Observing the inner parsec-scale region of candidate neutrino-emitting blazars

Abstract

Context. Many questions on the nature of astrophysical counterparts of high-energy neutrinos remain unanswered. There is increasing evidence of a connection between blazar jets and neutrino events, with the flare of the gamma-ray blazar TXS0506+056 in spatial and temporal proximity of IC170922A representing one of the most outstanding associations of high-energy neutrinos with astrophysical sources reported so far. Aims. With the purpose of characterising potential blazar counterparts to high-energy neutrinos, we analysed the parsec-scale regions of gamma-ray blazars in spatial coincidence with neutrinos detected by IceCube. Specifically, we intended to investigate peculiar radio properties of the candidate counterparts related to neutrino production, as radio flares coincident to the neutrino detection or features in jets morphology (limb brightening, transverse structures). Methods. We collected multi-frequency VLBI follow-up observations of candidate counterparts of four high-energy neutrino events detected by IceCube between January 2019 and November 2020. We analysed their radio characteristics soon after the neutrino arrival in comparison with archival VLBI observations and low-frequency radio observations. We discussed our results with respect to previous statistical works and studies on the case of TXS 0506+056. Results. We identified and analysed in detail five potential neutrino emitting blazars. Our results suggest an enhanced state of radio activity for one source, PKS1725+123. However, the lack of adequate monitoring prior to the neutrino events was a limitation in tracing radio activity and morphological changes in all the sources. Conclusions. We suggest that PKS1725+123 is a promising neutrino source candidate. For the other four sources, our results alone do not allow us to reveal a strong connection between the radio activity state at neutrino arrival.

22 pages, 6 figures, accepted for publication in A&A

References in corpus (22)

• Time-integrated Neutrino Source Searches with 10 years of IceCube Data
• MOJAVE: XV. VLBA 15 GHz Total Intensity and Polarization Maps of 437 Parsec-Scale AGN Jets From 1996-2017
• The contribution of Fermi-2LAC blazars to the diffuse TeV-PeV neutrino flux
• A tidal disruption event coincident with a high-energy neutrino
• MOJAVE. XVII. Jet Kinematics and Parent Population Properties of Relativistically Beamed Radio-Loud Blazars
• Observational evidence for the origin of high-energy neutrinos in parsec-scale nuclei of radio-bright active galaxies
• Directional association of TeV to PeV astrophysical neutrinos with radio blazars
• 2WHSP: A catalog of HE and VHE gamma-ray blazars and blazar candidates
• High-Energy Neutrino and Gamma-Ray Emission from Tidal Disruption Events
• Particle acceleration in astrophysical jets
• Structured jets in BL Lac objects: efficient PeV neutrino factories?
• Association of IceCube neutrinos with radio sources observed at Owens Valley and Metsähovi Radio Observatories
• Multi-wavelength and neutrino emission from blazar PKS 1502+106
• High-energy cosmic ray nuclei from tidal disruption events: Origin, survival, and implications
• 1WHSP: an IR-based sample of $\sim$1,000 VHE $\gamma$-ray blazar candidates
• Electron-proton co-acceleration on relativistic shocks in extreme-TeV blazars
• A concordance scenario for the observed neutrino from a Tidal Disruption Event
• Apparent superluminal core expansion and limb brightening in the candidate neutrino blazar TXS 0506+056
• Cosmic neutrinos from temporarily gamma-suppressed blazars
• The Spectra of IceCube Neutrino (SIN) candidate sources -- II. Source Characterisation
• On the relative importance of hadronic emission processes along the jet axis of Active Galactic Nuclei
• The parsec-scale jet of the neutrino-emitting blazar TXS~0506+056

Cited by in corpus (1)

• Growing evidence for high-energy neutrinos originating in radio blazars