A Chandra Survey of Broad Absorption Line Quasars

Abstract

We have carried out a survey with the Chandra X-ray Observatory of a sample of 10 optically bright broad absorption line (BAL) QSOs. Eight out of ten sources are detected. The 6 brightest X-ray sources have only high ionization BALs (hiBALs), while the 4 faintest all show low ionization BALs (loBALs). We perform a combined spectral fit for hiBAL QSOs to determine the mean spectral parameters of this sample. We derive an underlying best-fit power-law slope Gamma=1.8+/-0.35, consistent with the mean slope for radio-quiet quasars from ASCA, but BALQSOs require a (restframe) absorbing column of 6.5e22, with a partial covering fraction of 80%. Removing the absorption component from our best-fit spectral model yields a range of alphaOX from 1.55 to 2.28. All 6 hiBAL QSOs have de-absorbed X-ray emission consistent with non-BAL QSOs of similar luminosity. The spectral energy distributions of the hiBAL QSOs - both the underlying power-law slope and alphaOX provide the first conclusive evidence that BALQSOs have appeared to be X-ray weak because of intrinsic absorption, and that their underlying emission is consistent with non-BAL QSOs. By contrast, removal of the best-fit absorption column detected in the hiBAL QSOs still leaves the 4 loBAL QSOs as unusually X-ray faint for their optical luminosities.

12 pages, Latex, emulateapj style, including 3 tables and 3 figures. Accepted May 15, 2001 for publication in ApJ Main Journal. See also http://hea-www.harvard.edu/~pgreen/Papers.html Replaced May 21 since 2 lines were missing from Table 2