Extended emission and spectral break in Cen A

Abstract

The radio galaxy Cen A has been detected all the way up to the TeV energy range. This raises the question about the dominant emission mechanisms in the high-energy domain. Spectral analysis allows us to put constraints on the possible emission processes. Here we study the hard X-ray emission, in order to distinguish between a thermal or non-thermal inverse Compton process. The hard X-ray spectrum of Cen A shows a significant cut-off at energies E C = 434 −0.10 . Extending this model to the gamma-ray range shows that a different physical component is responsible for the high-energy emission. The analysis of the SPI data provides no sign of significant emission from the radio lobes and gives a 3" upper limit of f 40−1000 keV < 1.1 × 10 −3 ph cm −2 s −1 . We find though some indication of emission near to the northern lobe of Cen A which we investigate in more detail.