The relativistic parsec-scale jets of the blazars TXS 0506+056 and PKS 0502+049 and their possible association with gamma-ray flares and neutrino production

Abstract

The physical nature of the mechanism responsible for the emission of neutrinos in active galactic nuclei (AGNs) has been matter of debate in the literature, with relativistic jets of radio-loud AGNs as possible candidates to be the sources of high-energy neutrinos. The most prominent candidate so far is the blazar TXS 0506+056, which is found to be associated with the neutrino event IceCube-170922A. Furthermore, the IceCube reported an excess of neutrinos towards TXS 0506+056 between September 2014 and March 2015, even though this association needs additional investigation, considering the presence of a nearby gamma-ray source, the quasar PKS 0502+049. Motivated by this, we studied the parsec-scale structures of TXS 0506+056 and PKS 0502+049 through radio interferometry at 8 and 15 GHz. We identified twelve jet components in TXS 0506+056 and seven components in PKS 0502+049. The most reliable jet components show superluminal speeds ranging from 9.5c to 66c in the case of TXS 0506+056, and from 14.3c to 59c for PKS 0502+049, which were used to estimate a lower (upper) limit for the Lorentz factor (jet viewing angle) for both sources. A novel approach using simultaneously the brightness temperature of the core region and the apparent speeds of the jet components allowed us to infer basic jet parameters for TXS 0506+056 at distinct epochs. We also found that the emergence of new jet components coincides with the occurrence of gamma-ray flares. Interestingly, two of these coincidences in the case of PKS 0502+049 and one for TXS 0506+056 seems to be correlated with neutrino events detected by the IceCube Observatory.

Multiwavelength and Multimessenger Observations of Blazars and Theoretical Modeling: Blazars as Astrophysical Neutrino Sources

“…2). [49] thus argue that IceCube- 170922A and the 2014 -15 neutrino flare might actually originate from two different blazars. However, it seems that the decomposition of the VLBI images into individual components as well as the identification of components across epochs appears very difficult in the case of these blazars, and superluminal-motion speeds up to > ∼ 60 c have been found for both sources, which should be taken with great caution.…”

“…A very recent finding and suggestion that has so far received little attention in the literature is based on a detailed re-analysis of the pc-scale jet structures using archival 8 and 15 GHz very-long-baseline interferometry data, not only of TXS 0506+056, but also of another nearby γ-ray blazar, namely PKS 0502+049 [49]. Estimating the ejection times of 12 and 7 jet components in TXS 0506+056 and PKS 0502+049, respectively, they find that the arrival time of IceCube-170922A coincides with the estimated ejection times of two components in the jet of TXS 0506+056, while no such coincidence was found for the 2014 -15 neutrino flare.…”

High-Energy Neutrinos from Active Galactic Nuclei

“…214,215 However, the interpretation is still under debate because the radio data are also consistent with a structured jet. [216][217][218] Note that the cascade constraint is applied anyway whether TXS 0506+056 is an atypical blazar or not.…”