An XMM-Newton Set of Long Observations of NGC 1365: Probing AGN Structure and General Relativity
Abstract
Our project is mainly based on an approved XMM-Newton large program consisting of a 500 ks monitoring campaign of the obscured AGN in NGC 1365, a source which stands as the Rosetta stone among Seyfert galaxies, for its exceptional set of observational properties allowing unique and precise tests of AGN structure and general relativistic effects. A new method developed by our group, based on time-resolved X-ray spectroscopy, revealed that X-ray absorption variability is common in Active Galactic Nuclei (AGN): the gas clouds orbiting around the supermassive black hole quite often cover the X-ray source, with typical occultation times from a few hours to days. Our early work on a few selected targets demonstrates that through these AGN eclipses we have the chance of making some of the most important and long-sought measurements in black hole physics: 1) occultation times provide a direct estimate of the size of the X-ray source. This allows to check whether this emission truly originates from a few gravitational radii from the black hole, thus setting a direct, observational limit of the black hole size; 2) X-raying the obscuring clouds allows for the first time an observational (not model-based) measurement of the physical and geometrical properties of the clouds, a key step forward in order to understand the AGN line emission region; 3) X-ray occultations may provide a direct, decisive check of general relativity (GR) effects in X-ray spectra of AGNs. In particular, an X-ray eclipse allows to perform an accretion disk tomography experiment: since the relativistic effect on the line strongly depends on the disk element emitting the line, we expect peculiar profile changes during eclipses. The detection of these changes would be an unambiguous proof of GR effects. In this context, NGC 1365 is a truly unique source, due to the frequency of appearance of the occultations: so far, in several past observations with various X-ray observatories, eclipses with durations of 10-20 hours have always been detected. Our project consists of a complete analysis of the newly awarded data (four 130 ks long observations), which will be by far the longest and highest quality X-ray observations available for this source, and for a Seyfert 2 at large. Beyond addressing all the points described above with unprecedented detail, we will also investigate the other peculiar spectral properties of NGC 1365: a highly ionized outflow (the one detected with the highest S/N so far), a strong diffuse thermal emission, an active host galaxy, including two of the most powerful known ULXs. Finally, simultaneous NuSTAR observations are scheduled for all the four XMM-Newton observations. This will add to our analysis the diagnostic power of a complete 0.5-100 keV coverage.
- Publication:
-
NASA ADAP Proposal
- Pub Date:
- 2012
- Bibcode:
- 2012adap.prop...62R