Title: A Study of the ADAF Phenomenon in nearby AGN
Proposal ID: 0120050
Subject category: Extragalactic Object
Principal investigator: Dean
Institute: University of Southampton
Abstract
We propose to compare and contrast the broadband soft gamma-ray spectra of three carefully chosen nearby
active galaxies. These objects offer fascinating astrophysics in the context of post middle-aged AGN studies
on a number of levels. They are all radiating at a level considerably below the Eddington limit expected
from their known central black hole masses; this in itself suggest that these sources may be subject to the
ADAF mechanism. The extensive broadband coverage of INTEGRAL enables both the direct emissions from the
central engine to be measured at the same time that the local absorption and scattering effects are
assessed. By assessing the slope of the high energy spectrum we can confirm (or otherwise) the presence of
an ADAF in these objects and hence understand the physical reason behind their sub-Eddington luminosities.
All three have different formal AGN classifications but appear to exhibit many fundamentally similar
characteristics as far as the central engine is concerned. The incisive INTEGRAL probe can thus bring the
similarities and/or differences into sharper focus in a new waveband. These AGN are undoubtedly less active
than they were in their youth. The study also provides an opportunity to investigate the AGN-"normal galaxy"
connection and assess the contribution of such objects to the Cosmic Diffuse Background. These examples are
nearby. Thus despite the intrinsically low luminosity of the ADAF process, NGC 4258, NGC 5194 and NGC 1052
are bright enough to be easily detectable by JEMX, IBIS-ISGRI over the desired energy range. In fact BATSE
and BeppoSAX have already detected them in the 20-100 keV band. We request a 100 Ks exposure for each
individual source, as this will allow us to reach ~10-20 sigma in the20-200 keV band; this is sufficient to
fulfil the scientific goals of the present proposal. We propose NGC4258 as our priority target, M51and
NGC1052 as our second and third target choice respectively