Search for X--ray spectral features in two BL Lac Objects

We propose 20 ks XMM observations on each of the two Xray bright BL Lac objects Mkn 180 and 1ES1517+656. Our primary aim is to study the strong soft Xray absorption feaures that are sometimes seen in BL Lac objects (such as PKS 2155304 and others). Our main scientific goals are (1) to begin determining how generic these features are in BL Lacs; and (2) to study these features in sufficient detail to determine their origin. Other benefits may also accrue, such as detecting intervening absorption, or providing a new way to measure BL Lac object redshifts. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]