Title: Probing the Bare Seyfert 1 Nucleus and its Local Environment


Proposal ID: 0120077
Subject category: Extragalactic Object
Principal investigator: Dean
Institute: University of Southampton

Abstract

We propose to compare and contrast the broad band gamma-ray spectrum of two carefully chosen galaxies with INTEGRAL, MCG-2-58-22 and NGC3516, with a view to obtaining a better understanding of the intrinsic high-energy radiation from the central engine of Seyfert 1 galaxies. Both objects exhibit the hallmarks of a bare Seyfert nucleus, i.e. a nucleus without spectral complexity. MCG-2-58-22 belongs to the Piccinotti sample of galaxies and is bright enough to be easily detectabed by JEMX, IBIS-ISGRI and SPI. BATSE and OSSE have in fact detected MCG-2-58-22 at high energies at a flux level of ~10^-11 erg cm-2 s-1 in the 20-100 keV. Combining measurements from IBIS and SPI we expect 28 sigma in the 20-500 keV band from an INTEGRAL observation of MCG-2-58-22. We choose MCG-2-58-22 as our prime target because previous X-ray observations indicate that this source is the best-known candidate for a bare Seyfert 1 nucleus. Furthermore the source spectrum is flatter than the canonical 1.9, indicating that a distribution of power law indices in Seyfert galaxies is possible. NGC 3516 exhibits the characteristics of a bare Seyfert 1 nucleus that intermittently suffers the effects of transient absorption. NGC3516 is likewise detectable by JEMX and IBIS-ISGRI and also by SPI when not in its lowest state. Combining measurements from IBIS and SPI we expect 50 sigma in the 20-500 keV band from an INTEGRAL observation of NGC 3516. Due to its variable nature, we wish to observe NGC 3516 on two separate occasions. Comparing and contrasting the three measurements allows (1) testing and constraining X-ray production models for an unobscured central Seyfert 1 engine. (2) Evaluation of the effect of nearby clouds on this emission, and (3) to better define the framework of the unified theory by assessing what a "bare active nucleus" and its local environment should look like.