Program: GN-2015A-FT-13

Broad absorption line (BAL) quasars exhibit ultraviolet absorption troughs and generally also exhibit X-ray absorption, but how those two absorption components are connected is not well understood. To improve our understanding, we are studying two intriguing populations of BAL quasars in the X-ray (ongoing Chandra observations) and the UV (ground-based spectroscopy). First is a sample of BAL quasars whose UV troughs have disappeared. Rest-frame UV spectroscopy is needed to interpret X-ray observations of such quasars, e.g., the detection of X-ray absorption without UV absorption would show that winds do not occur along all X-ray shielded lines of sight. Or, if our proposed spectroscopy reveals reappeared UV troughs at the same velocities, that would pinpoint ionization changes as the cause of UV variability. Second is a sample of BAL quasars with apparently infalling troughs reaching velocities of thousands of km/s. We may be observing gas infall to small radii, rotationally dominated outflows, or binary quasars where a wind is seen in silhouette. Our Chandra observations are testing these models by measuring any X-ray absorption from shielding gas along our line of sight, but contemporaneous rest-UV spectroscopy is needed to check whether any significant changes in UV absorption have occurred.