The Pennsylvania State University The Graduate School Department of Astronomy and Astrophysics THE VIEW THROUGH THE WIND: X-RAY OBSERVATIONS OF BROAD ABSORPTION LINE QUASI-STELLAR OBJECTS A Thesis in Astronomy and Astrophysics by Sarah Connoran Gallagher c 2002 Sarah Connoran Gallagher Submitted in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy May 2002 We approve the thesis of Sarah Connoran Gallagher. Date of Signature W. Nielsen Brandt Associate Professor of Astronomy and Astrophysics Thesis Adviser Chair of Committee Jane C. Charlton Associate Professor of Astronomy and Astrophysics Michael C. Eracleous Assistant Professor of Astronomy and Astrophysics L. Samuel Finn Associate Professor of Physics Gordon P. Garmire Evan Pugh Professor of Astronomy and Astrophysics Steinn Sigurdsson Assistant Professor of Astronomy and Astrophysics Peter I. M´esz´aros Professor of Astronomy and Astrophysics Head of the Department of Astronomy and Astrophysics iii Abstract The 2{10 keV bandpasses and unprecedented sensitivity of modern X-ray obser- vatories have enabled new insights into the immediate environments of Broad Absorp- tion Line (BAL) QSOs. BAL QSOs, approximately 10% of the QSO population, exhibit deep, broad absorption lines from high ionization ultraviolet resonance transitions. These blueshifted absorption features are understood to arise along lines of sight which travel through radiatively driven winds with terminal velocities reaching 0.1{0:3c. These en- ergetic outflows are an important component of QSO environments; mass ejection is apparently fundamentally linked to the process of active mass accretion onto super- massive black holes. X-rays, generated in the innermost regions surrounding accreting black holes, travel through the nuclear environments to the observer. X-ray studies of BAL QSOs thus offer a privileged view through the wind. In this thesis, I present the results from X-ray surveys of BAL QSOs. This work includes both spectroscopic and exploratory X-ray observations designed to characterize the X-ray properties of specific objects as well as the population as a whole. Before this project, BAL QSOs were known to be X-ray weak relative to normal QSOs, however, the cause for this faintness had not been demonstrated. In general, I find that X-ray weak- ness in BAL QSOs results from intrinsic absorption of a typical QSO X-ray continuum. Fitting X-ray spectra with simple absorption models results in intrinsic column densities 22 2 ranging from (1{50) 10 cm− . Even at the spectral resolution currently available for × such observations, there is significant evidence for complexity in the absorber, perhaps arising from ionized gas with velocity structure that may partially cover the direct con- tinuum. From the X-ray continua above 5 keV, the X-ray to ultraviolet flux ratios ∼ are found to be consistent with normal QSOs, indicating that the spectral energy dis- tributions of BAL QSOs are not anomalous. For those BAL QSOs exhibiting BALs in low-ionization lines (e.g., Mg ii), the situation is qualitatively different. The direct line of sight to the primary X-ray continuum appears to be completely blocked by Compton- thick absorption. In this situation, only indirect X-rays, either scattered or reflected, are able to reach the observer. In the future, deeper observations of the brightest BAL QSOs as well as expanded exploratory surveys will offer additional insight into the state and location of the X-ray absorbers. Higher spectral resolution will clarify the physical state of the X-ray absorber as well as elucidate the relationship between the ultraviolet and X-ray absorbing gas. This information is essential for attaining the ultimate goal of constraining the mass outflow rate of luminous QSOs. iv Table of Contents List of Tables : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : vii List of Figures : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : viii Acknowledgments : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : ix Chapter 1. Introduction : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 1 1.1 Active Galactic Nuclei . 1 1.1.1 The Standard Model . 1 1.1.2 Progress Towards Unification . 1 1.1.3 Radio-Loud/Radio-Quiet AGN . 2 1.2 Broad Absorption Line QSOs . 3 1.2.1 Continuum and Spectral Energy Distribution . 3 1.2.2 X-ray Properties (circa 1997) . 4 1.2.3 Broad Absorption Lines . 5 1.2.4 Polarization . 6 1.2.5 Variability . 6 1.2.6 Observational Subclasses . 7 1.2.7 Theoretical Models for BAL QSOs . 9 1.3 Motivation for this Project . 10 1.3.1 The Value of X-ray Studies . 11 1.4 Outline of the Thesis . 12 1.4.1 Chapter 2: Exploratory ASCA Observations of BAL QSOs . 12 1.4.2 Chapter 3: Heavy Absorption in Soft X-ray Weak AGN . 13 1.4.3 Chapter 4: Markarian 231: A Prototypical Low-Ionization BAL QSO? . 13 1.4.4 Chapter 5: X-ray Spectroscopy of QSOs with Broad Ultravi- olet Absorption . 14 1.4.5 Chapter 6: First Results from an Exploratory Chandra Survey of Large Bright Quasar Survey BAL QSOs . 14 1.4.6 Conclusions . 14 Chapter 2. Exploratory ASCA Observations of Broad Absorption Line Quasi-Stellar Objects : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 16 2.1 Introduction . 16 2.2 Observations and Data Analysis . 19 2.2.1 Observation Details and Data Reduction . 19 2.2.2 Image Analyses and Count Rate Constraints . 19 2.2.3 Column Density Constraints . 20 2.3 Notes on Individual Observations . 25 2.4 Conclusions and Future Prospects . 27 v Chapter 3. Heavy X-ray Absorption in Soft X-ray Weak Active Galactic Nuclei 29 3.1 Introduction . 29 3.2 Observations and Data Analysis . 32 3.2.1 PG 1011{040 . 34 3.2.2 PG 1535+547 (Mrk 486) . 37 3.2.3 PG 2112+059 . 40 3.3 Discussion and Conclusions . 43 3.3.1 PG 1011{040 . 43 3.3.2 PG 1535+547 (Mrk 486) . 43 3.3.3 PG 2112+059 . 44 3.3.4 X-ray Absorption as the Primary Cause of Soft X-ray Weakness 46 3.3.5 X-ray and UV Variability . 47 3.3.6 Soft X-ray Weak AGN and the X-ray Background . 47 Chapter 4. Markarian 231, a Prototypical Low-Ionization BAL QSO? : : : : : : 50 4.1 Introduction . 50 4.2 Observations and Data Reduction . 52 4.3 Image Analysis . 53 4.3.1 Nucleus and Extended Emission . 53 4.3.2 Non-Nuclear Point Sources . 54 4.4 Variability Analysis . 55 4.5 Spectral Analysis . 56 4.5.1 Nucleus . 56 4.5.1.1 Spectrum Extraction . 56 4.5.1.2 Basic Spectral Modeling . 58 4.5.1.3 Reflection-Dominated Spectrum and Iron Line . 59 4.5.1.4 Alternate Model . 61 4.5.1.5 A Jet Contribution to the X-ray Flux? . 61 4.5.1.6 Spectral Checks . 62 4.5.2 Extended Galaxy Emission . 63 4.6 Discussion . 76 4.6.1 Mrk 231 as a Broad Absorption Line QSO . 76 4.6.1.1 Spectroscopic Classification . 76 4.6.1.2 X-ray Variability and Spectral Results . 77 4.6.2 Mrk 231 as a Starburst Galaxy . 80 4.7 Future Work . 80 Chapter 5. X-ray Spectroscopy of QSOs with Broad Ultraviolet Absorption Lines 83 5.1 Introduction . 83 5.2 Sample Data . 84 5.3 Results . 86 5.3.1 Normal Underlying QSO Continua . 86 5.3.2 Complex Absorption . 86 5.3.2.1 H 1413+117 . 87 5.4 Discussion . 88 vi 5.5 Future Work . 88 Chapter 6. First Results from an Exploratory Chandra Survey of Large Bright Quasar Survey Broad Absorption Line QSOs : : : : : : : : : : : : : 92 6.1 Introduction . 92 6.2 Observations and X-ray Data Analysis . 93 6.3 Testing for Significant Correlations . 96 6.4 Discussion . 100 6.5 Future Work . 101 Chapter 7. Conclusions : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 106 7.1 Plans for the Future . 106 References : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : : 108 vii List of Tables 2.1 BAL QSO General Information and Observing Log . 18 a 3 1 2.2 ASCA Detector Count Rates (10− photons s− ) . 21 2.3 Limits on Intrinsic Absorptiona . 22 3.1 General Information and Observing Log . 31 3.2 Observed ASCA Parameters . 35 3.3 Parameters of Model Fits to the ASCA Data . 38 4.1 Counts, Fluxes, and Luminosities . 57 4.2 Parameters for Model Fits to the Chandra Data for Mrk 231a . 74 4.2 Parameters for Model Fits to the Chandra Data for Mrk 231a . 75 5.1 Basic Properties of QSOs with Broad Ultraviolet Absorption Lines . 85 6.1 Basic Properties and Observation Log . 94 6.2 X-ray Properties . 97 6.3 Results from Bivariate Statistical Testsa . 98 viii List of Figures 1.1 Ultraviolet spectrum of PHL 5200, the first BAL QSO discovered . 15 1.2 X-ray absorption by neutral gas of a QSO continuum . 15 2.1 Column density lower limits for PG 0043+039: αox . 24 2.2 Column density lower limits for PG 0043+039: αix . 25 3.1 Hubble Space Telescope ultraviolet spectrum of PG 2112+059 . 33 3.2 X-ray images of soft X-ray weak AGN . 34 3.3 ASCA spectra of PG 1011{040 . 36 3.4 ASCA spectra of PG 1535+547 . 39 3.5 Confidence contours: PG 1535+547 . 40 3.6 ASCA spectra of PG 2112+059 . 41 3.7 Confidence contours: PG 2112+059 . 42 3.8 Spectral energy distributions . 48 3.9 Rest-frame C iv absorption EW versus αox . ..