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KM3NeT/ARCA stacking search for high-energy neutrinos from blazars

Francesco Carenini, Giulia Illuminati

TL;DR

This work targets high-energy neutrinos from HBL blazars using KM3NeT/ARCA in configurations with 6–21 DUs. It combines a physically motivated one-zone lepto-hadronic flux model (via LeHa-Paris) with a binned, two-dimensional stacking likelihood across 232 3HSP HBLs, deriving flux templates by rescaling the PKS 2155-304 best-fit flux and redshift scaling to place the spectral peak at $E_\nu \sim 10^{17}$ eV. Background is estimated from scrambled data and IRFs provide the signal templates; the analysis finds no significant excess ($p=0.074$, $1.44\sigma$) and sets 90% CL upper limits on the stacked flux, illustrating the approach's potential as KM3NeT/ARCA expands and models are refined. The results underscore the value of physically motivated population analyses for guiding future high-energy neutrino searches in the KM3NeT era.

Abstract

Blazars are promising targets for neutrino astronomy, as highlighted by IceCube's identification of TXS 0506+056 as a cosmic neutrino source candidate. High-frequency-peaked BL Lacs (HBLs) stand out due to their characteristic electromagnetic high-energy emission properties, which makes them as well promising candidates for the production of high-energy neutrinos. Such neutrinos could be detected by KM3NeT/ARCA, a next-generation deep-sea Cherenkov detector under construction in the Mediterranean Sea. This contribution presents the results of a binned likelihood stacking analysis investigating high-energy neutrino emissions from a subset of HBLs. A total of 232 sources have been selected from the 3HSP catalogue and targeted in the analysis of KM3NeT/ARCA data taken with several detector configurations, specifically in the period in which from 6 to 21 detection units were deployed. The analysis is based on neutrino emission models of blazars developed using the LeHa-Paris numerical code, which simulates the spectral energy distribution of jetted active galactic nuclei.

KM3NeT/ARCA stacking search for high-energy neutrinos from blazars

TL;DR

This work targets high-energy neutrinos from HBL blazars using KM3NeT/ARCA in configurations with 6–21 DUs. It combines a physically motivated one-zone lepto-hadronic flux model (via LeHa-Paris) with a binned, two-dimensional stacking likelihood across 232 3HSP HBLs, deriving flux templates by rescaling the PKS 2155-304 best-fit flux and redshift scaling to place the spectral peak at eV. Background is estimated from scrambled data and IRFs provide the signal templates; the analysis finds no significant excess (, ) and sets 90% CL upper limits on the stacked flux, illustrating the approach's potential as KM3NeT/ARCA expands and models are refined. The results underscore the value of physically motivated population analyses for guiding future high-energy neutrino searches in the KM3NeT era.

Abstract

Blazars are promising targets for neutrino astronomy, as highlighted by IceCube's identification of TXS 0506+056 as a cosmic neutrino source candidate. High-frequency-peaked BL Lacs (HBLs) stand out due to their characteristic electromagnetic high-energy emission properties, which makes them as well promising candidates for the production of high-energy neutrinos. Such neutrinos could be detected by KM3NeT/ARCA, a next-generation deep-sea Cherenkov detector under construction in the Mediterranean Sea. This contribution presents the results of a binned likelihood stacking analysis investigating high-energy neutrino emissions from a subset of HBLs. A total of 232 sources have been selected from the 3HSP catalogue and targeted in the analysis of KM3NeT/ARCA data taken with several detector configurations, specifically in the period in which from 6 to 21 detection units were deployed. The analysis is based on neutrino emission models of blazars developed using the LeHa-Paris numerical code, which simulates the spectral energy distribution of jetted active galactic nuclei.

Paper Structure

This paper contains 12 sections, 4 equations, 4 figures.

Table of Contents

  1. Introduction
  2. Neutrinos from blazars
  3. Catalogue definition
  4. Neutrino fluxes
  5. Data sample and event selection
  6. Background and signal modeling
  7. Stacking analysis
  8. Likelihood formalism
  9. Stacking Analysis Methodology
  10. Flux uncertainty and systematics
  11. Results
  12. Conclusions

Figures (4)

  • Figure 1: Sky map in equatorial coordinates showing the selected HBLs sources from the 3HSP catalogue. A total of 232 sources satisfy the selection criteria. The Galactic Plane is indicated in red.
  • Figure 2: Expected neutrino fluxes for the 232 selected HBLs (dashed colored lines) and their stacked flux (solid black line). Both neutrino and antineutrino separation and their oscillated flavor composition at Earth are considered in the calculation.
  • Figure 3: Top 10 brightest sources, among the selected HBLs of the 3HSP catalogue, ranked by the expected neutrino yield in the KM3NeT/ARCA detector. The expected number of signal events in KM3NeT/ARCA6-21 is shown as a function of the sine of the source declination ($\delta$).
  • Figure 4: Sensitivity at 90% confidence level (solid red line) and discovery flux at $3\sigma$ significance (solid green line) for the stacked flux (solid blue), shown in the energy range where 90% of the signal is expected. The shaded light-blue region indicates the flux uncertainty. The upper limit on the central flux is indicated as a red dashed line.