The γ-ray spectrum of the core of Centaurus A as observed with H.E.S.S. and Fermi-LAT

• Verfasst von: Abdalla, Hassan [VerfasserIn]
• Verfasst von: Eisenacher Glawion, Dorit [VerfasserIn]
• Verfasst von: Jankowsky, Felix [VerfasserIn]
• Verfasst von: Mohamed, Mahmoud [VerfasserIn]
• Verfasst von: Quirrenbach, Andreas [VerfasserIn]
• Verfasst von: Schwemmer, Stephanie [VerfasserIn]
• Verfasst von: Wagner, Stefan [VerfasserIn]
• Titel: The γ-ray spectrum of the core of Centaurus A as observed with H.E.S.S. and Fermi-LAT
• Körperschaft: H.E.S.S. Collaboration [VerfasserIn]
• Verf.angabe: H.E.S.S. Collaboration, H. Abdalla, D. Glawion, F. Jankowsky, M. Mohamed, A. Quirrenbach, S. Schwemmer, S.J. Wagner [und weitere]
• E-Jahr: 2018
• Jahr: 19 Jul 2018
• Umfang: 10 S.
• Fussnoten: Gesehen am 07.08.2020
• Titel Quelle: Enthalten in: De.arxiv.org
• Ort Quelle: [S.l.] : Arxiv.org, 1991
• Jahr Quelle: 2018
• Band/Heft Quelle: (2018) Artikel-Nummer 1807.07375, 10 Seiten
• DOI: doi:10.1051/0004-6361/201832640
• Datenträger: Online-Ressource
• Sprache: eng
• K10plus-PPN: 158662329X

Abstract

Centaurus A (Cen A) is the nearest radio galaxy discovered as a very-high-energy (VHE; 100 GeV-100 TeV) $γ$-ray source by the High Energy Stereoscopic System (H.E.S.S.). It is a faint VHE $γ$-ray emitter, though its VHE flux exceeds both the extrapolation from early Fermi-LAT observations as well as expectations from a (misaligned) single-zone synchrotron-self Compton (SSC) description. The latter atisfactorily reproduces the emission from Cen A at lower energies up to a few GeV. New observations with H.E.S.S., comparable in exposure time to those previously reported, were performed and eight years of Fermi-LAT data were accumulated to clarify the spectral characteristics of the $γ$-ray emission from the core of Cen A. The results allow us for the first time to achieve the goal of constructing a representative, contemporaneous $γ$-ray core spectrum of Cen A over almost five orders of magnitude in energy. Advanced analysis methods, including the template fitting method, allow detection in the VHE range of the core with a statistical significance of 12$σ$ on the basis of 213 hours of total exposure time. The spectrum in the energy range of 250 GeV-6 TeV is compatible with a power-law function with a photon index $Γ=2.52\pm0.13_{\mathrm{stat}}\pm0.20_{\mathrm{sys}}$. An updated Fermi-LAT analysis provides evidence for spectral hardening by $ΔΓ\simeq0.4\pm0.1$ at $γ$-ray energies above $2.8^{+1.0}_{-0.6}$ GeV at a level of $4.0σ$. The fact that the spectrum hardens at GeV energies and extends into the VHE regime disfavour a single-zone SSC interpretation for the overall spectral energy istribution (SED) of the core and is suggestive of a new $γ$-ray emitting component connecting the high-energy emission above the break energy to the one observed at VHE energies.