A VLBA survey of the core shift effect in AGN jets

Sokolovsky, K. V.; Kovalev, Y. Y.; Pushkarev, A. B.; Lobanov, A. P.

doi:10.1051/0004-6361/201016072

Cited by 184 publications

(256 citation statements)

References 43 publications

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“…We fixed the value of kr = 1, which is applicable if (i) the dominating absorption mechanism is synchrotron self-absorption, (ii) the jet has a conical shape, and (iii) the equipartition the particle and magnetic field densities holds (see, e.g., Blandford & Königl 1979;Lobanov 1998;Hirotani 2005;Zamaninasab et al 2014;Zdziarski et al 2015). Our observations agree well with kr = 1 (e.g., O'Sullivan & Gabuzda 2009b;Sokolovsky et al 2011;Zdziarski et al 2015). The two-frequency core position offset Ωrν then is given by (Lobanov 1998) …”

Section: Core Shift Analysissupporting

confidence: 79%

“…After fringe fitting, a complex bandpass calibration was made and residual amplitude corrections determined and applied, using AIPS task LPCAL, for a few sub-bands at specific antennas (see Table 2). The estimated accuracy of the VLBA amplitude calibration in the 5-15 GHz frequency range is of ∼5% and at 15-43 GHz of ∼10% (see also Kovalev et al 2005;Sokolovsky et al 2011).…”

Section: Multi-epoch 4-43 Ghz Vlba Observationsmentioning

confidence: 99%

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Multiwavelength observations of the γ-ray flaring quasar S4 1030+61 in 2009–2014

Kravchenko

Kovalev

Hovatta

2016

Mon. Not. R. Astron. Soc.

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We present a study of the parsec-scale multi-frequency properties of the quasar S4 1030+61 during a prolonged radio and γ-ray activity. Observations were performed within Fermi γ-ray telescope, OVRO 40-m telescope and MOJAVE VLBA monitoring programs, covering five years from 2009. The data are supplemented by four-epoch VLBA observations at 5, 8, 15, 24, and 43 GHz, which were triggered by the bright γ-ray flare, registered in the quasar in 2010. The S4 1030+61 jet exhibits an apparent superluminal velocity of (6.4±0.4)c and does not show ejections of new components in the observed period, while decomposition of the radio light curve reveals nine prominent flares. The measured variability parameters of the source show values typical for Fermi-detected quasars. Combined analysis of radio and γ-ray emission implies a spatial separation between emitting regions at these bands of about 12 pc and locates the γ-ray emission within a parsec from the central engine. We detected changes in the value and direction of the linear polarization and the Faraday rotation measure. The value of the intrinsic brightness temperature of the core is above the equipartition state, while its value as a function of distance from the core is well approximated by the power-law. Altogether these results show that the radio flaring activity of the quasar is accompanied by injection of relativistic particles and energy losses at the jet base, while S4 1030+61 has a stable, straight jet well described by standard conical jet theories.

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Section: Core Shift Analysissupporting

confidence: 79%

Section: Multi-epoch 4-43 Ghz Vlba Observationsmentioning

confidence: 99%

Multiwavelength observations of the γ-ray flaring quasar S4 1030+61 in 2009–2014

Kravchenko

Kovalev

Hovatta

2016

Mon. Not. R. Astron. Soc.

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“…For direct interferometric measurements, increasing the interferometer baseline length is the only way to measure higher brightness temperatures (see, e.g., Kovalev et al 2005), and hence, to place stringent observational constraints on the physics of the most energetic relativistic outflows. The highest observing frequency, 22 GHz, and resolution of RadioAstron allow us to probe the most energetic regions located close to the central engine (see, e.g., Lobanov 1998;Sokolovsky et al 2011;Pushkarev et al 2012) while scattering effects in the Galaxy are negligible (Pushkarev & Kovalev 2015).…”

Section: Introductionmentioning

confidence: 99%

PROBING THE INNERMOST REGIONS OF AGN JETS AND THEIR MAGNETIC FIELDS WITH RADIOASTRON. I. IMAGING BL LACERTAE AT 21 μas RESOLUTION

Gómez

Lobanov

Bruni

et al. 2016

ApJ

145

165

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We present the first polarimetric space very long baseline interferometry (VLBI) imaging observations at 22 GHz. BLLacertae was observed in 2013 November 10 with the RadioAstron space VLBI mission, including a ground array of 15 radio telescopes. The instrumental polarization of the space radio telescope is found to be less than 9%, demonstrating the polarimetric imaging capabilities of RadioAstron at 22 GHz. Ground-space fringes were obtained up to a projected baseline distance of 7.9Earth diameters in length, allowing us to image the jet in BLLacertae with a maximum angular resolution of 21 μas, the highest achieved to date. We find evidence for emission upstream of the radio core, which may correspond to a recollimation shock at about 40 μas from the jet apex, in a pattern that includes other recollimation shocks at approximately 100 and 250 μas from the jet apex. Polarized emission is detected in two components within the innermost 0.5 mas from the core, as well as in some knots 3 mas downstream. Faraday rotation analysis, obtained from combining RadioAstron 22 GHz and groundbased 15 and 43 GHz images, shows a gradient in rotation measure and Faraday-corrected polarization vector as a function of position angle with respect to the core, suggesting that the jet in BLLacertae is threaded by a helical magnetic field. The intrinsic de-boosted brightness temperature in the unresolved core exceeds 3 10 12 K, suggesting, at the very least, departure from equipartition of energy between the magnetic field and radiating particles.

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“…These new jet components contribute to the increase in source brightness, and are initially coincident with the bright central component (known as the "core"; see Section 5.1) before gradually moving outwards at speeds of up to 0.5 mas year −1 . VLBI imaging at X-band can only clearly resolve the jet components when they are > 100 µas from the core (Kovalev et al, 2008;Sokolovsky et al, 2011). On the other hand, flux density monitoring (with VLBI or using a single dish) can identify ejection of a new component (by detecting the start of a flare) long before it is seen in VLBI images 5 .…”

Section: Variability Metricsmentioning

confidence: 99%

“…This is known as the core shift effect, and it has been measured through VLBI imaging (e.g. Kovalev et al, 2008;Sokolovsky et al, 2011).…”

Section: The Samplementioning

confidence: 99%

The effects of frequency-dependent quasar variability on the celestial reference frame

Shabala

Rogers

McCallum

et al. 2014

J Geod

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We examine the relationship between source position stability and astrophysical properties of radioloud quasars making up the International Celestial Reference Frame. Understanding this relationship is important for improving quasar selection and analysis strategies, and therefore reference frame stability. We construct flux density time series, known as light curves, for 95 of the most frequently observed ICRF2 quasars at both the 2.3 and 8.4 GHz geodetic VLBI observing bands. Because the appearance of new quasar components corresponds to an increase in quasar flux density, these light curves alert us to potential changes in source structure before they appear in VLBI images.We test how source position stability depends on three astrophysical parameters: (1) Flux density variability at X-band; (2) Time lag between flares in S and X-bands; (3) Spectral index rms, defined as the variability in the ratio between S and X-band flux densities. We find that the time lag between S and X-band light curves provides a good indicator of position stability: sources with time lags less than 0.06 years are significantly more stable (> 20 percent improvement in weighted rms) than sources with larger time lags. A similar improvement is obtained by observing sources with low (< 0.12) spectral index variability. On the other hand, there is no strong dependence of source position stability on flux density variability in a single frequency band. These findings can be understood by interpreting the time lag between S and X-band light curves as a measure of the size of the source structure. Monitoring of source flux density at multiple frequencies therefore appears to provide a useful probe of quasar structure on scales important to geodesy. The observed astrometric position of the brightest quasar component (the core) is known to depend on observing frequency. We show how multi-frequency flux density monitoring may allow the dependence on frequency of the relative core positions along the jet to be elucidated. Knowledge of the position-frequency relation has important implications for current and future geodetic VLBI programs, as well as the alignment between the radio and optical celestial reference frames.

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A VLBA survey of the core shift effect in AGN jets

Cited by 184 publications

References 43 publications

Multiwavelength observations of the γ-ray flaring quasar S4 1030+61 in 2009–2014

Multiwavelength observations of the γ-ray flaring quasar S4 1030+61 in 2009–2014

PROBING THE INNERMOST REGIONS OF AGN JETS AND THEIR MAGNETIC FIELDS WITH RADIOASTRON. I. IMAGING BL LACERTAE AT 21 μas RESOLUTION

The effects of frequency-dependent quasar variability on the celestial reference frame

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