Accession Number:

AD1100035

Title:

The gamma-Ray Spectrum of the Core of Centaurus A as Observed with H.E.S.S. and Fermi-LAT

Descriptive Note:

Journal Article - Open Access

Corporate Author:

NAVAL RESEARCH LAB WASHINGTON DC WASHINGTON United States

Report Date:

2018-07-05

Pagination or Media Count:

10.0

Abstract:

Centaurus A Cen A is the nearest radio galaxy discovered as a very-high-energy VHE 100 GeV-100 TeV gamma-ray source by the High Energy Stereoscopic System H.E.S.S.. It is a faint VHE gamma-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 satisfactorily 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 gamma-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 gamma-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 sigma on the basis of 213 hours of total exposure time. The spectrum in the energy range of 250 GeV6 TeV is compatible with a power-law function with a photon index Gamma 252 or- 013stat or- 020sys. An updated Fermi-LAT analysis provides evidence for spectral hardening by Delta gamma approx. 04 01 at gamma-ray energies above 2810-06 GeV at a level of 40. 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 distribution SED of the core and is suggestive of a new gamma-ray emitting component connecting the high-energy emission above the break energy to the one observed at VHE energies. The absence of significant variability at both GeV and TeV energies does not yet allow disentanglement of the physical nature of this component, though a jet-related origin is possible and a simple

Subject Categories:

  • Astrophysics
  • Nuclear Physics and Elementary Particle Physics

Distribution Statement:

APPROVED FOR PUBLIC RELEASE