The origin of the gamma-ray emission from M 87 is currently a matter of debate. This work aims to localize the very high-energy (VHE; 100 GeV – 100 TeV) gamma-ray emission from M 87 and probe a potential extended hadronic emission component in the inner Virgo Cluster. The search for a steady and extended gamma-ray signal around M 87 can constrain the cosmic-ray energy density and the pressure exerted by the cosmic rays onto the intracluster medium and allow us to investigate the role of cosmic rays in the active galactic nucleus feedback as a heating mechanism in the Virgo Cluster. The High Energy Stereoscopic System (H.E.S.S.) telescopes are sensitive to VHE gamma rays and have been used to observe M 87 since 2004. We utilized a Bayesian block analysis to identify M 87 emission states with H.E.S.S. observations from 2004 to 2021, dividing them into low, intermediate, and high states. Because of the causality argument, an extended (≳1 kpc) signal is allowed only in steady emission states. Hence, we fitted the morphology of the 120 h low-state data and find no significant gamma-ray extension. Therefore, we derive for the low state an upper limit of 58″(corresponding to ≈4.6 kpc) in the extension of a single-component morphological model described by a rotationally symmetric 2D Gaussian model at the 99.7% confidence level. Our results exclude the radio lobes (≈30 kpc) as the principal component of the VHE gamma-ray emission from the low state of M 87. The gamma-ray emission is compatible with a single emission region at the radio core of M 87. These results, with the help of two multiple-component models, constrain the maximum cosmic-ray to thermal pressure ratio to XCR, max. ≲ 0.32 and the total energy in cosmic-ray protons to UCR ≲ 5 × 1058 erg in the inner 20 kpc of the Virgo Cluster for an assumed cosmic-ray proton power-law distribution in momentum with spectral index αp = 2.1.
Constraining the cosmic-ray pressure in the inner Virgo Cluster using H.E.S.S. observations of M 87
- F. Aharonian et al. (H.E.S.S. Collaboration)
- Astronomy & Astrophysics 675, A138 (2023)
- 2023
Abstract
Auxiliary informations
Corresponding authors: Victor Barbosa Martins, Stefan Ohm, Cornelia Arcaro, Natalia Żywucka, Mathieu de Naurois.
Main paper
Figure 1
Data points – H.E.S.S. 30-day binned light curve
H.E.S.S. sky maps for M87 low state
FITS file for excess map
FITS file for significance map
Figure 2
Figure 3
Figure 4
| Spectral index | X_CR,max (magnetic confinement model) | X_CR,max (steady state model) |
|---|---|---|
| 2.1 | 0.1967 | 0.3205 |
| 2.2 | 0.2555 | 0.4164 |
| 2.3 | 0.4348 | 0.7085 |
| 2.4 | 0.8186 | 1.3354 |
| 2.5 | 1.6254 | 2.6485 |
| 2.6 | 3.3185 | 5.4072 |
Appendices
Figure A.1
Data points – H.E.S.S. 1-day binned light curve
Data points – H.E.S.S. 7-day binned light curve
Data points – H.E.S.S. 15-day binned light curve
Figure C.1
FITS file for 2D-model-LOFAR (top)
FITS file for 2D-model-LOFAR convolved with PSF (bottom)
Figure C.2
FITS file for 2D-model-steady_state (top)
FITS file for 2D-model-steady_state convolved with PSF (bottom)
Additional information
99.7% c.l. UL on the total energy in cosmic-ray protons in the inner 20 kpc
| Spectral index | E_T – magnetic confinement model (erg) | E_T – steady state model (erg) |
|---|---|---|
| 2.1 | 5.1e+58 | 5.4e+58 |
| 2.2 | 6.6e+58 | 7.0e+58 |
| 2.3 | 1.1e+59 | 1.0e+59 |
| 2.4 | 2.1e+59 | 2.2e+59 |
| 2.5 | 4.2e+59 | 4.4e+59 |
| 2.6 | 8.6e+59 | 9.1e+59 |
Gamma-ray template for the steady-state model (fine bins)
FITS file for 2D-model-steady_state_fine
H.E.S.S. PSF for the defined low state of M 87
FITS file for H.E.S.S. PSF for the defined low state of M 87
Collaboration Acknowledgement
The support of the Namibian authorities and of the University of Namibia in facilitating the construction and operation of H.E.S.S. is gratefully acknowledged, as is the support by the German Ministry for Education and Research (BMBF), the Max Planck Society, the German Research Foundation (DFG), the Helmholtz Association, the Alexander von Humboldt Foundation, the French Ministry of Higher Education, Research and Innovation, the Centre National de la Recherche Scientifique (CNRS/IN2P3 and CNRS/INSU), the Commissariat à l’Énergie atomique et aux Énergies alternatives (CEA), the U.K. Science and Technology Facilities Council (STFC), the Knut and Alice Wallenberg Foundation, the National Science Centre, Poland grant no. 2016/22/M/ST9/00382, the South African Department of Science and Technology and National Research Foundation, the University of Namibia, the National Commission on Research, Science & Technology of Namibia (NCRST), the Austrian Federal Ministry of Education, Science and Research and the Austrian Science Fund (FWF), the Australian Research Council (ARC), the Japan Society for the Promotion of Science and by the University of Amsterdam. We appreciate the excellent work of the technical support staff in Berlin, Zeuthen, Heidelberg, Palaiseau, Paris, Saclay, Tübingen and in Namibia in the construction and operation of the equipment. This work benefited from services provided by the H.E.S.S. Virtual Organisation, supported by the national resource providers of the EGI Federation.
