Constraints on neutrino emission and hadronic flux from 1LHAASO catalog $γ$-ray sources

Abstract

IceCube has detected neutrino emission from the Galactic Plane (GP) at a significance of $4.5σ$, though its origin remains uncertain. Utilizing ten years of IceCube muon-track data, we investigate potential correlations between the GP neutrinos and $γ$-ray sources in the first LHAASO catalog (1LHAASO). To avoid issues caused by spectral extrapolation, this analysis focuses on sources detected by the Water Cherenkov Detector Array (WCDA). We employ an unbinned likelihood analysis to search for neutrino emission and constrain the hadronic $γ$-ray component of these sources. Neither single-source searches nor stacking analyses reveal significant neutrino signals. The stacking analysis indicates that the 1LHAASO WCDA population contributes at most $\sim$20\% to the diffuse GP neutrino flux measured by IceCube. The total hadronic contribution to the cumulative $γ$-ray emission from all WCDA sources is constrained to be at most $\sim$$60\%$, suggesting a predominantly leptonic origin for the $γ$-ray emission from the LHAASO source population. Even accounting for unresolved sources below the detection threshold, we estimate the total neutrino flux from all discrete sources (resolved plus unresolved) reaches at most about 40\% of the observed GP neutrino flux. These results support that the bulk of the GP neutrino emission is mainly from truly diffuse processes, i.e., cosmic-ray interactions with the interstellar medium, rather than from unresolved point sources.

Figures (7)

• Figure 1: The change of the TS value from the stacking analysis as a function of the total neutrino flux of the sources in the LHAASO WCDA catalog, for different neutrino spectral indices. The green dashed line represents the result using the actual detected spectral indices reported in the LHAASO catalog, while the blue lines are the results for different assumed average spectral indices. The diffuse Galactic plane neutrino flux measured by IceCube (using the $\pi^0$ model, vertical dark blue band) IceCube:2023ame is also shown. The dashed line corresponds to ${\rm TS} = -3.84$, representing the 95% confidence level TS threshold for the case of two degrees of freedom.
• Figure 2: The 95% C.L. upper limits on the total neutrino flux from the sources in the LHAASO WCDA sample (green, blue and gray lines). The green dashed line corresponds to the result derived using the actual spectra measured by LHAASO, while the shaded bands represent the uncertainties from the LHAASO flux normalizations. The blue solid line corresponds to the upper limits obtained by assuming an average spectrum of a smoothly broken power-law with a break at 40 TeV. The gray lines assume power-law average spectra with different spectral indices. These constraints are compared with the diffuse neutrino flux observed by IceCube from the Galactic plane IceCube:2023ame, adopting the $\pi^0$ model (light blue), the $\text{KRA}^{5}_{\gamma}$ model (orange), and the $\text{KRA}^{50}_{\gamma}$ model (dark blue). Our results indicate the sources in the LHAASO catalog cannot account for all of the observed Galactic plane neutrino flux, contributing at most $\sim$20% of the GP neutrinos compared to the $\pi^0$ result.
• Figure 3: Similar to Fig. \ref{['fig:wcda']}, but for the LHAASO KM2A sources.
• Figure 4: The signal PDF for the $\pi^0$ map after convolution.
• Figure 5: The signal PDF after scrambling.