Hadronic Clues in Quasars Caught by Fermi-LAT

TL;DR

The paper investigates whether hadronic processes can account for the high-energy emission observed in Fermi-LAT–identified quasars by coupling leptonic and hadronic components within a one-zone jet model and comparing to IceCube neutrino data. It conducts a systematic spatial and temporal cross-correlation between IceCube track-like neutrinos and 4LAC FSRQs, quantifying association significance with serendipity probabilities derived from Monte Carlo trials. The authors fit archival multiwavelength SEDs with a lepto-hadronic model using MCMC, finding that hadronic contributions are required to reproduce the SEDs but do not yield a sufficiently large neutrino flux to account for IceCube events. They conclude the jets are particle-dominated, highlight IR–optical excesses likely from disk emission, and emphasize the need for simultaneous multiwavelength campaigns to robustly constrain hadronic contributions and neutrino yields in blazars.

Abstract

This work explores whether hadronic processes could be responsible for the high-energy emission seen in quasars identified by the Large Area Telescope (LAT) instrument aboard the Fermi satellite. In contrast to purely leptonic models, this work investigates whether hadronic mechanisms can explain the observed gamma-ray spectra by analyzing the spectral energy distributions (SEDs) of a chosen sample of FSRQs (Flat-Spectrum Radio Quasars). By incorporating both hadronic and leptonic components into their multi-wavelength modeling, we evaluate the model's feasibility to simultaneously describe the data collected by Fermi-LAT and neutrinos detected by IceCube. According to the results, a hadronic contribution would be required to explain the SED of quasars detected by Fermi-LAT. However, their contribution to the neutrino flux detected by IceCube remains understated.

Figures (21)

• Figure 1: Serendipity probability for each spatial correlation found. As it can be appreciated, the match rate remains low ($\sim1\%$) for all the sources. The black line shows the probability obtained and the gray filled area denotes 1$\sigma$ of the mean value.
• Figure 2: Photon rate detected by Fermi-LAT from 4FGL J2226.8+0051 over 15 years of data acquisition. The vertical dashed line denotes the time of detection of the neutrino by IceCube. In other hand, the vertical shaded region represents the area in which is detected a flare period accord on Hop criteria.
• Figure 3: The same as Figure \ref{['fig:LC_IC110807A']} but for 4FGL J1744.2-0353 and the detection of the neutrino IC110930A.
• Figure 4: The same as Figure \ref{['fig:LC_IC110807A']} but for 4FGL J1310.5+3221 at top. At bottom 4FGL J1311.0+3233. From the two cases with the detection of the neutrino IC120515A.
• Figure 5: The same as Figure \ref{['fig:LC_IC110807A']} but for 4FGL J1204.8+0407 and the detection of the neutrino IC120916A.