4 research outputs found
Parsec-scale evolution of the gigahertz-peaked spectrum quasar PKS 0858-279
We conducted multi-epoch, multi-frequency parsec-scale studies on the
gigahertz-peaked spectrum quasar PKS 0858-279 with the Very Long Baseline Array
(VLBA). Our observations on 2005-11-26 elucidated a weak core, characterized by
an inverted spectrum, and a distinctly bent jet that exhibited a notable bright
feature in its Stokes I emission. Through comprehensive analysis of
polarization and spectral data, we inferred the formation of a shock wave
within this feature, stemming from interactions with a dense cloud in the
ambient medium. In this paper, VLBI-Gaia astrometry further reinforces the core
identification. With a deep analysis of six additional VLBA epochs spanning
from 2007 to 2018, we observed that while the quasar's parsec-scale structure
remained largely consistent, there were discernible flux density changes. These
variations strongly imply the recurrent ejection of plasma into the jet.
Complementing our VLBA data, RATAN-600 observations of the integrated spectra
suggested an interaction between standing and travelling shock waves in 2005.
Moreover, our multi-epoch polarization analysis revealed a drastic drop in
rotation measure values from 6000 rad/m^2 to 1000 rad/m^2 within a single year,
attributable to diminishing magnetic fields and particle density in an external
cloud. This change is likely instigated by a shock in the cloud, triggered by
the cloud's interaction with the jet, subsequently prompting its expansion.
Notably, we also observed a significant change in the magnetic field direction
of the jet, from being perpendicular post its observed bend to being
perpendicular prior to the bend - an alteration possibly induced by the
dynamics of shock waves.Comment: 14 pages, 10 figures, accepted for publication in MNRA
High-energy neutrino-induced cascade from the direction of the flaring radio blazar TXS 0506+056 observed by the Baikal Gigaton Volume Detector in 2021
The existence of high-energy astrophysical neutrinos has been unambiguously
demonstrated, but their sources remain elusive. IceCube reported an association
of a 290-TeV neutrino with a gamma-ray flare of TXS 0506+056, an active
galactic nucleus with a compact radio jet pointing to us. Later, radio blazars
were shown to be associated with IceCube neutrino events with high statistical
significance. These associations remained unconfirmed with the data of
independent experiments. Here we report on the detection of a rare neutrino
event with the estimated energy of 224 +- 75 TeV from the direction of TXS
0506+056 by the new Baikal-GVD neutrino telescope in April 2021 followed by a
radio flare observed by RATAN-600. This event is the highest-energy cascade
detected so far by Baikal-GVD from a direction below horizon. The result
supports previous suggestions that radio blazars in general, and TXS 0506+056
in particular, are the sources of high-energy neutrinos, and opens up the
cascade channel for the neutrino astronomy.Comment: 12 pages, 6 figures, 2 table
Search for directional associations between Baikal Gigaton Volume Detector neutrino-induced cascades and high-energy astrophysical sources
Baikal-GVD has recently published its first measurement of the diffuse
astrophysical neutrino flux, performed using high-energy cascade-like events.
We further explore the Baikal-GVD cascade dataset collected in 2018-2022, with
the aim to identify possible associations between the Baikal-GVD neutrinos and
known astrophysical sources. We leverage the relatively high angular resolution
of the Baikal-GVD neutrino telescope (2-3 deg.), made possible by the use of
liquid water as the detection medium, enabling the study of astrophysical point
sources even with cascade events. We estimate the telescope's sensitivity in
the cascade channel for high-energy astrophysical sources and refine our
analysis prescriptions using Monte-Carlo simulations. We primarily focus on
cascades with energies exceeding 100 TeV, which we employ to search for
correlation with radio-bright blazars. Although the currently limited neutrino
sample size provides no statistically significant effects, our analysis
suggests a number of possible associations with both extragalactic and Galactic
sources. Specifically, we present an analysis of an observed triplet of
neutrino candidate events in the Galactic plane, focusing on its potential
connection with certain Galactic sources, and discuss the coincidence of
cascades with several bright and flaring blazars.Comment: 10 pages, 3 figure