Results for "Michael Eracleous"

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Active Galaxies With Double-Peaked Emission Lines and What They Imply About the "Broad-Line Region"Oct 22 2003I review the distinguishing observational characteristics of active galaxies with double-peaked emission lines and their implications for the nature of the line-emitting region. Since double-peaked lines most likely originate in the outer parts of the ... More
Likelihood for Detection of Sub-parsec Supermassive Black Hole Binaries in Spectroscopic SurveysMar 06 2018Jun 07 2018Motivated by observational searches for sub-parsec supermassive black hole binaries (SBHBs) we develop a modular analytic model to determine the likelihood for detection of SBHBs by ongoing spectroscopic surveys. The model combines the parametrized rate ... More
Variability of Mini-BAL and BAL Outflows in QuasarsMar 17 2012We report the results of several programs to study the variability of high-velocity (up to 0.2c) mini-"broad absorption lines" (mini-BALs) and BALs in quasar spectra, and thus to better characterize the structural and physical properties of these outflows. ... More
Probing Intermediate Mass Black Holes With Optical Emission Lines from Tidally Disrupted White DwarfsOct 28 2010We calculate the emission line spectrum produced by the debris released when a white dwarf (WD) is tidally disrupted by an intermediate-mass black hole (IMBH; $M\sim 10^{2}-10^{5}\msun$) and we explore the possibility of using the emission lines to identify ... More
Spectroscopic Observations of the Outflowing Wind in the Lensed Quasar SDSS J1001+5027Jan 12 2018We performed spectroscopic observations of the small-separation lensed quasar SDSS J1001+5027, whose images have an angular separation $\theta \sim 2.^{\!\!\prime\prime}86$, and placed constraints on the physical properties of gas clouds in the vicinity ... More
An Arena for Multi-Messenger Astrophysics: Inspiral and Tidal Disruption of White Dwarfs by Massive Black HolesFeb 18 2019The tidal disruption of stars by (super-)massive black holes in galactic nuclei has been discussed in theoretical terms for about 30 years but only in the past decade have we been able to detect such events in substantial numbers. Thus, we are now starting ... More
NGC 3065: A Certified LINER With Broad, Variable Balmer LinesJan 04 2001Motivated by the X-ray properties of the galaxy NGC 3065, we have obtained new optical spectra which reveal that it has a low-ionization nuclear emission-line region (LINER) as well as broad Balmer emission lines, establishing it as an active galactic ... More
Accurate Redshifts and Classifications for 110 Radio-Loud AGNsSep 17 2003Sep 17 2003We report accurate redshifts of 110 active galaxies (mostly radio-loud objects at z<0.4) observed in the course of a survey to find broad, double-peaked emission lines. These redshifts are measured from the narrow emission lines of these objects and are ... More
Radio-loud AGNs: The X-ray perspectiveNov 29 1999The X-ray emission of radio-loud (RL) AGNs is a powerful tool for probing the structure of the accretion flow in these objects. We review recent spectral and variability studies of RL AGNs, which show that these systems have systematically different X-ray ... More
Black Hole Masses of Active Galaxies with Double-Peaked Balmer Emission LinesJan 18 2006We have obtained near-IR spectra of five Active Galactic Nuclei that exhibit double-peaked Balmer Emission Lines (NGC 1097, Pictor A, PKS 0921-213, 1E 0450.30-1817, and IRAS 0236.6-3101). The stellar velocity dispersions of the host galaxies were measured ... More
The ASCA X-Ray Spectrum Of The Broad-Line Radio Galaxy Pictor A: A Simple Power Law With No Fe K-alpha LineApr 24 1998We present the X-ray spectrum of the broad-line radio galaxy Pictor A as observed by ASCA in 1996. The main objective of the observation was to detect and study the profiles of the Fe~K$\alpha$ lines. The motivation was the fact that the Balmer lines ... More
Constraining the central engine of radio-loud AGNsOct 28 1999We present an X-ray spectral survey of radio-loud (RL) AGNs using ASCA and RXTE. The goal was to study the structure of their central engines and compare it to that of their radio-quiet (RQ) counterparts. We find Systematic differences in the X-ray properties ... More
A Radial Velocity Test for Supermassive Black Hole Binaries as an Explanation for Broad, Double-Peaked Emission Lines in Active Galactic NucleiDec 06 2015One of the proposed explanations for the broad, double-peaked Balmer emission lines observed in the spectra of some active galactic nuclei (AGNs) is that they are associated with sub-parsec supermassive black hole (SMBH) binaries. Here, we test the binary ... More
A Tidal Disruption Flare in Abell 1689 from an Archival X-ray Survey of Galaxy ClustersAug 24 2010Theory suggests that a star making a close passage by a supermassive black hole at the center of a galaxy can under most circumstances be expected to emit a giant flare of radiation as it is disrupted and a portion of the resulting stream of shock-heated ... More
Ultra-Close Encounters of Stars With Massive Black Holes: Tidal Disruption Events With Prompt HyperaccretionFeb 19 2015Jun 01 2015A bright flare from a galactic nucleus followed at late times by a $t^{-5/3}$ decay in luminosity is often considered the signature of the complete tidal disruption of a star by a massive black hole. The flare and power-law decay are produced when the ... More
Optical and X-ray Spectroscopy of 1E 0449.4-1823: Demise of the original type 2 QSOFeb 04 1998New optical spectra of the original narrow-line quasar 1E 0449.4-1823 show that it now has broad emission lines of considerable strength, eliminating it as a "type 2 QSO" candidate. We suggest that the behavior of 1E 0449.4-1823 is the same as that of ... More
SDSS J092712.65+294344.0: Recoiling Black Hole or A Sub-parsec Binary Candidate?Sep 18 2008Mar 03 2009A search for recoiling supermassive black hole candidates recently yielded the best candidate thus far, SDSS J092712.65+294344.0 reported by Komossa et al. Here we propose the alternative hypothesis that this object is a supermassive black hole binary. ... More
Interpreting the Variability of Double-Peaked Emission Lines in Active Galactic Nuclei with Stochastically Perturbed Accretion Disk ModelsJun 01 2008In an effort to explain the short-timescale variability of the broad, double-peaked profiles of some active galactic nuclei, we constructed stochastically perturbed accretion disk models and calculated H alpha line profile series as the bright spots rotate, ... More
Variable UV Absorption in the Spectrum of MRC 2251-178Jun 12 2001We present an ultraviolet spectrum of MRC 2251-178 taken with HST/STIS-G230L. The observation is part of a snap shot program of QSOs to systematically search for intrinsic absorption lines through variability. The sample consists of all QSOs observed ... More
Monitoring the Variability of Intrinsic Absorption Lines in Quasar SpectraJul 22 2014We have monitored 12 intrinsic narrow absorption lines (NALs) in five quasars and seven mini-broad absorption lines (mini-BALs) in six quasars for a period of 4-12 years (1-3.5 years in the quasar rest-frame). We present the observational data and the ... More
Emission Lines as a Tool in Search for Supermassive Black Hole Binaries and Recoiling Black HolesSep 02 2009Detection of electromagnetic (EM) counterparts of pre-coalescence binaries has very important implications for our understanding of the evolution of these systems as well as the associated accretion physics. In addition, a combination of EM and gravitational ... More
ASCA Observations of Radio-Loud AGNsNov 02 1998Nov 08 1998We summarize the results of an X-ray spectroscopic survey of radio-loud AGNs observed with ASCA, using proprietary and archival data (public up to 1998 September). We briefly compare our results with those obtained for radio-quiet AGNs studied by other ... More
Spectral Energy Distribution Models for Low-luminosity Active Galactic Nuclei in LINERsDec 20 2011Low-luminosity active galactic nuclei (LLAGNs) represent the bulk of the AGN population in the present-day universe and they trace the low-level accreting supermassive black holes. In order to probe the accretion and jet physical properties in LLAGNs ... More
A Large Systematic Search for Recoiling and Close Supermassive Binary Black HolesJun 15 2011[ABRIDGED] We have carried out a systematic search for close supermassive black hole binaries among z < 0.7 SDSS quasars Such binaries are predicted by models of supermassive black hole and host galaxy co-evolution, therefore their census and population ... More
Feeding the active nucleus of NGC 1097Nov 21 2002We discuss the signatures of an evolving accretion disk around the nucleus of NGC 1097, based on observations of its double-peaked H-alpha emission-line profile which cover a time span of 10 yrs. The monitoring of the profile has allowed us to better ... More
Emission-Line Diagnostics of the Central Engines of Weak-Line Radio GalaxiesApr 22 2003A handful of well-studied Weak-Line Radio Galaxies (WLRGs) have been traditionally classified as Low Ionization Nuclear Emission-line Regions (LINERs), suggesting that these two groups of AGNs might be related. In this paper, we present new optical emission-line ... More
Tidal Disruption of a Star By a Black Hole : Observational SignatureApr 13 2004We have modeled the time-variable profiles of the Halpha emission line from the non-axisymmetric disk and debris tail created in the tidal disruption of a solar-type star by a million solar mass black hole. Two tidal disruption event simulations were ... More
Electromagnetic Signatures of Massive Black Hole BinariesSep 28 2006We model the electromagnetic emission signatures of massive black hole binaries (MBHBs) with an associated gas component. The method comprises numerical simulations of relativistic binaries and gas coupled with calculations of the physical properties ... More
Spectral Models for Low-luminosity Active Galactic Nuclei in LINERs: The Role of Advection-dominated Accretion and JetsDec 06 2013We perform an exploratory study of the physical properties of accretion flows and jets in low-luminosity active galactic nuclei (LLAGNs) by modeling the spectral energy distributions (SEDs) of 12 LLAGNs in low-ionization nuclear emission-line regions ... More
Spectral Energy Distributions of Weak Active Galactic Nuclei Associated With Low-Ionization Nuclear Emission RegionsJan 17 2010We present a compilation of spectral energy distributions of 35 weak AGNs in LINERs using recent data from the published literature. We make use of previously published compilations of data, after complementing and extending them with more recent data. ... More
Observational Signature of Tidal Disruption of a Star by a Massive Black HoleMay 13 2005We have modeled the time-variable profiles of the Balmer alpha emission from the nonaxisymmetric disk and debris tail created in the tidal disruption of a solar-type star by a million solar mass black hole. Two tidal disruption events were simulated using ... More
Long-Term Profile Variability in Active Galactic Nuclei with Double-Peaked Balmer Emission LinesMar 29 2010An increasing number of Active Galactic Nuclei (AGNs) exhibit broad, double-peaked Balmer emission lines,which represent some of the best evidence for the existence of relatively large-scale accretion disks in AGNs. A set of 20 double-peaked emitters ... More
An Assessment of the Energy Budgets of Low-Ionization Nuclear Emission RegionsJan 17 2010Using the SEDs of the weak AGNs 35 LINERs presented in a companion paper, we assess whether photoionization by the weak AGN can power the emission-line luminosities measured through the large (few-arcsecond) apertures used in ground-based spectroscopic ... More
Direct Measurement of Quasar Outflow Wind AccelerationSep 20 2018We search for velocity changes (i.e., acceleration/deceleration) of narrow absorption lines (NALs) that are intrinsic to the quasars, using spectra of 6 bright quasars that have been observed more than once with 8-10m class telescopes. While variations ... More
Emission Line Diagnostics of Accretion Flows in Weak-Line Radio GalaxiesAug 21 2001In recent surveys of Radio-loud AGN, a new sub-class of objects, known as Weak-Line Radio Galaxies (WLRGs) has emerged. These radio galaxies have only weak, low-ionization optical emission lines. In the X-ray band, these objects are much fainter and have ... More
Modeling of Emission Signatures of Massive Black Hole Binaries: I MethodsAug 02 2007We model the electromagnetic signatures of massive black hole binaries (MBHBs) with an associated gas component. The method comprises numerical simulations of relativistic binaries and gas coupled with calculations of the physical properties of the emitting ... More
A Chandra Look at Five of the Broadest Double-Peaked Balmer-Line EmittersAug 06 2008We study the 0.5-10keV emission of a sample of five of the broadest double-peaked Balmer-line emitters with Chandra. The Balmer lines of these objects originate close (within a few hundred gravitational radii) to the central black holes of the Active ... More
Discovery of a Hard X-Ray Source, SAX J0635+0533, in the Error Box of the Gamma-Ray Source 2EG 0635+0521Apr 19 1999We have discovered an x-ray source, SAX J0635+0533, with a hard spectrum within the error box of the GeV gamma-ray source in Monoceros, 2EG J0635+0521. The unabsorbed x-ray flux is 1.2*10^-11 erg cm^-2 s^-1 in the 2-10 keV band. The x-ray spectrum is ... More
On the Covering Fraction Variability in an EUV Mini-BAL Outflow from PG 1206+459Sep 25 2015Jan 13 2016We report on the first detection of extreme-ultraviolet (EUV) absorption variability in the NeVIII 770,780 mini-broad absorption line (mini-BAL) in the spectrum of the quasar (QSO) PG 1206+459. The observed equivalent width (EW) of the NeVIII doublet ... More
Observational Signature of Tidal Disruption of a Star by a Massive Black HoleApr 12 2004We have modeled the time-variable profiles of the Halpha emission line from the non-axisymmetric disk and debris tail created in the tidal disruption of a solar-type star by a million solar mass black hole. We find that the line profiles at these very ... More
Exploratory Study of the X-Ray Properties of Quasars With Intrinsic Narrow Absorption LinesJan 10 2008We have used archival Chandra and XMM-Newton observations of quasars hosting intrinsic narrow UV absorption lines (intrinsic NALs) to carry out an exploratory survey of their X-ray properties. Our sample consists of three intrinsic-NAL quasars and one ... More
Results of Monitoring the Dramatically Variable C IV Mini-BAL System in the Quasar HS 1603+3820Jan 23 2007We present six new and two previously published high-resolution spectra of the quasar HS 1603+3820 (z_em = 2.542) taken over an interval of 4.2 years (1.2 years in the quasar rest frame). The observations were made with the High-Dispersion Spectrograph ... More
Luminous [O III] and [N II] from Tidally Disrupted Horizontal Branch StarsMay 14 2012We model the emission lines generated in the photoionised debris of a tidally disrupted horizontal branch star. We find that at late times, the brightest optical emission lines are [N II] \lambda\lambda 6548,6583 and [O III] \lambda\lambda 4959,5007. ... More
The Size of the Broad Line Region in M84 (NGC 4374)Aug 13 2010Aug 25 2010M84 is a giant elliptical galaxy located in the Virgo cluster. Prior imaging with the Hubble Space Telescope (HST) revealed a small, highly inclined, nuclear ionized gas disk, the kinematics of which indicate the presence of a 0.4 -1.5 billion solar mass ... More
A Study of QSO Evolution in the X-Ray Band with the Aid of Gravitational LensingJan 03 2004We present results from a mini-survey of relatively high redshift (1.7 < z < 4) gravitationally lensed radio-quiet quasars observed with the Chandra X-ray Observatory and with XMM-Newton. The lensing magnification effect allows us to search for changes ... More
Time-Variable Complex Metal Absorption Lines in the Quasar HS1603+3820Apr 29 2005We present a new spectrum of the quasar HS1603+3820 taken 1.28 years (0.36 years in the quasar rest frame) after a previous observation with Subaru+HDS. The new spectrum enables us to search for time variability as an identifier of intrinsic narrow absorption ... More
Intrinsic Narrow Absorption Lines in HIRES/Keck Spectra of a Sample of Six QuasarsFeb 24 1999In the course of a large intervening MgII survey of 25 quasars, the CIV emission lines of six (three radio-loud and three radio-quiet) were observed serendipitously. In four of these six quasars, we detected associated narrow absorption lines. Three of ... More
Advection-dominated accretion, jets and the spectral energy distribution of LINERsJan 19 2010Low-luminosity active galactic nuclei (LLAGNs) represent the bulk of the AGN population in the present-day universe and they trace low-level accreting supermassive black holes. The observational properties of LLAGNs suggest that their central engines ... More
Discovery of the Transition of a Mini-Broad Absorption Line into Broad Absorption in the SDSS Quasar J115122.14+020426.3Jul 23 2013We present the detection of a rare case of dramatic strengthening in the UV absorption profiles in the spectrum of the quasar J115122.14+020426.3 between observations ~2.86 years apart in the quasar rest-frame. A 2001 spectrum from the Sloan Digital Sky ... More
Emission Signatures from Sub-parsec Binary Supermassive Black Holes II: Effect of Accretion Disk Wind on Broad Emission LinesJul 25 2018Nov 14 2018We present an improved semi-analytic model for calculation of the broad optical emission-line signatures from sub-parsec supermassive black hole binaries (SBHBs) in circumbinary disks. The second-generation model improves upon the treatment of radiative ... More
Black Holes at the Centers of Nearby Dwarf GalaxiesAug 19 2014Using a distance-limited portion of the Sloan Digital Sky Survey (SDSS) Data Release 7, we have identified 28 active galactic nuclei (AGNs) in nearby (d < 80 Mpc) low-mass, low-luminosity dwarf galaxies. The accreting objects at the galaxy centers are ... More
A Simultaneous RXTE and XMM-Newton Observation of the Broad-Line Radio Galaxy 3C 111Dec 20 2004We present the results of simultaneous XMM-Newton and RXTE observations of the Broad-Line Radio Galaxy 3C 111. We find that the Compton reflection bump is extremely weak, however, broad residuals are clearly present in the spectrum near the Fe Kalpha ... More
Radiatively Inefficient Accretion Flow in the Nucleus of NGC 1097Dec 21 2005We present a model for the accretion flow around the supermassive black hole in the LINER nucleus of NGC 1097 which fits the optical to X-ray spectral energy distribution (SED). The X-ray segment of the SED is based on observations with the Chandra X-Ray ... More
The Physical Conditions of the Intrinsic N V Narrow Absorption Line Systems of Three QuasarsAug 17 2010We employ detailed photoionization models to infer the physical conditions of intrinsic narrow absorption line systems found in high resolution spectra of three quasars at z=2.6-3.0. We focus on a family of intrinsic absorbers characterized by N V lines ... More
Short timescale variations of the Hα double-peaked profile of the nucleus of NGC 1097Mar 27 2012The broad (FWHM ~ 10,000 km/s) double-peaked H{\alpha} profile from the LINER/Seyfert 1 nucleus of NGC 1097 was discovered in 1991, and monitored for the following 11 years. The profile showed variations attributed to the rotation of gas in a non-axisymmetric ... More
Long Term Profile Variability of Double-Peaked Emission Lines in AGNsSep 23 2003An increasing number of AGNs exhibit broad, double-peaked Balmer emission lines, which are thought to arise from the outer regions of the accretion disk which fuels the AGN. The line profiles are observed to vary on a characteristic timescales of 5-10 ... More
Reverberation Mapping of the Broad Line Region: application to a hydrodynamical line-driven disk wind solutionJan 20 2016Apr 23 2016The latest analysis efforts in reverberation mapping are beginning to allow reconstruction of echo images (or velocity-delay maps) that encode information about the structure and kinematics of the broad line region (BLR) in active galactic nuclei (AGNs). ... More
On the Origin of Intrinsic Narrow Absorption Lines in z<1 QSOsOct 10 2000We present a statistical analysis of the associated, high ionization narrow absorption line (NAL) systems in a sample of 59 QSOs defined from the HST QSO Absorption Line Key Project. We have compiled the QSO luminosities at 2500 A, 5 GHz, and 2 keV, spectral ... More
Transient and Highly Polarized Double-Peaked H-alpha Emission in the Seyfert 2 Nucleus of NGC 2110Aug 23 2007We have discovered an extremely broad, double-peaked H-alpha emission line in the polarized flux spectrum of NGC 2110, establishing that this well-studied Seyfert 2 galaxy contains a disk-like hidden broad-line region (BLR). Several properties of NGC ... More
Measurement of an AGN Central Mass on Centiparsec Scales: Results of Long-Term Optical Monitoring of Arp 102BMar 05 1997The optical spectrum of the broad-line radio galaxy Arp 102B has been monitored for more than thirteen years to investigate the nature of the source of its broad, double-peaked hydrogen Balmer emission lines. The shape of the lines varied subtly; there ... More
Long-Term Profile Variability of Double-Peaked Emmission Lines in AGNsApr 16 2004An increasing number of AGNs exhibit broad, double-peaked Balmer emission lines, which arise from the outer regions of the accretion disk which fuels the AGN. The line profiles vary on timescales of 5--10 years. Our group has monitored a set of 20 double-peaked ... More
The Ages of High Mass X-ray Binaries in NGC 2403 and NGC 300May 21 2013We have examined resolved stellar photometry from HST imaging surrounding 18 high-mass X-ray binary (HMXB) candidates in NGC 300 and NGC 2403 as determined from combined Chandra/HST analysis. We have fit the color-magnitude distribution of the surrounding ... More
Black Holes in Bulgeless Galaxies: An XMM-Newton Investigation of NGC 3367 and NGC 4536Dec 03 2010The vast majority of optically identified active galactic nuclei (AGNs) in the local Universe reside in host galaxies with prominent bulges, supporting the hypothesis that black hole formation and growth is fundamentally connected to the build-up of galaxy ... More
Where are the Intermediate Mass Black Holes?Mar 19 2019Observational evidence has been mounting for the existence of intermediate mass black holes (IMBHs, 10^2-10^5 Msun), but observing them at all, much less constraining their masses, is very challenging. In one theorized formation channel, IMBHs are the ... More
Multi-Messenger Astrophysics with Pulsar Timing ArraysMar 18 2019Pulsar timing arrays (PTAs) are on the verge of detecting low-frequency gravitational waves (GWs) from supermassive black hole binaries (SMBHBs). With continued observations of a large sample of millisecond pulsars, PTAs will reach this major milestone ... More
A Large Systematic Search for Close Supermassive Binary and Rapidly Recoiling Black Holes - II. Continued Spectroscopic Monitoring and Optical Flux VariabilitySep 08 2015Sep 11 2015We present new spectroscopic observations that are part of our continuing monitoring campaign of 88 quasars at z<0.7 whose broad H$\beta$ lines are offset from their systemic redshifts by a few thousand km/s. These quasars have been considered candidates ... More
The Post-Common Envelope and Pre-Cataclysmic Binary PG 1224+309Nov 24 1998We have made extensive spectroscopic and photometric observations of PG 1224+309, a close binary containing a DA white dwarf primary and an M4+ secondary. The H alpha line is in emission due to irradiation of the M-star by the hot white dwarf and is seen ... More
HST Observations of IP Pegasi in Quiescence: The Pre-Eclipse SpectrumApr 04 1997We present time-resolved HST UV spectroscopy and ground-based optical photometry of the dwarf nova IP Peg in a quiescent state. The observations were obtained prior to an eclipse, when the bright spot caused by the impact of the accretion stream with ... More
Gemini Imaging of the Host Galaxies of Changing-Look QuasarsMar 19 2019Changing-look quasars are a newly-discovered class of luminous active galactic nuclei that undergo rapid ($\lesssim$10 year) transitions between Type 1 and Type 1.9/2, with an associated change in their continuum emission. We characterize the host galaxies ... More
Formation Timescales for High-Mass X-ray Binaries in M33Jun 18 2018We have identified 55 candidate high-mass X-ray binaries (HMXBs) in M33 using available archival {\it HST} and {\it Chandra} imaging to find blue stars associated with X-ray positions. We use the {\it HST} photometric data to model the color-magnitude ... More
Gemini Imaging of the Host Galaxies of Changing-Look QuasarsMar 19 2019Apr 01 2019Changing-look quasars are a newly-discovered class of luminous active galactic nuclei that undergo rapid ($\lesssim$10 year) transitions between Type 1 and Type 1.9/2, with an associated change in their continuum emission. We characterize the host galaxies ... More
Extreme X-ray Behavior of the Low-Luminosity Active Nucleus in NGC 4395Feb 04 2005We present the results of a 17 ks Chandra ACIS-S observation of the nearby dwarf spiral galaxy NGC 4395. Chandra affords the first high-quality, broadband X-ray detection of the active nucleus of this object that is uncontaminated by nearby sources in ... More
The Effect of Variability on X-Ray Binary Luminosity Functions: Multiple Epoch Observations of NGC 300 with ChandraNov 14 2016We have obtained three epochs of Chandra ACIS-I observations (totaling $\sim$184 ks) of the nearby spiral galaxy NGC~300 to study the logN-logS distributions of its X-ray point source population down to $\sim$2$\times$10$^{-15}$ erg s$^{-1}$ cm$^{-2}$ ... More
Extreme-Velocity Quasar Outflows and the Role of X-ray ShieldingJul 03 2013Quasar accretion disk winds observed via broad absorption lines (BALs) in the UV produce strong continuous absorption in X-rays. The X-ray absorber is believed to serve critically as a radiative shield to enable radiative driving. However, "mini-BAL" ... More
The Physics and Physical Properties of Quasar OutflowsFeb 01 2013We describe two studies designed to characterize the total column densities, kinetic energies, and acceleration physics of broad absorption line (BAL) outflows in quasars. The first study uses new Chandra X-ray and ground-based rest-frame UV observations ... More
Double-peaked profiles: ubiquitous signatures of disks in the Broad Emission Lines of Active Galactic NucleiDec 20 2016Broad (~10,000 km/s), double-peaked emission-line profiles of Balmer lines emitted by active galactic nuclei (AGN) are thought to originate in the outer parts of an accretion disk surrounding a nuclear supermassive black hole (SMBH), at R~1000 gravitational ... More
Multi-Sightline Observation of Narrow Absorption Lines in Lensed Quasar SDSS J1029+2623May 04 2016We exploit the widely-separated images of the lensed quasar SDSS J1029+2623 ($z_{em}$=2.197, $\theta =22^{\prime\prime}\!\!.5$) to observe its outflowing wind through two different sightlines. We present an analysis of three observations, including two ... More
Where are the Intermediate Mass Black Holes?Mar 19 2019Mar 22 2019Observational evidence has been mounting for the existence of intermediate mass black holes (IMBHs, 10^2-10^5 Msun), but observing them at all, much less constraining their masses, is very challenging. In one theorized formation channel, IMBHs are the ... More
The Time Domain Spectroscopic Survey: Variable Object Selection and Anticipated ResultsMay 04 2015We present the selection algorithm and anticipated results for the Time Domain Spectroscopic Survey (TDSS). TDSS is an SDSS-IV eBOSS subproject that will provide initial identification spectra of approximately 220,000 luminosity-variable objects (variable ... More
Large-Amplitude X-ray Outbursts from Galactic Nuclei: A Systematic Survey Using ROSAT Archival DataJun 17 2002In recent years, luminous X-ray outbursts with variability amplitudes as high as ~ 400 have been serendipitously detected from a small number of active and inactive galaxies. These outbursts may result from the tidal disruptions of stars by supermassive ... More
Double-Peaked Broad Emission Lines in NGC 4450 and Other LINERsApr 28 2000Spectra taken with HST reveal that NGC 4450 emits Balmer emission lines with displaced double peaks and extremely high-velocity wings. This characteristic line profile, previously seen in a few nearby LINERs and in a small fraction of broad-line radio ... More
The Discovery of the First "Changing Look" Quasar: New Insights into the Physics & Phenomenology of AGNDec 05 2014Jan 20 2015SDSS J015957.64+003310.5 is an X-ray selected, $z=0.31$ AGN from the Stripe 82X survey that transitioned from a Type 1 quasar to a Type 1.9 AGN between 2000 and 2010. This is the most distant AGN, and first quasar, yet observed to have undergone such ... More
A Large Systematic Search for Close Supermassive Binary and Rapidly Recoiling Black Holes - III. Radial Velocity VariationsFeb 17 2017We have been spectroscopically monitoring 88 quasars selected to have broad H$\beta$ emission lines offset from their systemic redshift by thousands of km s$^{-1}$. By analogy with single-lined spectroscopic binary stars, we consider these quasars to ... More
Astro2020 Decadal Science White Paper: Gravitational Wave Survey of Galactic Ultra Compact BinariesMar 13 2019Ultra-compact binaries (UCBs) are systems containing compact or degenerate stars with orbital periods less than one hour. Tens of millions of UCBs are predicted to exist within theGalaxy emitting gravitational waves (GWs) at mHz frequencies. Combining ... More
The Analogous Structure of Accretion Flows in Supermassive and Stellar Mass Black HolesMar 06 2019Black holes grow rapidly through the accretion of gas. As the accretion rate onto a black hole decreases, the structure of its surrounding accretion flow is believed to dramatically transition from a luminous thin disc to become quasi-spherical and radiatively ... More
Short-Timescale monitoring of the X-ray, UV and broad double-peak emission line of the nucleus of NGC 1097Nov 17 2014Recent studies have suggested that the short-timescale ($\lesssim7$ days) variability of the broad ($\sim$10,000 km s$^{-1}$) double-peaked H$\alpha$ profile of the LINER nucleus of NGC1097 could be driven by a variable X-ray emission from a central radiatively ... More
New Ultraviolet Observations of AM CVnJul 16 2007We have obtained observations of the ultraviolet spectrum of AM CVn, an ultra-short-period helium cataclysmic variable, using the Space Telescope Imaging Spectrograph (STIS) aboard the Hubble Space Telescope (HST). We obtained data in time-tag mode during ... More
Probing Quiescent Massive Black Holes: Insights from Tidal Disruption EventsMar 05 2009Tidal disruption events provide a unique probe of quiescent black holes in the nuclei of distant galaxies. The next generation of synoptic surveys will yield a large sample of flares from the tidal disruption of stars by massive black holes that will ... More
Completion of a Survey and Detailed Study of Double-Peaked Emission Lines in Radio-Loud AGNsSep 04 2003Sep 17 2003We report the completion of a survey of radio-loud AGNs begun in an earlier paper, aimed finding and studying broad, double-peaked Balmer lines. We present Ha spectra of 13 broad-lined objects (3 with double-peaked Ha profiles). The final sample includes ... More
A Census of Quasar-Intrinsic Absorption in the Hubble Space Telescope Archive: Systems from High Resolution Echelle SpectraJul 25 2013We present a census of z(abs) < 2, intrinsic (those showing partial coverage) and associated [z(abs) ~ z(em)] quasar absorption-line systems detected in the Hubble Space Telescope archive of Space Telescope Imaging Spectrograph echelle spectra. This work ... More
Long-Term, Continuous Monitoring of the Broad Line Radio Galaxies 3C 390.3 and 3C 120 With the Rossi X-Ray Timing ExplorerOct 14 2002We present a study of the flux and spectral variability of the two broad-line radio galaxies (BLRGs) 3C 390.3 and 3C 120, observed almost daily with RXTE for nearly two months each in 1996 and 1997, respectively. Our original motivation for this study ... More
Long-Term Profile Variability of Double Peaked Emission Lines in Active Galactic NucleiFeb 21 2007We present up to two decades of spectroscopic monitoring of the double-peaked broad Halpha emission lines of seven broad-line radio galaxies. These extremely broad, double-peaked lines are successfully modeled by emission from gas in the outer accretion ... More
E 0336-248 : A New BL Lac Object Found by an Old EinsteinAug 04 1997We obtained new ROSAT HRI and optical observations in the field of the Einstein X-ray source E 0336-248, which we use to identify it as a 19th magnitude BL Lacertae object at z=0.251 with an X-ray luminosity of 10^45 erg/s. It is also a 14 mJy radio source ... More
Comparing Chandra and Hubble in the Northern Disk of M31Aug 30 2018The X-ray source populations within galaxies are typically difficult to identify and classify from X-ray data alone. We are able to break through this barrier by combining deep new Chandra ACIS-I observations with extensive Hubble Space Telescope imaging ... More
Luminous Thermal Flares from Quiescent Supermassive Black HolesApr 09 2009Apr 29 2009A dormant supermassive black hole lurking in the center of a galaxy will be revealed when a star passes close enough to be torn apart by tidal forces, and a flare of electromagnetic radiation is emitted when the bound fraction of the stellar debris falls ... More
The Chandra Local Volume Survey: The X-ray Point Source Catalog of NGC 300Aug 07 2012We present the source catalog of a new Chandra ACIS-I observation of NGC 300 obtained as part of the Chandra Local Volume Survey. Our 63 ks exposure covers ~88% of the D25 isophote (R~6.3 kpc) and yields a catalog of 95 X-ray point sources detected at ... More
Now You See It, Now You Don't: The Disappearing Central Engine of the Quasar J1011+5442Sep 11 2015We report the discovery of a new "changing-look" quasar, SDSS J101152.98+544206.4, through repeat spectroscopy from the Time Domain Spectroscopic Survey. This is an addition to a small but growing set of quasars whose blue continua and broad optical emission ... More
A $Chandra-Swift$ View of Point Sources in Hickson Compact Groups: High AGN fraction but a dearth of strong AGNsMar 15 2014We present $Chandra$ X-ray point source catalogs for 9 Hickson Compact Groups (HCGs, 37 galaxies) at distances $34 - 89$ Mpc. We perform detailed X-ray point source detection and photometry, and interpret the point source population by means of simulated ... More
The End of the Lines for OX 169: No Binary Broad-Line RegionOct 06 1999We show that unusual Balmer emission line profiles of the quasar OX 169, frequently described as either self-absorbed or double peaked, are actually neither. The effect is an illusion resulting from two coincidences. First, the forbidden lines are quite ... More
Simulating the Early Evolution of the Hard X-Ray Properties of a Young Stellar PopulationAug 05 2003We present an X-ray binary population synthesis model, and use it to simulate the evolution of X-ray binaries formed in a burst of star formation of duration 20 Myr and star-formation rate 10 M_sun/yr. Our goal is to explain the hard (2-10 keV) X-ray ... More