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Broad Absorption Line Quasars Observed by the ROSAT PSPCRecent results from the ROSAT All-Sky Survey have shown that Broad Absorption Line (BAL) QSOs are either highly absorbed or underluminous in the soft X-ray bandpass. Here we extend this work by analyzing all known bona fide BAL QSOs observed within the inner 20 min of the ROSAT Position Sensitive Proportional Counter. This sample includes both targeted and serendipitous exposures ranging from 8 to 75 ks. Despite these deep exposures, most of the BAL QSOs are undetected and have unusually weak X-ray emission, as evidenced by large optical-to-X-ray slopes alpha(sub ox). Large values of alpha(sub ox)(approx. greater than 1.8) may prove to be a defining characteristic of BAL QSOs. We predict that samples of QSO candidates with large alpha(sub ox) will yield a higher percentage of BAL QSOs, particularly at low redshift. As a corollary, X-ray selected QSO samples should yield fewer BAL QSOs. The optical/UV emission line spectra of BAL and non-BAL QSOs are quite similar, suggesting that their intrinsic spectral energy distributions are similar as well. Absorption thus seems the likely reason for the X-ray-quiet nature of BAL QSOs. To constrain the total absorbing column of the BAL clouds, we compare our measured soft X-ray fluxes or upper limits with those expected from normal radio-quiet QSOs of comparable optical continuum magnitude and redshift. From sensitive X-ray observations, we derive column densities of approx. less than 2 x 10(exp 22)/sq cm for intrinsic cold absorbers of solar metallicity. These new results suggest columns at least an order of magnitude larger than the columns previously estimated from optical/UV spectra alone.
Document ID
19980037748
Acquisition Source
Headquarters
Document Type
Reprint (Version printed in journal)
Authors
Green, Paul J.
(Harvard-Smithsonian Center for Astrophysics Cambridge, MA United States)
Mathur, Smita
(Harvard-Smithsonian Center for Astrophysics Cambridge, MA United States)
Date Acquired
August 18, 2013
Publication Date
May 1, 1997
Publication Information
Publication: Absorbing Outflows in AGN
Publisher: American Astronomical Society
Subject Category
Astronomy
Funding Number(s)
CONTRACT_GRANT: NAS5-26555
CONTRACT_GRANT: HF-1032.01-92A
CONTRACT_GRANT: NSF INT-92-01412
CONTRACT_GRANT: NAGw-4490
Distribution Limits
Public
Copyright
Public Use Permitted.
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