出版社：SISSA, Scuola Internazionale Superiore di Studi Avanzati
摘要：Compton-thick AGN are detected in hard X-ray surveys, but their space density is significantly lower than expected. In order to test the possibility that the Compton-thick AGN population would emerge at lower fluxes, we performed follow-up observations of candidate sources detected in a very deep INTEGRAL survey. From the obtained hard X-ray mosaic and from Chandra followup and XMM-Newton observations, we find five objects with quite hard spectra, pointing to the possibility that they could be highly absorbed. We present the results for three of these objects for which we obtained optical spectra. The reflection-dominated interpretation of their spectra is not convincing, in particular because of the absence of strong iron features. Optical classification and absence of iron features point to the possibility that these objects are LINER. However the photon index is, in each case, too hard to support this interpretation. In NGC 4224, it is of 1.2 and compatible with Fanaroff-Riley type I galaxies, or even a FSRQ (Flat Spectrum Radio Quasar). ESO 575-G059 and LEDA 104441 have still harder spectral indices, respectively of 0.3 and 0.2, which remain extremely puzzling.
