Exceptional X-ray Weak Quasars and their Implications for Accretion Flows, Broad Line Regions, and Winds
Presented by Niel Brandt
Pennsylvania State University
Thursday, May 28, 2015
4:00 P.M. in 169-336
Actively accreting supermassive black holes are found, nearly universally, to create luminous X-ray emission, and this point underlies the utility of X-ray surveys for finding active galactic nuclei throughout the Universe. However, there are apparent X-ray weak exceptions to this rule that are now providing novel insights, including weak-line quasars (WLQs) and especially analogs of the extreme WLQ, PHL 1811. We have been systematically studying such X-ray weak quasars with Chandra and near-infrared spectroscopy, and I will report results on their remarkable properties and describe implications for models of the accretion disk/corona, emission-line formation, and quasar winds. We have found evidence that many of these quasars may have geometrically thick inner accretion disks, likely due to high accretion rates, that shield the high-ionization broad line region from the relevant ionizing continuum. This model can explain, in a simple and unified manner, their weak lines and diverse X-ray properties. Such shielding may, more generally, play a role in shaping the broad distributions of quasar emission-line equivalent widths and blueshifts. Furthermore, I will report NuSTAR observations indicating that a significant fraction of BAL quasars are intrinsically X-ray weak, thereby promoting strong wind driving. I will end by discussing some promising ongoing studies that are extending these ideas.
JPL Contact: Charles Lawrence (4-5307)
About the Speaker
Niel Brandt is the Verne M. Willaman Professor of Astronomy and Astrophysics at Penn State.