出版社：SISSA, Scuola Internazionale Superiore di Studi Avanzati
摘要：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 EC = 434+109 −74 keV with an underlying power law of photon index ! = 1.73±0.02. A more physical model of thermal Comptonisation (compPS) gives a plasma temperature of kTe = 206±62keV within the optically thin corona with Compton parameter y = 0.42 +0.09 −0.06 . The reflection component is significant at the 3.6" level with R = 0.12 +0.09 −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 f40−1000keV < 1.1×10−3phcm−2 s−1. We find though some indication of emission near to the northern lobe of Cen A which we investigate in more detail.
