Speaker
Description
Radio-quiet active galactic nuclei (AGNs) have recently emerged as a potential population of high-energy gamma-ray emitters. Using 15 years of Fermi-LAT observations, we previously reported a significant stacked gamma-ray signal from a sample of nearby, hard-X-ray-bright radio-quiet AGNs, revealing their average spectral energy distribution (SED) up to hundreds of GeV. However, their emission at TeV energies remains largely unexplored, leaving the high-energy behavior of the gamma-ray spectrum and the maximum energy of accelerated particles poorly constrained.
In this work, we extend the study of this radio-quiet AGN population to the TeV regime using LHAASO observations. We perform a stacking analysis of the LHAASO data and constrain the characteristic gamma-ray flux and spectral shape at TeV energies. In the $1$-$20\,\mathrm{TeV}$ band, the combined likelihood shows a moderate excess with a maximum test statistic of $\mathrm{TS}\simeq 6.5$. The corresponding characteristic luminosity is $L_{1\text{-}20\,\mathrm{TeV}}\simeq 4.8\times10^{39}\,\mathrm{erg\,s^{-1}}$. Although the current significance is insufficient to claim a detection, the LHAASO measurement provides a new constraint on the average TeV emission of radio-quiet AGNs.
By combining the LHAASO constraints with the previously measured Fermi-LAT spectrum, we construct a broadband GeV-TeV SED for radio-quiet AGNs. The results probe the suppression of their gamma-ray emission beyond the Fermi-LAT energy range and provide new constraints on the high-energy cutoff and the maximum energies of non-thermal particles.
