JPL Home NASA Home Caltech Home
Follow this link to skip to the main content
NASA Logo - Jet Propulsion Laboratory   + View the NASA Portal
Search JPL
JPL Home Earth Solar System Stars & Galaxies Technology
Science Visitor and Colloquium Program
Information for Visitors
Astrophysics Colloquium

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.

SVCP Astrophysics

Privacy / Copyrights
  NASA Home Page
Site Manager:

CL 08-3220