The complex gamma-ray behaviour of the Radio Galaxy M87

Abstract

Context.In recent years, non-blazar Active Galactic Nuclei (AGN) such as Radio Galaxies have emerged as a highly instructive source class providing unique insights into high energy acceleration and radiation mechanisms. Aims.Here we aim at a detailed characterization of the high-energy (HE;>100 MeV) gamma-ray emission from the prominent radio galaxy M87. Methods.We analyze 8 years of Fermi-LAT data and derive the spectral energy distribution between 100 MeV and 300 GeV. We extract lightcurves and investigate the variability behaviour for the entire energy range as well as below and above 10 GeV. Results.Our analysis provides (i)evidence for HE gamma-ray flux variability and (ii)indications for a possible excess over the standard power-law model above Eb~10 GeV, similar to the earlier indications in the case of Cen A. When viewed in HE-VHE context, this is most naturally explained by an additional component dominating the highest-energy part of the spectrum. Investigation of the gamma-ray lightcurves suggests that the lower-energy (<10 GeV) component is variable on timescales of (at least) a few months. The statistics of the high energy component (>10 GeV) does not allow significant constraints on variability. We find indications, however, for spectral changes with time that support variability of the putative additional component and seem to favor jet-related scenarios for its origin capable of accommodating month-type variability. Conclusions.The current findings suggest that both the high-energy (> Eb) and the very high energy (VHE;>100 GeV) emission in M87 are compatible with originating from the same physical component. The variability behaviour at VHE then allows further constraints on the location and the nature of the second component. In particular, these considerations suggest that the VHE emission during the quiescent state originates in a similar region as during the flare.

updated version; accepted by A&A

References in corpus (14)

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• Fast variability of TeV gamma-rays from the radio galaxy M 87
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Cited by in corpus (10)

• Radio Galaxies at VHE energies
• Hadronic High-energy Emission from Magnetically Arrested Disks in Radio Galaxies
• A survey of active galaxies at TeV photon energies with the HAWC gamma-ray observatory
• Curvature in the very-high energy gamma-ray spectrum of M87
• A search for Centaurus A-like features in the spectra of Fermi-LAT detected radio galaxies
• Gap-type Particle Acceleration in the Magnetospheres of Rotating Supermassive Black Holes
• Detection of very high-energy gamma-ray emission from the radio galaxy M87 with LHAASO
• High-energy Gamma-rays from Magnetically Arrested Disks in Nearby Radio Galaxies
• A two-fluid model for black-hole accretion flows: Particle acceleration, outflows, and TeV emission
• Explaining the Origin of TeV Gamma Rays from M87 During High and Low States