A multiwavelength view of BL Lacs neutrino candidates

TL;DR

This study investigates BL Lac objects as potential neutrino sources by analyzing their spectral energy distributions and temporal behavior, aiming to identify electromagnetic counterparts to IceCube neutrino detections.

Contribution

It presents a multiwavelength observational campaign of BL Lacs spatially correlated with IceCube neutrinos, including a new source addition and detailed SED characterization, highlighting potential extreme blazar candidates.

Findings

Better characterization of BL Lac spectral energy distributions.

Identification of a peculiar low synchrotron peak source.

No clear gamma-ray activity pattern around neutrino events.

Abstract

The discovery of high-energy astrophysical neutrinos by IceCube kicked off a new line of research to identify the electromagnetic counterparts producing these neutrinos. Among the extragalactic sources, active galactic nuclei (AGN), and in particular Blazars, are promising candidate neutrino emitters. Their structure, with a relativistic jet pointing to the Earth, offers a natural accelerator of particles and for this reason a perfect birthplace of high energy neutrinos. A good characterisation of the spectral energy distribution (SED) of these sources can improve the understanding of the physical composition of the source and the emission processes involved. Starting from our previous works in which we assumed a correlation between the $\gamma$-ray and the neutrino flux of the BL Lacs of the 2FHL catalogue (detected by Fermi above 50GeV), we select those BL Lac in spatial correlation with the IceCube events. We obtain a sample of 7 sources and we start an observational campaign to have a better characterisation of the synchrotron peak. During the analysis of the data a new source has been added because of its position inside the angular uncertainty of a muon track event detected by IceCube. This source, namely TXS0506+056, was in a high-state during the neutrino event and we will consider it as benchmark to check the proprieties of the other sources of the sample during the related neutrino detection. We obtain a better characterisation of the SED for the sources of our sample. A prospective extreme Blazar, a very peculiar low synchrotron peak (LSP) source with a large separation of the two peaks and a \textit{twin} of TXS0506+056 come up. We also provide the $\gamma$-ray light curve to check the trend of the sources around the neutrino detection but no clears patterns are in common among the sources.