Revealing the Nature of Blazar Radio Cores through Multifrequency Polarization Observations with the Korean VLBI Network

Park, Jong Ho; Kam, Minchul; Trippe, Sascha; Kang, Sincheol; Byun, Do-Young; Kim, Dae-Won; Algaba, Juan Carlos; Lee, Sang-Sung; Zhao, Guang-Yao; Kino, Motoki; Shin, Naeun; Hada, Kazuhiro; Lee, Taeseok; Oh, Junghwan; Hodgson, Jeffrey A.; Sohn, Bong Won

doi:10.3847/1538-4357/aac490

Cited by 26 publications

(42 citation statements)

References 119 publications

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“…We interpret this shift as a sign of Faraday rotation, and plot the values of these maxima relative to the square of wavelength in the bottom panel of the same figure. The values of the rotation measure (RM) obtained in this way for the pairs of frequencies 10 5.6 -229 GHz, 229-86 GHz, and 86-43 GHz are, correspondingly, −35100 ± 3000, −7900 ± 1000, and −1900 ± 500 rad·m −2 . Neither the signs nor frequency dependence of the RM contradict earlier determinations (see, e.g., Kang et al 2015;Park et al 2018). Figure 17 shows the dependencies of the optical PD on Rband flux density for different stages of activity (1)-(4), as defined in $ 3.6.…”

Section: Relationship Between Multiwavelength Variability and Changesmentioning

confidence: 63%

Multiwavelength behaviour of the blazar 3C 279: decade-long study from γ-ray to radio

Ларионов

Jorstad

Marscher

et al. 2020

Monthly Notices of the Royal Astronomical Society

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We report the results of decade-long (2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015)(2016)(2017)(2018) γ-ray to 1 GHz radio monitoring of the blazar 3C 279, including GASP/WEBT, Fermi and Swift data, as well as polarimetric and spectroscopic data. The X-ray and γ-ray light curves correlate well, with no delay > ∼ 3 hours, implying general co-spatiality of the emission regions. The γ-ray-optical flux-flux relation changes with activity state, ranging from a linear to a more complex dependence. The behaviour of the Stokes parameters at optical and radio wavelengths, including 43 GHz VLBA images, supports either a predominantly helical magnetic field or motion of the radiating plasma along a spiral path. Apparent speeds of emission knots range from 10 to 37c, with the highest values requiring bulk Lorentz factors close to those needed to explain γ-ray variability on very short time scales. The Mg II emission line flux in the 'blue' and 'red' wings correlates with the optical synchrotron continuum flux density, possibly providing a variable source of seed photons for inverse Compton scattering. In the radio bands we find progressive delays of the most prominent light curve maxima with decreasing frequency, as expected from the frequency dependence of the τ = 1 surface of synchrotron self-absorption. The global maximum in the 86 GHz light curve becomes less prominent at lower frequencies, while a local maximum, appearing in 2014, strengthens toward decreasing frequencies, becoming pronounced at ∼ 5 GHz. These tendencies suggest different Doppler boosting of stratified radio-emitting zones in the jet.

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Section: Relationship Between Multiwavelength Variability and Changesmentioning

confidence: 63%

Multiwavelength behaviour of the blazar 3C 279: decade-long study from γ-ray to radio

Ларионов

Jorstad

Marscher

et al. 2020

Monthly Notices of the Royal Astronomical Society

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“…If the Faraday screen is placed in the immediate vicinity of the jet, e.g., like a sheath surrounding the jet as claimed for other distant AGNs (e.g., Zavala & Taylor 2004;Jorstad et al 2007;O'Sullivan & Gabuzda 2009;Hovatta et al 2012;Park et al 2018), then one expects significant RM gradients across the jet with a possible change of the sign of the RM; this is seen in numerical simulations (Broderick & McKinney 2010). This signature has indeed been frequently observed in the jets of many blazars (e.g., Asada et al 2002Asada et al , 2008Gabuzda et al 2004Gabuzda et al , 2018Hovatta et al 2012).…”

Section: A Jet Sheathmentioning

confidence: 99%

Faraday Rotation in the Jet of M87 inside the Bondi Radius: Indication of Winds from Hot Accretion Flows Confining the Relativistic Jet

Park

Hada

Kino

et al. 2019

ApJ

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We study Faraday rotation in the jet of M87 inside the Bondi radius using eight Very Long Baseline Array data sets, one at 8 GHz, four at 5 GHz, and three at 2 GHz. We obtain Faraday rotation measures (RMs) measured across the bandwidth of each data set. We find that the magnitude of RM systematically decreases with increasing distance from the black hole from 5,000 to 200,000 Schwarzschild radii. The data, showing predominantly negative RM sign without significant difference of the RMs on the northern and southern jet edges, suggest that the spatial extent of the Faraday screen is much larger than the jet. We apply models of hot accretion flows, thought to be prevalent in active galactic nuclei having relatively low luminosity such as M87, and find that the decrease of RM is described well by a gas density profile ρ ∝ r −1 . This behavior matches the theoretically expected signature of substantial winds, nonrelativistic un-collimated gas outflows from hot accretion flows, which is consistent with the results of various numerical simulations. The pressure profile inferred from the density profile is flat enough to collimate the jet, which can result in gradual acceleration of the jet in a magneto-hydrodynamical process. This picture is in good agreement with the observed gradual collimation and acceleration of the M87 jet inside the Bondi radius. The dominance of negative RMs suggests that jet and wind axis are misaligned such that the jet emission exposes only one side of the toroidal magnetic fields permeating the winds.

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“…Note that significant progress in blazar polarimetry has also been obtained from radio facilities in mm/submm bands (86/129/230/300 GHz), thanks to the advent of ALMA as well as KVN/GMVA. In particular, recent mm/submm RM measurements of blazars consistently show a systematic increase of RM magnitude towards higher frequencies [162,183,184], reaching as high as 10 5−8 rad m −2 , which are at least ∼2-5 orders of magnitude higher than those typically measured at low frequencies. This strongly indicates the existence of dense Faraday screens and/or strong, highly-ordered B-fields towards the jet base, as expected by magnetic-driven jet models.…”

Section: Polarimetric Propertiesmentioning

confidence: 76%

“…A systematic KVN study for a sample of γ-ray blazars find that the core spectra in their samples systematically become steeper at 86-129 GHz, implying that the fully optically thin regime of the jet base is beginning to be accessed at these frequencies [161]. Furthermore, Park et al [162] have found a systematic increase of RM magnitude with increasing frequency in the mm-wave core of several brightest blazars, indicating a greater B-field strength and electron densities towards the jet base.…”

Section: The Innermost Regions Of Blazarsmentioning

confidence: 99%

Relativistic Jets from AGN Viewed at Highest Angular Resolution

Hada

2019

Galaxies

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Accreting supermassive black holes in active galactic nuclei (AGN) produce powerful relativistic jets that shine from radio to GeV/TeV γ-rays. Over the past decade, AGN jets have extensively been studied in various energy bands and our knowledge about the broadband emission and rapid flares are now significantly updated. Meanwhile, the progress of magnetohydrodynamic simulations with a rotating black hole have greatly improved our theoretical understanding of powerful jet production. Nevertheless, it is still challenging to observationally resolve such flaring sites or jet formation regions since the relevant spatial scales are tiny. Observations with very long baseline interferometry (VLBI) are currently the only way to directly access such compact scales. Here we overview some recent progress of VLBI studies of AGN jets. As represented by the successful black hole shadow imaging with the Event Horizon Telescope, the recent rapid expansion of VLBI capability is remarkable. The last decade has also seen a variety of advances thanks to the advent of RadioAstron, GMVA, new VLBI facilities in East Asia as well as to the continued upgrade of VLBA. These instruments have resolved the innermost regions of relativistic jets for a number of objects covering a variety of jetted AGN classes (radio galaxies, blazars, and narrow-line Seyfert 1 galaxies), and the accumulated results start to establish some concrete (and likely universal) picture on the collimation, acceleration, recollimation shocks, magnetic field topology, and the connection to high-energy flares in the innermost part of AGN jets.

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Revealing the Nature of Blazar Radio Cores through Multifrequency Polarization Observations with the Korean VLBI Network

Cited by 26 publications

References 119 publications

Multiwavelength behaviour of the blazar 3C 279: decade-long study from γ-ray to radio

Multiwavelength behaviour of the blazar 3C 279: decade-long study from γ-ray to radio

Faraday Rotation in the Jet of M87 inside the Bondi Radius: Indication of Winds from Hot Accretion Flows Confining the Relativistic Jet

Relativistic Jets from AGN Viewed at Highest Angular Resolution

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