Ejection of Double Knots from the Radio Core of PKS 1510–089 during the Strong Gamma-Ray Flares in 2015

Abstract

PKS 1510-089 is a bright and active γ-ray source that showed strong and complex γ-ray flares in mid-2015 during which the Major Atmospheric Gamma Imaging Cherenkov telescopes detected variable very high energy (VHE; photon energies >100 GeV) emission. We present long-term multi-frequency radio, optical, and γ-ray light curves of PKS 1510-089 from 2013 to 2018, and results of an analysis of the jet kinematics and linear polarization using 43 GHz Very Long Baseline Array data observed between late 2015 and mid-2017. We find that a strong radio flare trails the γ-ray flares in 2015, showing an optically thick spectrum at the beginning and becoming optically thin over time. Two laterally separated knots of emission are observed to emerge from the radio core nearly simultaneously during the γ-ray flares. We detect an edge-brightened linear polarization near the core in the active jet state in 2016, similar to the quiescent jet state in 2008-2013. These observations indicate that the γ-ray flares may originate from compression of the knots by a standing shock in the core and the jet might consist of multiple complex layers showing time-dependent behavior, rather than of a simple structure of a fast jet spine and a slow jet sheath.

Jet Collimation and Acceleration in the Giant Radio Galaxy NGC 315

“…et al. 2005;Tavecchio & Ghisellini 2008Marscher et al 2010;MacDonald et al 2015;Park et al 2019c). Also, Nakahara et al (2018) explained the observed jet radii for NGC 4261 (Nakahara et al 2018) and Cygnus A (Boccardi et al 2016b;Nakahara et al 2019) being systematically larger than those for M87 and NGC 6251 (see Figure 8 in Nakahara et al 2018) with the spinesheath scenario.…”

Multiwavelength analysis and the difference in the behavior of the spectral features during the 2010 and 2014 flaring periods of the blazar 3C 454.3

“…The variability of the spectral index indicates variations of intricate source properties, most likely changes in the optical depth (Trippe et al 2011). Along the same lines, Park et al (2019) interpreted that when the radio spectra are optically thick an emerging component is close to the core and when the spectra become optically thin the component is well separated from the core. This interpretation describes well what happened during the FP1 and is compatible with the shock-injet model (e.g.…”

“…This model has been invoked to explain the origin of gammaray flares in PKS 1510-089 (e.g. Marscher et al 2010;Park et al 2019). Particularly, the gamma-ray flare of 2015 of this object was found to have origin at ∼10 pc from the base of the jet.…”

“…Particularly, the gamma-ray flare of 2015 of this object was found to have origin at ∼10 pc from the base of the jet. Park et al (2019) attempted to explain this with the spine-sheath model, however, they suggest that for this particular case the jet might consist of multiple layers (not only a fast spine and a slow sheath). A toy model of a spine-sheath structured jet has been developed for FSRQs by Sikora et al (2016), they demonstrate that it provides a natural explanation for the hardness and the extreme Compton dominance of the gamma-ray flares, and the weaker fractional flux variations of the optical band than those in gamma-rays.…”

Interferometric Monitoring of Gamma-ray Bright AGNs: S5 0716+714

“…We can do this by measuring the turnover frequency and the flux density, and the size of the source at the turnover frequency (Rybicki & Lightman 1986). In previous studies using the Interferometric Monitoring of GAmma-ray Bright AGNs (iMOGABA) program (Lee et al 2013(Lee et al , 2016b(Lee et al , 2017aAlgaba et al 2018a,b;Kim et al 2018;Park et al 2019) which is a part of the Korean VLBI Network (KVN) key science programs, magnetic field strengths of a few mG were found in the SSA regions of the relativistic jets in S5 0716+714 (Lee et al 2017a) and 1633+382 (Algaba et al 2018a).…”