出版社：SISSA, Scuola Internazionale Superiore di Studi Avanzati
摘要：We present some results of the INTEGRAL observation campaign of the bright Seyfert galaxy NGC 4151. The INTEGRAL observations cover 7 years, for a total of more than 1.5Ms effective exposure with ISGRI over 31 revolutions. We determine the physical parameters of the plasma responsible for the medium and hard X-ray emission (> 3 keV). Significant variability in plasma temperature and optical depth are found, but the Compton y parameter is practically constant, indicating a stable geometry. The plasma is found to be photon-starved, with a Comptonized flux about 15 times the seed-photon flux. We measure the reflected fraction and conclude that both a distant and a nearby reflector are needed, with similar reflection parameters, which we interpret as originating from the torus and from the accretion disk, respectively. The small disk reflection parameter, RDisk '0:27, is an evidence for a truncated accretion disk, turning into a hot, radiatively inefficient accretion flow at a radius determined from the soft-photon seed emission to be 18RG.
