Inverse compton scattering of starlight in the kiloparsec-scale jet in centaurus a

The origin of excess tev γ-ray emission

K. Tanada, Jun Kataoka, Y. Inoue

Research output: Contribution to journalArticle

Abstract

Centaurus A (Cen A) is the nearest active radio galaxy, which has kiloparsec-scale jets and giant lobes detected by various instruments in radio and X-ray frequency ranges. The Fermi-Large Area Telescope and High Energy Stereoscopic System (HESS) confirmed that Cen A is a very high-energy (VHE; >0.1 TeV) γ-ray emitter with a known spectral softening in the energy range from a few GeV to TeV. In this work, we consider a synchrotron self-Compton model in the nucleus for the broadband spectrum below the break energy and an external Compton model in kiloparsec-scale jets for the γ-ray excess. Our results show that the observed γ-ray excess can be suitably described by the inverse Compton scattering of the starlight photons in the kiloparsec-scale jets, which is consistent with the recent tentative report by HESS on the spatial extension of the TeV emission along the jets. Considering the spectral fitting results, the excess can only be seen in Cen A, which is probably due to two factors: (1) the host galaxy is approximately 50 times more luminous than other typical radio galaxies and (2) the core γ-ray spectrum quickly decays above a few MeV due to the low maximum electron Lorentz factor of γ c = 2.8 103 resulting from the large magnetic field of 3.8 G in the core. By the comparison with other γ-ray detected radio galaxies, we found that the magnetic field strength of relativistic jets scales with the distance from the central black holes d with B(d) ∝ d -0.88 0.14.

Original languageEnglish
Article number139
JournalAstrophysical Journal
Volume878
Issue number2
DOIs
Publication statusPublished - 2019 Jun 20

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rays
scattering
radio galaxies
radio
energy
magnetic field
active galaxies
softening
magnetic fields
lobes
field strength
synchrotrons
emitters
frequency ranges
telescopes
galaxies
broadband
electron
nuclei
photons

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

Cite this

Inverse compton scattering of starlight in the kiloparsec-scale jet in centaurus a : The origin of excess tev γ-ray emission. / Tanada, K.; Kataoka, Jun; Inoue, Y.

In: Astrophysical Journal, Vol. 878, No. 2, 139, 20.06.2019.

Research output: Contribution to journalArticle

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