NuSTAR Hard X-ray Spectroscopy as a Probe of AGN Structure

Mislav Balokovic (Caltech) - December 5, 2016 at 12:10 pm

The Nuclear Spectroscopic Telescope Array (NuSTAR) has enabled studies of the local active galactic nuclei (AGN) to extend into the hard X-ray band, up to 79 keV, with unprecedented spatial resolution and sensitivity. As a part of its extragalactic program, NuSTAR is surveying the nearby population of AGN detected at hard X-ray energies by the Swift Burst Alert Telescope (Swift/BAT), selecting even the most obscured local AGN. I will highlight some of the results based on broadband X-ray spectroscopy of individual targets and present my work on the large representative sample of more than a hundred nearby obscured AGN, which constitutes the largest available atlas of hard X-ray spectra of obscured AGN to date. The high quality of the data allows us to probe the details of AGN structures such as the jet, the X-ray-emitting corona and the toroidal obscurer in the under-explored spectral window above 10 keV. I will present both phenomenological results important for synthesis models of the cosmic X-ray background, and a novel, independent approach for constraining the geometry of the gas surrounding the supermassive black hole (including the accretion disk, the broad-line region, and the torus) from the hard X-ray band. I will discuss how what we learned from this survey of local AGN relates to deeper high-redshift X-ray surveys and AGN structure probes at other wavelengths. Fully harnessing the power of high-quality data in the hard X-ray window and the high energy resolution of the X-ray calorimeters planned for the near future will require a new level of detail in theoretical spectral modeling, which I will present as the necessary next step toward better understanding of the structures surrounding supermassive black holes.

The seminar will be held in 131A Campbell Hall.


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