1 (see Fig.…”

Section: Core Region In May 2005mentioning

confidence: 99%

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Catching the radio flare in CTA 102

Fromm

Ros

Perucho

et al. 2013

A&A

104

110

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Context. The temporal and spatial spectral evolution of the jets of active galactic nuclei (AGN) can be studied with multi-frequency, multi-epoch very-long-baseline-interferometry (VLBI) observations. The combination of both morphological (kinematical) and spectral parameters can be used to derive source-intrinsic physical properties, such as the magnetic field and the nonthermal particle density. Such a study is of special interest during the high states of activity in AGNs, since VLBI observations can provide estimates of the location of the flaring site. Furthermore, we can trace the temporal variations in the source-intrinsic parameters during the flare, which may reflect the interaction between the underlying plasma and a traveling shock wave. The source CTA 102 exhibited such a radio flare around 2006. Aims. In the first two papers of this series (Papers I and II), we analyzed the single-dish light curves and the VLBI kinematics of the blazar CTA 102 and suggested a shock-shock interaction between a traveling and a standing shock wave as a possible scenario to explain the observed evolution of the component associated to the 2006 flare. In this paper we investigate the core shift and spectral evolution to test our hypothesis of a shock-shock interaction. Methods. We used eight multi-frequency Very Long Baseline Array (VLBA) observations to analyze the temporal and spatial evolution of the spectral parameters during the flare. We observed CTA 102 between May 2005 and April 2007 using the VLBA at six different frequencies spanning from 2 GHz up to 86 GHz. After the calibrated VLBA images were corrected for opacity, we performed a detailed spectral analysis. We developed methods for aligning the images and extracting the uncertainties in the spectral parameters. From the derived values we estimated the magnetic field and the density of the relativistic particles and combined those values with the kinematical changes provided from the long-term VLBA monitoring (Paper II) and single-dish measurements (Paper I).Results. The detailed analysis of the opacity shift reveals that the position of the jet core is proportional to ν −1 with some temporal variations. The value suggests possible equipartition between magnetic field energy and particle kinetic energy densities at the most compact regions. From the variation in the physical parameters we deduced that the 2006 flare in CTA 102 is connected to the ejection of a new traveling feature (t ej = 2005.9) and to the interaction between this shock wave and a stationary structure (interpreted as a recollimation shock) around 0.1 mas from the core (de-projected 18 pc at a viewing angle of ϑ = 2.6 • ). The source kinematics, together with the spectral and structural variations, can be described by helical motions in an overpressured jet.

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Section: Spectral Analysismentioning

confidence: 99%

Section: Core Region In May 2005mentioning

confidence: 99%

Catching the radio flare in CTA 102

Fromm

Ros

Perucho

et al. 2013

A&A

104

110

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“…In flat spectrum radio quasars (FSRQs), such as 3C 345, the component flux decay is commonly driven by radiative losses (Lobanov & Zensus 1999;Jorstad et al 2005), which was assumed in Sect. 3.1.1 without any additional justification.…”

Section: Jet Intensity Gradientmentioning

confidence: 99%

“…: Biretta et al 1986;Baath et al 1992;Lobanov 1996;Zensus et al 1995;Ros et al 2000;Klare 2004;Jorstad et al 2007). On the basis of previous observations, spectral index and turnover frequency distributions have been obtained (Lobanov 1996(Lobanov , 1998aRos et al 2000), the spectral evolution of the jet has been studied (Lobanov & Zensus 1999), the properties of the radio and X-ray emission have been related (Unwin et al 1997;Lobanov & Roland 2005), the dynamics of the central region has been investigated (Lobanov & Roland 2005) and opacity in the nuclear region has been used to determine the physical properties and matter composition of the compact jet (Lobanov 1998b;Hirotani 2005). Quasi-periodic variations in the emission have been detected in the optical (Babadzhanyants & Belokon 1984;Kidger & Takalo 1990) and radio (Aller et al 1996;Teräsranta et al 1998;Lobanov & Zensus 1999) regimes with a possible periodicity of 3.5-4.5 years and major flares occurring every 8-10 years.…”

Section: Introductionmentioning

confidence: 99%

Relativistic outflow drivesγ-ray emission in 3C 345

Schinzel

Lobanov

Taylor

et al. 2012

A&A

100

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Aims. On the basis of the first 20 months of Fermi-LAT data and optical monitoring, the quasar 3C 345 has been identified as a γ-ray emitter. We investigate whether there is a connection between the γ-ray and optical variability of 3C 345 and the properties of its parsec-scale radio emission. Methods. We combined the Fermi-LAT data of 3C 345, covering an energy range of 0.1-300 GeV, with 32 Very Long Baseline Array observations of the object made at 43.2 GHz in the period of January 2008-March 2010.Results. The VLBA data reveal the morphology and kinematics of the flow on scales of up to ≈5 milliarcseconds (deprojected linear distances of 380 parsecs). The brightness temperature, T b (r), measured along the jet first decreases with distance ∝r −(0.95 ± 0.69) and later exhibits a break at ≈0.3 milliarcseconds (mas), with T b (r) ∝ r −(4.11 ± 0.85) at larger separations. Variations in the γ-ray, optical, and parsec-scale radio emission display a similar long-term trend that persists during the entire VLBA monitoring period. The γ-ray and optical variations on shorter timescales are related to structural changes in the jet on scales of ≈0.3 mas (≈23 parsecs, deprojected), with the γ-ray and optical flares possibly being related to the evolution of four distinct superluminal components identified in the flow. Conclusions. The observations indicate that both the quiescent and flaring components of the γ-ray emission are produced in a region of the jet that extends up to ∼23 pc. This region may correspond to the Compton-loss dominated zone of the flow and its large extent may favor the synchrotron self-Compton mechanism for γ-ray production in the relativistic jet of the quasar 3C 345.

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“…High-resolution VLBI observations offer the unique possibility of studying the structural and spectral evolution in AGN on parsec-scales (e.g., Lobanov & Zensus 1999;Savolainen et al 2002). These observations provide a tool to test several jet models and to probe how variations within the first few parsecs contribute to the high-energy emission.…”

Section: Introductionmentioning

confidence: 99%

Catching the radio flare in CTA 102

Fromm¹,

Ros²,

Perucho³

et al. 2013

A&A

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Context. Very Long Baseline Interferometry (VLBI) observations can resolve the radio structure of active galactic nuclei (AGN) and provide estimates of the structural and kinematic characteristics on parsec-scales in their jets. The changes in the kinematics of the observed jet features can be used to study the physical conditions in the innermost regions of these sources. We performed multifrequency multiepoch Very Long Baseline Array (VLBA) observations of the blazar CTA 102 during its 2006 radio flare, the strongest ever reported for this source. These observations provide an excellent opportunity to investigate the evolution of the physical properties of blazars, especially during these flaring events Aims. We want to study the kinematic changes in the source during the strong radio outburst in April 2006 and test the assumption of a shock-shock interaction. This assumption is based on the analysis and modeling of the single-dish observations of CTA 102 (Paper I). Methods. In this paper we study the kinematics of CTA 102 at several frequencies using VLBI observations. From the modeled jet features we derived estimates for the evolution of the physical parameters, such as the particle density and the magnetic field. Furthermore, we combined our observations during the 2006 flare with long-term VLBA monitoring of the source at 15 GHz and 43 GHz. Results. We cross-identified seven features throughout our entire multifrequency observations and find evidence of two possible recollimation shocks around 0.1 mas (deprojected 18 pc at a viewing angle ϑ = 2.6 • ) and 6.0 mas (deprojected 1 kpc) from the core. The 43 GHz observations reveal a feature ejected at epoch t ej = 2005.9 ± 0.2, which could be connected to the 2006 April radio flare. Furthermore, this feature might be associated with the traveling component involved in the possible shock-shock interaction, which gives rise to the observed double peak structure in the single-dish light curves reported in Paper I.

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Spectral Evolution of the Parsec‐Scale Jet in the Quasar 3C 345

Cited by 82 publications

References 32 publications

Catching the radio flare in CTA 102

Catching the radio flare in CTA 102

Relativistic outflow drivesγ-ray emission in 3C 345

Catching the radio flare in CTA 102

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