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Register a new userTracking the curved jet in PKS 1502+106
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We carried out a multifrequency and multiepoch study of the highly polarized quasar, PKS 1502+106 at radio frequencies. The analysis is based on an EVN dataset at 5 GHz, archive VLBA datasets at 2.3, 8.3, 24.4 and 43.1 GHz and an archive MERLIN dataset at 5 GHz. The various datasets span over a period of 10 years. The source is characterized by a multi-component one-sided jet at all epochs. The VLBI images show that a complex curved jet is located to the southeast and east of the core, with the position angle (PA) of the jet axis wiggling between 80 deg and 130 deg. The MERLIN image reveals that the jet extends to 0.6 arcsec at a PA 135+-12 degr. The radio core in the VLBI images has a brightness temperature approaching the equipartition limit, indicating highly relativistic plasma beamed towards us. Delta PA in the source, the misalignment of the kpc- and pc-scale radio structure, is estimated about 32 degr, suggesting that PKS 1502+106 belongs to the aligned population. Four superluminal components are detected in the parsec scale jet, whose velocities are 24.2 h{-1}c, 14.3 h{-1}c, 6.8 h{-1}c and 18.1 h{-1}c. Our analysis supports the idea that the relativistic jet in PKS 1502+106 is characterised by extreme beaming and that its radio properties are similar to those of gamma-ray loud sources.
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Blazars are among the most variable objects in the universe. They feature energetic jets of plasma that launch from the cores of these active galactic nuclei (AGN), triggering activity from radio up to gamma-ray energies. Spatial localization of the region of their MeV/GeV emission is a key question in understanding the blazar phenomenon. The flat spectrum radio quasar (FSRQ) PKS 1502+106 has exhibited extreme and correlated, radio and high-energy activity that triggered intense monitoring by the Fermi-GST AGN Multi-frequency Monitoring Alliance (F-GAMMA) program and the Global Millimeter VLBI Array (GMVA) down to $lambda$3 mm (or 86 GHz), enabling the sharpest view to date towards this extreme object. Here, we report on preliminary results of our study of the gamma-ray loud blazar PKS 1502+106, combining VLBI and single dish data. We deduce the critical aspect angle towards the source to be $theta_{rm c} = 2.6^{circ}$, calculate the apparent and intrinsic opening angles and constrain the distance of the 86 GHz core from the base of the conical jet, directly from mm-VLBI but also through a single dish relative timing analysis. Finally, we conclude that gamma rays from PKS 1502+106 originate from a region between ~1-16 pc away from the base of the hypothesized conical jet, well beyond the bulk of broad-line region (BLR) material of the source.
The origin of the multi-band activities (outbursts/flares) of blazars is still a heavily debated topic. Shock and magnetic reconnection have long been considered as possible triggers for the multi-band activities. In this paper, we present an exploration of the origin of multi-band activities for a high-redshift (z =1.8385) FSRQ PKS 1502+106. Utilizing multi-band data from radio to $gamma$-ray and optical polarization observations, we investigate two dramatic activities in detail: a $gamma$-ray dominated outburst in 2015 and an optical dominated outburst in 2017. Our main results are as follows. (I) A fast $gamma$-ray flare with a flux-doubling time-scale as short as 1-hr in 2015 is discovered. Based on the variability time-scale, the physical parameters of the flaring region (e.g, minimum Doppler factor, emission region size, etc.) are constrained. At the peak of the flare, the $gamma$-ray spectrum hardens to $Gamma_{gamma} = 1.82pm0.04$ and exhibits an obvious curvature/break characteristic that is caused by the typical cooling break. Modelings of multi-band SEDs reveal a very hard electronic energy spectrum with the electronic spectral index of $1.07pm0.53$. This result suggests that this fast $gamma$-ray flare may be triggered by magnetic reconnection. (II) During the outburst in 2017, the optical polarization degree and optical fluxes show a very tight correlation. By analyzing Stokes parameters of polarization observations, our results show that this outburst could be triggered by a transverse shock with a compression ratio of $eta> 2.2$, and the magnetic field intensity of the shock emission region is about $0.032$ G.
On July 30th, 2019 IceCube detected a high-energy astrophysical muon neutrino candidate, IC-190730A, with a $67%$ probability of astrophysical origin. The flat spectrum radio quasar (FSRQ) PKS 1502+106 is in the error circle of the neutrino. Motivated by this observation, we investigate whether the emission of IC-190730A from this source is plausible, considering the multi-wavelength (infrared/UV/optical/X-ray/gamma-ray) emission of PKS 1502+106 at the time of the neutrino arrival. We analyse UV/optical and X-ray data and collect additional observations from the literature to construct the multi-wavelength spectral energy distribution of PKS 1502+106. We perform leptohadronic modelling of the multi-wavelength emission of the source and determine the most plausible emission scenarios and the maximum expected accompanying neutrino flux. A model in which the multi-wavelength emission of PKS 1502+106 originates beyond the broad-line region and inside the dust torus is most consistent with the observations. In this scenario, PKS 1502+106 can have produced up to of order one muon neutrino with energy exceeding 100 TeV in the lifetime of IceCube. An appealing feature of this model is that the required proton luminosity is consistent with the average required proton luminosity if blazars power the observed ultra-high-energy-cosmic-ray flux and well below the sources Eddington luminosity. If such a model is ubiquitous among FSRQs, additional neutrinos can be expected from other bright sources with energy $gtrsim 10$ PeV.
We report the discovery of an extremely curved jet in the radio-loud quasar PKS2136+141. Multi-frequency Very Long Baseline Array (VLBA) images show a bending jet making a turn-around of 210 degrees in the plane of the sky, which is, to our knowledge, the largest ever observed change in the position angle of an astrophysical jet. Images taken at six different frequencies, from 2.3 to 43 GHz, reveal a spiral-like trajectory, which is likely a sign of an intrinsic helical geometry. A space-VLBI image, taken with the HALCA satellite at 5 GHz and having comparable resolution to our ground-based 15 GHz data, confirms that the bend is a frequency-independent structure. VLBA monitoring data at 15 GHz, covering eight years of observations, show knots in the jet clearly deviating from ballistic motion, which suggests that the bending may be caused by a growing helical Kelvin-Helmholtz normal mode. The jet appearance suggests a helical wave at a frequency well below the resonant frequency of the jet, which indicates that the wave is driven by a periodic perturbation at the base of the jet. We fit the observed structure in the source with a helical twist, and we find that a simple isothermal model with a constant wave speed and wavelength gives a good fit. The measured apparent velocities indicate some degree of acceleration along the jet, which together with an observed change in the apparent half-opening angle of the jet allow us to estimate the changes in the angle between the local jet direction and our line of sight. We suggest that the jet in PKS2136+141 is distorted by a helical Kelvin-Helmholtz normal mode externally driven into the jet (e.g. by precession), and that our line of sight falls within the opening angle of the helix cone.
We report the discovery of an extremely curved jet in the high frequency peaking GPS quasar PKS 2136+141. Our multi-frequency VLBA images show a bending jet making a turn-around of 210 degrees on the plane of the sky, which is, to our knowledge, the largest ever observed change in a structural position angle of an extragalactic jet. Images taken at six different frequencies, from 2 to 43 GHz, beautifully reveal a spiral-like trajectory. We discuss possibilities to constrain the 3-D geometry of the source and suggest that it could be used as a testbed for models describing the bending of the relativistic jets.
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