C. Degli Agosti | Searcharxiv

arXiv2026

Parsec-scale polarimetry and kinematics of a spine-sheath jet in the neutrino-blazar TXS 0506+056

In 2017, the blazar TXS 0506+056 showed a remarkable gamma-ray outburst simultaneously with a high-energy neutrino detection by IceCube from the same sky region. The significance of this association was found to be on the order of 3 sigma thus providing a strong link between the neutrino emission and the blazar flare. The high-energy flare in TXS 0506+056 was followed by a delayed radio flare, peaking in $\sim2020$ in the aftermath of the neutrino event. We investigate the parsec-scale jet structure and dynamics of TXS 0506+056 using 15 GHz full-polarization VLBI observations obtained between 2009 and 2025 with the Very Long Baseline Array. Our kinematic analysis reveals moderate superluminal jet speeds of $\sim(1-2)$c and two quasi-stationary components. A new jet component with comparable speed was ejected contemporaneously with the 2017 IceCube neutrino event. The stacked polarization map is consistent with a stratified spine-sheath jet structure: an inner spine with EVPA aligned with the jet, surrounded by a sheath layer with perpendicular EVPA. Variability in total intensity and polarization further indicates interaction between these layers, particularly evident in characteristic linear polarization flares, associated with EVPA rotations of the quasi-stationary components. The multi-layered jet configuration is consistent with previous studies that were able to explain the neutrino emission in this TXS 0506+056 through a spine-sheath jet structure. We suggest that TXS 0506+056 represents an archetypal case and that similar polarization signatures and geometric light curve flares may be present in other neutrino-emitting sources, potentially offering a solution to the Doppler-crisis phenomenon observed in TeV-emitting blazars.

astro-ph.HE↗

arXiv2025

The WISSH quasar project. XII. X-ray view of the most luminous quasi-stellar objects at Cosmic Noon

To improve our knowledge of nuclear emission in luminous QSOs at Cosmic Noon, we studied the X-ray emission of the WISE/SDSS-selected hyper-luminous (WISSH) QSO sample: 85 broad-line AGN with $L_{bol}>few\times 10^{47}\,erg\,s^{-1}$ at $z\sim 2-4$. Our aim is to characterise their X-ray spectra and explore relations between X-ray luminosity and other bands, comparing powerful QSOs with the general AGN population. We performed spectral analysis for about half of the sample; 16 sources were analysed via their hardness ratio; for the others we estimated their intrinsic luminosity $L_{2-10\,keV}$. Only 8 sources are undetected. We report a large dispersion in $L_{2-10\,keV}$ despite the narrow distribution of $L_{bol}$, $L_{2500\,Å}$ and $λL_{6\,μm}$ (about one-third of the sources classified as X-ray weak). This suggests differences in X-ray corona and accretion flow physics between hyper-luminous and less powerful AGN. X-ray photon index distribution is consistent with that of lower-$z$, lower-$L_{bol}$ AGN, and does not depend on the Eddington ratio ($λ_{Edd}$) or X-ray weakness. Most WISSH QSOs with intrinsic absorption estimates show little to no obscuration ($N_H \le 5\times 10^{22}\,cm^{-2}$). Among the obscured sources we find blue QSOs without broad absorption lines within the "forbidden region" of the $Log(N_H)-Log(λ_{Edd})$ plane, typically occupied by dust-reddened QSOs and associated with intense feedback. We confirm a correlation between $L_{2-10\,keV}$ and CIV line blueshift, a tracer of nuclear ionized outflows. Multi-wavelength data and complete X-ray coverage enabled the investigation of the disk-corona interplay at the highest luminosity regimes. The broad distribution of bolometric correction and X-ray - to - optical index suggest caution when using $L_{bol}$, $L_{2500\,Å}$ or $L_{6\,μm}$ as direct X-ray proxy for individual luminous QSOs.

astro-ph.GA↗