Longtime Monitoring of TeV Radio Galaxies with HAWC

2025/06/19 by Alfaro, R., Alvarez, C., Anita-Rangel, E. +85 · 1 citation
Physics and Astronomy · #Astrophysics and Cosmic Phenomena #Dark Matter and Cosmic Phenomena #FOS: Physical sciences #High Energy Astrophysical Phenomena (astro-ph.HE) #Particle physics theoretical and experimental studies

paper · pdf · doi:10.48550/arxiv.2506.16031

openalex publication_date 2025/06/19 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28

Abstract

We present the monitoring of the TeV-emitting radio galaxies M87, NGC~1275, 3C~264, and IC~310 with the High Altitude Water Cherenkov Observatory (HAWC) over a period of approximately 7.5 years. The analysis includes light curves at daily, weekly and monthly time scales for the four sources. We report the detection of gamma-ray emission from M87 with a significance exceeding 5σ. Due to its significant detection, this work reports the integrated TeV spectrum of M87 from the longest temporal coverage up to date. The source is well described as a point-like source modeled by a power law spectrum with spectral index α= 2.53±0.29 and a flux of (7.09± 1.24)×10^-13 \rmcm^-2 s^-1 TeV^-1 at 1 \rmTeV. The maximum energy of the detected emission in M87, at 1σ confidence level (C.L.), reaches 26.5 TeV. HAWC's observation of M87 reveals a low flux spectrum for the longest observation to date of this radio galaxy. 3C~264 is marginally detected with a significance slightly below 4σ, while NGC~1275 and IC~310 are not detected. The weekly light curves show an increased number of fluxes above 2σ for M87 starting in 2019, and for 3C~264 starting in 2018, which can be interpreted as the moment for which these sources start to exhibit an enhanced steady TeV emission. Overall, in the four radio galaxies, the cumulative significance over time indicates a behavior that resembles that of a gamma-ray variable active galaxy, such as the blazar Markarian 421. This supports the importance of monitoring radio galaxies to identify periods of higher activity and flares, enabling further multi-messenger studies.

Citations

• Detection of very high-energy gamma-ray emission from the radio galaxy M87 with LHAASO
• Performance of the HAWC Observatory and TeV Gamma-Ray Measurements of the Crab Nebula with Improved Extensive Air Shower Reconstruction Algorithms
• Broadband multi-wavelength properties of M87 during the 2018 EHT campaign including a very high energy flaring episode
• Long-term monitoring of the radio-galaxy M87 in gamma-rays: joint analysis of MAGIC, VERITAS and Fermi-LAT data
• Study of the Very High Energy emission of M87 through its broadband spectral energy distribution
• Morphological transition of the compact radio lobe in 3C84 via the strong jet-cloud collision
• The VLBA Extragalactic Proper Motion Catalog and a Measurement of the Secular Aberration Drift
• Highlights from the VERITAS AGN Observation Program
• The major upgrade of the MAGIC telescopes, Part II: A performance study using observations of the Crab Nebula

Cited by

• Explaining the Origin of TeV Gamma Rays from M87 During High and Low States

Related

• Monitoring radio galaxies at TeV energies with HAWC
• Observation of radio galaxies with HAWC
• A survey of Active Galaxies with the HAWC Gamma-ray Observatory
• Monitoring TeV blazars with HAWC
• A first joint M87 campaign in 2008 from radio to TeV gamma-rays