Karen Lewis - Academia.edu (original) (raw)

Papers by Karen Lewis

Cornell University - arXiv, Aug 21, 2001

In recent surveys of Radio-loud AGN, a new sub-class of objects, known as Weak-Line Radio Galaxie... more In 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 flatter spectra than broad-line and narrow-line radio galaxies. In these respects, WLRGs are reminiscent of Low Ionization Nuclear Emission Regions (LINERs). We have begun a multi-wavelength study of WLRGs to better understand their possible connection to LINERs and the structure of the accretion flow in both these systems. Here, we present new optical spectra of a sample of WLRGs. We find that 81% of the objects have optical emission-line properties that are similar to LINERs, indicating that these two classes of AGN may be related. Future high resolution X-ray observations of WLRGs will be critical in determining the true nature of the accretion flow in these objects.

Bulletin of the American Astronomical Society, Dec 1, 2004

An increasing number of AGNs exhibit broad, double-peaked Balmer emission lines, which are though... more An 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 years. The variability is not a reverberation effect; it is a manifestation of physical changes in the disk. Our group has monitored a set of 20 double-peaked emitters for the past 8 years (longer for some objects). Here, we characterize the variability of the double-peaked Hα line profiles in five objects from our sample. By experimenting with simple models, we find that disks with a single precessing spiral arm are able to reproduce many of the variability trends that are seen in the data.

Noao Proposal, Feb 1, 2007

The XMM Slew Survey is projected to cover 80% of the sky in the soft (0.5--2 keV) and hard (2--10... more The XMM Slew Survey is projected to cover 80% of the sky in the soft (0.5--2 keV) and hard (2--10 keV) bands. The survey has a flux limit of 4 × 10-12 erg s-1 cm-2 in the hard band. Like all hard-band surveys, it has the ability to detect even heavily absorbed AGN, and the large area coverage makes it

An increasing number of active galactic nuclei (AGN) exhibit broad, double-peaked Balmer emission... more An increasing number of active galactic nuclei (AGN) exhibit broad, double-peaked Balmer emission lines that originate in the outer accretion disk of the AGN. The line profiles have been observed to vary on timescales of several months to years. Over the past decade, our group has monitored a set of 20 double-peaked emitters. Here we characterize the variability patterns of

The Swift Gamma-Ray Burst satellite has detected a largely unbiased towards absorption sample of ... more The Swift Gamma-Ray Burst satellite has detected a largely unbiased towards absorption sample of local (< z >≈ 0.03) AGN, based solely on their 14-195 keV flux. In the first 9 months of the survey, 153 AGN sources were detected. The X-ray properties in the 0.3-10 keV band have been compiled and presented based on analyses with XMM-Newton, Chandra, Suzaku, and the Swift XRT (Winter et al. 2009). Additionally, we have compiled a sub-sample of sources with medium resolution optical ground-based spectra from the SDSS or our own observations at KPNO. In this sample of 60 sources, we have classified the sources using standard emission line diagnostic plots, obtained masses for the broad line sources through measurement of the broad Hβ emission line, and measured the [OIII] 5007Å luminosity of this sample. Based on continuum fits to the intrinsic absorption features, we have obtained clues about the stellar populations of the host galaxies. We now present the highlights of our X-ray and optical studies of this unique sample of local AGNs, including a comparison of the 2-10 keV and 14-195 keV X-ray luminosities with the [OIII] 5007Å luminosity and the implications of our results towards measurements of bolometric luminosities.

The Swift Burst Alert Telescope (BAT), while not focused on a Gamma-ray burst, conducts an all-sk... more The Swift Burst Alert Telescope (BAT), while not focused on a Gamma-ray burst, conducts an all-sky survey in the 14 - 195 keV band. After the first 9 months, the BAT has detected a sample of 153 local (z 0.03) AGN at a flux limit of a few times 10-11 erg/s/cm-2 (Tueller et al. 2007). Since the AGN were detected

We present new results from a 40.8 ks Chandra ACIS observation of the young supernova remnant (SN... more We present new results from a 40.8 ks Chandra ACIS observation of the young supernova remnant (SNR) N103B located in the Large Magellanic Cloud. The high resolution Chandra image reveals structure at the sub-arcsecond level, including several bright knots and filaments. Narrow-band imaging and spatially resolved spectroscopy reveal dramatic spectral variations in this remnant as well. In this paper we

We present the results of a simultaneous XMM-Newton and RXTE observation of the Broad-Line Radio ... more We present the results of a simultaneous XMM-Newton and RXTE observation 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 K alpha line. When fit with a Gaussian emission line, the feature has an equivalent width of 60±20 eV and

The Astrophysical Journal, 2005

We present the results of simultaneous XMM-Newton and RXTE observations of the Broad-Line Radio G... more We 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 Kα emission line region. When fitted with a Gaussian emission line, the feature has an equivalent width of 40-100 eV and full-width at half maximum of greater than 20,000 km s −1 , however the exact properties of this weak line are highly dependent upon the chosen continuum model. The width of the line suggests an origin in the inner accretion disk, which is, however, inconsistent with the lack of Compton reflection. We find that much of the broad residual emission can be attributed to continuum curvature. The data are consistent with a model in which the primary powerlaw continuum is reprocessed by an accretion disk which is truncated as small radii. Alternatively, the primary source could be partially covered by a dense absorber. The latter model is less attractive than the former because of the small inclination angle of the jet of 3C 111 to the line of sight. We consider it likely that the curved continuum of the partial covering model is fortuitously similar to the continuum shape of the reprocessing model. In both models, the fit is greatly improved by the addition of an unresolved Fe Kα emission line, which could arise either in a Compton-thin obscuring torus or dense clouds lying along the line of sight. We also find that there are unacceptable residuals at low energies in the MOS data in particular, which were modeled as a Gaussian with an energy of ∼ 1.5 keV; we attribute these residuals to calibration uncertainties of the MOS detectors.

The Astrophysical Journal, 2010

The Swift Burst Alert Telescope (BAT) survey of Active Galactic Nuclei (AGN) is providing an unpr... more The Swift Burst Alert Telescope (BAT) survey of Active Galactic Nuclei (AGN) is providing an unprecedented view of local AGNs (< z >≈ 0.03) and their host galaxy properties. In this paper, we present an analysis of the optical spectra of a sample of 64 AGNs from the 9-month survey, detected solely based on their 14-195 keV flux. Our analysis includes both archived spectra from the Sloan Digital Sky Survey and our own observations from the 2.1-m Kitt Peak National Observatory telescope. Among our results, we include line ratio classifications utilizing standard emission line diagnostic plots, [O III] 5007Å luminosities, and Hβ derived black hole masses. As in our Xray study, we find the type 2 sources to be less luminous (in [O III] 5007Å and 14-195 keV luminosities) with lower accretion rates than the type 1 sources. We find that the optically classified LINERs, H II/composite galaxies, and ambiguous sources have the lowest luminosities, while both broad line and narrow line Seyferts have similar luminosities. From a comparison of the hard X-ray (14-195 keV) and [O III] luminosities, we find that both the observed and extinction-corrected [O III] luminosities are weakly correlated with X-ray luminosity. In a study of the host galaxy properties from both continuum fits and measurements of the stellar absorption indices, we find that the hosts of the narrow line sources have properties consistent with late type galaxies.

The Astrophysical Journal, 2009

We present XMM-Newton and Suzaku observations of the broad-line radio galaxy 3C 390.3 acquired in... more We present XMM-Newton and Suzaku observations of the broad-line radio galaxy 3C 390.3 acquired in 2004 October and 2006 December, respectively. An archival Swift BAT spectrum from the 9 month survey is also analyzed, as well as an optical spectrum simultaneous to XMM-Newton. At soft X-rays, no absorption features are detected in the Reflection Grating Spectrometer spectrum of 3C 390.3; a narrow emission line is found at 0.564 keV, most likely originating in the narrow-line region. Both the EPIC and XIS data sets confirm the presence of an Fe Kα emission line at 6.4 keV with equivalent width (EW) = 40 eV. The Fe Kα line has a width FWHM ∼ 8800 km s −1 , consistent within a factor of 2 with the width of the double-peaked Hα line, suggesting an origin from the broad-line region. The data show for the first time a weak, broad bump extending from 5 to 7 keV. When fitted with a Gaussian, its centroid energy is 6.6 keV in the source's rest frame with FWHM of 43,000 km s −1 and EW of 50 eV; its most likely interpretation is emission from He-like Fe (Fe xxv), suggesting the presence of an ionized medium in the inner regions of 3C 390.3. The broadband 0.5-100 keV continuum is well described by a single power law with photon index Γ = 1.6 and cutoff energy 157 keV, plus cold reflection with strength R = 0.5. In addition, ionized reflection is required to account for the 6.6 keV bump in the broadband continuum, yielding an ionization parameter ξ ∼ 2700 erg cm s −1 ; the inner radius of the ionized reflector is constrained to be larger than 20r G , although this result depends on the assumed emissivity profile of the disk. If true, we argue that the lack of broad Fe K emission from within 20r G indicates that the innermost regions of the disk in 3C 390.3 are obscured and/or poorly illuminated. While the spectral energy distribution (SED) of 3C 390.3 is generally dominated by accretionrelated continuum, during accretion low states the jet can significantly contribute in the optical to X-ray bands via synchrotron self-Compton emission. The Compton component is expected to extend to and peak at GeV gamma rays where it will be detected with the Fermi Gamma-Ray Space Telescope during its first few years of operation.

The Astrophysical Journal, 2003

We report on the results from a Chandra ACIS observation of the young, compact, supernova remnant... more We report on the results from a Chandra ACIS observation of the young, compact, supernova remnant N103B. The unprecedented spatial resolution of Chandra reveals sub-arcsecond structure, both in the brightness and in spectral variations. Underlying these small-scale variations is a surprisingly simple radial structure in the equivalent widths of the strong Si and S emission lines. We investigate these radial variations through spatially resolved spectroscopy using a plane-parallel, non-equilibrium ionization model with multiple components. The majority of the emission arises from components with a temperature of 1 keV: a fully ionized hydrogen component; a high ionization timescale (n e t> 10 12 s cm −3) component containing Si, S, Ar, Ca, and Fe; and a low ionization timescale (n e t∼10 11 s cm −3) O, Ne, and Mg component. To reproduce the strong Fe Kα line, it is necessary to include additional Fe in a hot (> 2 keV), low ionization (n e t∼10 10.8 s cm −3) component. This hot Fe may be in the form of hot Fe bubbles, formed in the radioactive decay of clumps of 56 Ni. We find no radial variation in the ionization timescales or temperatures of the various components. Rather, the Si and S equivalent widths increase at large radii because these lines, as well as those of Ar and Ca, are formed in a shell occupying the outer half of the remnant. A shell of hot Fe is located interior to this, but there is a large region of overlap between these two shells. In the inner 30% of the remnant, there is a core of cooler, 1 keV Fe. We find that the distribution of the ejecta and the yields of the intermediate mass species are consistent with model prediction for Type Ia events.

The Astrophysical Journal, 2003

A handful of well-studied Weak-Line Radio Galaxies (WLRGs) have been traditionally classified as ... more A handful of well-studied Weak-Line Radio Galaxies (WLRGs) have been traditionally classified as Low Ionization Nuclear Emission-line Regions (LIN-ERs), suggesting that these two groups of AGNs might be related. In this paper, we present new optical emission-line measurements for twenty Weak-Line Radio Galaxies which we supplement with measurements for an additional four from the literature. Classifying these objects by their emission-line ratios, we find that 50% of the objects are robustly classified as LINERs while an additional 25% are likely to be LINERs. Photoionization calculations show that the Spectral Energy Distribution of the well-studied WLRG 3C 270 (NGC 4261) is able to produce the observed emission-line ratios, but only if the UV emission seen by the narrow emission-line gas is significantly higher than that observed, implying A V = 2.5-4.2 magnitudes along our line of sight to the nucleus. From the photoionization calculations, we find that the emission-line gas must have an ionization parameter between 10 −3.5 and 10 −4.0 and a wide range in hydrogen density (10 2-10 6 cm −3) to reproduce the measured emission-line ratios, similar to the properties inferred for the emission-line gas in LINERs. Thus, we find that properties of the emission-line gas as well as the underlying excitation mechanism are indeed similar in LINERs and WLRGs. By extension, the central engines of accretionpowered LINERs and WLRGs, which do host an accreting black hole, may be qualitatively similar.

The Astrophysical Journal, 2006

We have obtained near-IR spectra of five Active Galactic Nuclei that exhibit double-peaked Balmer... more We 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 from the Ca ii λλ8494, 8542, 8662Å absorption lines and were found to range from 140 to 200 km s −1. Using the well-known correlation between the black hole mass and the stellar velocity dispersion, the black hole masses in these galaxies were estimated to range from 4 × 10 7 to 1.2 × 10 8 M ⊙. We supplement the observations presented here with estimates of the black holes masses for five additional double-peaked emitters (Arp 102B, 3C 390.3, NGC 4579, NGC 4203, and M81) obtained by other authors using similar methods. Using these black hole masses, we infer the ratio of the bolometric luminosity to the Eddington luminosity, (L bol /L Edd). We find that two objects (Pictor A and PKS 0921-213) have L bol /L Edd ∼ 0.2, whereas the other objects have L bol /L Edd 10 −2 (nearby, low-luminosity double-peaked emitters are the most extreme, with L bol /L Edd 10 −4). The physical time scales in the outer regions of the accretion disks (at r ∼ 10 3 GM/c 2) in these objects were also estimated and range from a few months, for the dynamical time scale, to several decades for the sound crossing time scale. The profile variability in these objects are typically an order of magnitude longer than the dynamical time, but we note that variability occurring on the dynamical time scale has not been ruled out by the observations.

The Astronomical Journal, 2011

We present the results from exploratory (12-23 ks) XMM-Newton observations of six optically selec... more We present the results from exploratory (12-23 ks) XMM-Newton observations of six optically selected, radio-loud active galactic nuclei (AGNs), together with new radio data and a reanalysis of their archival SDSS spectra. The sources were selected in an effort to expand the current sample of radio-loud AGNs suitable for detailed X-ray spectroscopy studies. The sample includes three broad-line and three

New Astronomy Reviews, 2009

Broad, double-peaked, Balmer emission lines are found in the optical spectra of a relatively smal... more Broad, double-peaked, Balmer emission lines are found in the optical spectra of a relatively small fraction of active galactic nuclei. They can be an extremely useful diagnostic for the structure and dynamics of the ''broad-line region" (the medium that emits the broad emission lines). In general terms the rarity and shapes of their profiles provide strong constraints on universal models of the broad-line region. A series of observational tests and basic physical considerations suggest that these lines are emitted from a flat, rotating disk, very likely the outer parts of the accretion disk that fuels the black hole. In the context of models for accretion disk winds, double-peaked emission lines originate in disks with feeble winds of low optical depth. Therefore, they provide evidence that the outer accretion disk and its associated wind are the source of the broad emission lines. Within this framework, double-peaked Balmer emission lines and corresponding high-ionization lines in the near-ultraviolet allow us to study the conditions under which the winds become dense and the onset of significant outflows. Moreover, double-peaked emission lines give us a direct view of the dense material of the disk proper and allow us to study dynamical perturbations and other transient behavior though the long-term variability of their profiles.

The Astrophysical Journal Supplement Series, 2007

We present up to two decades of spectroscopic monitoring of the double-peaked broad Hα emission l... more We present up to two decades of spectroscopic monitoring of the double-peaked broad Hα 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 disk, and their profiles vary on timescales of months to years. This variability is a valuable probe for understanding the structure and dynamics of the accretion disk. We characterize the long-term broad-line profile variability in detail, and compare the evolution of the line profiles with predictions from a few simple physical models for dynamical processes in the accretion disk. We find no evidence for persistent, periodic variability that would be indicative of a precessing elliptical disk, or a circular disk with a long-lived, single-armed spiral or warp. We do find transient, periodic variability on the orbital timescale, possibly resulting from shocks induced by tidal perturbations, and variability in the wings of the profile which suggests changes in the emissivity of the inner accretion flow. Dramatic but localized profile changes are observed during flares and high-states of broad-line flux. In 3C 332, these changes can be explained by a slow, smooth, secular change in disk illumination. In Arp 102B and 3C 390.3, however, a simple disk model cannot explain the asymmetric profile changes, suggesting a need for more sophisticated models. We also observe sharp, transient features that appear in the blue peak of the objects, which require a wellorganized velocity field.

The Astrophysical Journal Supplement Series, 2010

An increasing number of Active Galactic Nuclei (AGNs) exhibit broad, doublepeaked Balmer emission... more An increasing number of Active Galactic Nuclei (AGNs) exhibit broad, doublepeaked 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 have been monitored for nearly a decade in order to observe long-term variations in the profiles of the double-peaked Balmer lines. Variations generally occur on timescales of years, and are attributed to physical changes in the accretion disk. Here we characterize the variability of a subset of seven double-peaked emitters in a model independent way. We find that variability is caused primarily by the presence of one or more discrete "lumps" of excess emission; over a timescale of a year (and sometimes less) these lumps change in amplitude and shape, but the projected velocity of these lumps changes over much longer timescales (several years). We also find that all of the objects exhibit red peaks that are stronger than the blue peak at some epochs and/or blueshifts in the overall profile, contrary to the expectations for a simple, circular accretion disk model, thus emphasizing the need for asymmetries in the accretion disk. Comparisons with two simple models, an elliptical accretion disk and a circular disk with a spiral arm, are unable to reproduce all aspects of the observed variability, although both account for some of the observed behaviors. Three of the seven objects have robust estimates of the black hole masses. For these objects the observed variability timescale is consistent with the expected precession timescale for a spiral arm, but incompatible with that of

Cornell University - arXiv, Aug 21, 2001

In recent surveys of Radio-loud AGN, a new sub-class of objects, known as Weak-Line Radio Galaxie... more In 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 flatter spectra than broad-line and narrow-line radio galaxies. In these respects, WLRGs are reminiscent of Low Ionization Nuclear Emission Regions (LINERs). We have begun a multi-wavelength study of WLRGs to better understand their possible connection to LINERs and the structure of the accretion flow in both these systems. Here, we present new optical spectra of a sample of WLRGs. We find that 81% of the objects have optical emission-line properties that are similar to LINERs, indicating that these two classes of AGN may be related. Future high resolution X-ray observations of WLRGs will be critical in determining the true nature of the accretion flow in these objects.

Bulletin of the American Astronomical Society, Dec 1, 2004

An increasing number of AGNs exhibit broad, double-peaked Balmer emission lines, which are though... more An 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 years. The variability is not a reverberation effect; it is a manifestation of physical changes in the disk. Our group has monitored a set of 20 double-peaked emitters for the past 8 years (longer for some objects). Here, we characterize the variability of the double-peaked Hα line profiles in five objects from our sample. By experimenting with simple models, we find that disks with a single precessing spiral arm are able to reproduce many of the variability trends that are seen in the data.

Noao Proposal, Feb 1, 2007

The XMM Slew Survey is projected to cover 80% of the sky in the soft (0.5--2 keV) and hard (2--10... more The XMM Slew Survey is projected to cover 80% of the sky in the soft (0.5--2 keV) and hard (2--10 keV) bands. The survey has a flux limit of 4 × 10-12 erg s-1 cm-2 in the hard band. Like all hard-band surveys, it has the ability to detect even heavily absorbed AGN, and the large area coverage makes it

An increasing number of active galactic nuclei (AGN) exhibit broad, double-peaked Balmer emission... more An increasing number of active galactic nuclei (AGN) exhibit broad, double-peaked Balmer emission lines that originate in the outer accretion disk of the AGN. The line profiles have been observed to vary on timescales of several months to years. Over the past decade, our group has monitored a set of 20 double-peaked emitters. Here we characterize the variability patterns of

The Swift Gamma-Ray Burst satellite has detected a largely unbiased towards absorption sample of ... more The Swift Gamma-Ray Burst satellite has detected a largely unbiased towards absorption sample of local (< z >≈ 0.03) AGN, based solely on their 14-195 keV flux. In the first 9 months of the survey, 153 AGN sources were detected. The X-ray properties in the 0.3-10 keV band have been compiled and presented based on analyses with XMM-Newton, Chandra, Suzaku, and the Swift XRT (Winter et al. 2009). Additionally, we have compiled a sub-sample of sources with medium resolution optical ground-based spectra from the SDSS or our own observations at KPNO. In this sample of 60 sources, we have classified the sources using standard emission line diagnostic plots, obtained masses for the broad line sources through measurement of the broad Hβ emission line, and measured the [OIII] 5007Å luminosity of this sample. Based on continuum fits to the intrinsic absorption features, we have obtained clues about the stellar populations of the host galaxies. We now present the highlights of our X-ray and optical studies of this unique sample of local AGNs, including a comparison of the 2-10 keV and 14-195 keV X-ray luminosities with the [OIII] 5007Å luminosity and the implications of our results towards measurements of bolometric luminosities.

The Swift Burst Alert Telescope (BAT), while not focused on a Gamma-ray burst, conducts an all-sk... more The Swift Burst Alert Telescope (BAT), while not focused on a Gamma-ray burst, conducts an all-sky survey in the 14 - 195 keV band. After the first 9 months, the BAT has detected a sample of 153 local (z 0.03) AGN at a flux limit of a few times 10-11 erg/s/cm-2 (Tueller et al. 2007). Since the AGN were detected

We present new results from a 40.8 ks Chandra ACIS observation of the young supernova remnant (SN... more We present new results from a 40.8 ks Chandra ACIS observation of the young supernova remnant (SNR) N103B located in the Large Magellanic Cloud. The high resolution Chandra image reveals structure at the sub-arcsecond level, including several bright knots and filaments. Narrow-band imaging and spatially resolved spectroscopy reveal dramatic spectral variations in this remnant as well. In this paper we

We present the results of a simultaneous XMM-Newton and RXTE observation of the Broad-Line Radio ... more We present the results of a simultaneous XMM-Newton and RXTE observation 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 K alpha line. When fit with a Gaussian emission line, the feature has an equivalent width of 60±20 eV and

The Astrophysical Journal, 2005

We present the results of simultaneous XMM-Newton and RXTE observations of the Broad-Line Radio G... more We 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 Kα emission line region. When fitted with a Gaussian emission line, the feature has an equivalent width of 40-100 eV and full-width at half maximum of greater than 20,000 km s −1 , however the exact properties of this weak line are highly dependent upon the chosen continuum model. The width of the line suggests an origin in the inner accretion disk, which is, however, inconsistent with the lack of Compton reflection. We find that much of the broad residual emission can be attributed to continuum curvature. The data are consistent with a model in which the primary powerlaw continuum is reprocessed by an accretion disk which is truncated as small radii. Alternatively, the primary source could be partially covered by a dense absorber. The latter model is less attractive than the former because of the small inclination angle of the jet of 3C 111 to the line of sight. We consider it likely that the curved continuum of the partial covering model is fortuitously similar to the continuum shape of the reprocessing model. In both models, the fit is greatly improved by the addition of an unresolved Fe Kα emission line, which could arise either in a Compton-thin obscuring torus or dense clouds lying along the line of sight. We also find that there are unacceptable residuals at low energies in the MOS data in particular, which were modeled as a Gaussian with an energy of ∼ 1.5 keV; we attribute these residuals to calibration uncertainties of the MOS detectors.

The Astrophysical Journal, 2010

The Swift Burst Alert Telescope (BAT) survey of Active Galactic Nuclei (AGN) is providing an unpr... more The Swift Burst Alert Telescope (BAT) survey of Active Galactic Nuclei (AGN) is providing an unprecedented view of local AGNs (< z >≈ 0.03) and their host galaxy properties. In this paper, we present an analysis of the optical spectra of a sample of 64 AGNs from the 9-month survey, detected solely based on their 14-195 keV flux. Our analysis includes both archived spectra from the Sloan Digital Sky Survey and our own observations from the 2.1-m Kitt Peak National Observatory telescope. Among our results, we include line ratio classifications utilizing standard emission line diagnostic plots, [O III] 5007Å luminosities, and Hβ derived black hole masses. As in our Xray study, we find the type 2 sources to be less luminous (in [O III] 5007Å and 14-195 keV luminosities) with lower accretion rates than the type 1 sources. We find that the optically classified LINERs, H II/composite galaxies, and ambiguous sources have the lowest luminosities, while both broad line and narrow line Seyferts have similar luminosities. From a comparison of the hard X-ray (14-195 keV) and [O III] luminosities, we find that both the observed and extinction-corrected [O III] luminosities are weakly correlated with X-ray luminosity. In a study of the host galaxy properties from both continuum fits and measurements of the stellar absorption indices, we find that the hosts of the narrow line sources have properties consistent with late type galaxies.

The Astrophysical Journal, 2009

We present XMM-Newton and Suzaku observations of the broad-line radio galaxy 3C 390.3 acquired in... more We present XMM-Newton and Suzaku observations of the broad-line radio galaxy 3C 390.3 acquired in 2004 October and 2006 December, respectively. An archival Swift BAT spectrum from the 9 month survey is also analyzed, as well as an optical spectrum simultaneous to XMM-Newton. At soft X-rays, no absorption features are detected in the Reflection Grating Spectrometer spectrum of 3C 390.3; a narrow emission line is found at 0.564 keV, most likely originating in the narrow-line region. Both the EPIC and XIS data sets confirm the presence of an Fe Kα emission line at 6.4 keV with equivalent width (EW) = 40 eV. The Fe Kα line has a width FWHM ∼ 8800 km s −1 , consistent within a factor of 2 with the width of the double-peaked Hα line, suggesting an origin from the broad-line region. The data show for the first time a weak, broad bump extending from 5 to 7 keV. When fitted with a Gaussian, its centroid energy is 6.6 keV in the source's rest frame with FWHM of 43,000 km s −1 and EW of 50 eV; its most likely interpretation is emission from He-like Fe (Fe xxv), suggesting the presence of an ionized medium in the inner regions of 3C 390.3. The broadband 0.5-100 keV continuum is well described by a single power law with photon index Γ = 1.6 and cutoff energy 157 keV, plus cold reflection with strength R = 0.5. In addition, ionized reflection is required to account for the 6.6 keV bump in the broadband continuum, yielding an ionization parameter ξ ∼ 2700 erg cm s −1 ; the inner radius of the ionized reflector is constrained to be larger than 20r G , although this result depends on the assumed emissivity profile of the disk. If true, we argue that the lack of broad Fe K emission from within 20r G indicates that the innermost regions of the disk in 3C 390.3 are obscured and/or poorly illuminated. While the spectral energy distribution (SED) of 3C 390.3 is generally dominated by accretionrelated continuum, during accretion low states the jet can significantly contribute in the optical to X-ray bands via synchrotron self-Compton emission. The Compton component is expected to extend to and peak at GeV gamma rays where it will be detected with the Fermi Gamma-Ray Space Telescope during its first few years of operation.

The Astrophysical Journal, 2003

We report on the results from a Chandra ACIS observation of the young, compact, supernova remnant... more We report on the results from a Chandra ACIS observation of the young, compact, supernova remnant N103B. The unprecedented spatial resolution of Chandra reveals sub-arcsecond structure, both in the brightness and in spectral variations. Underlying these small-scale variations is a surprisingly simple radial structure in the equivalent widths of the strong Si and S emission lines. We investigate these radial variations through spatially resolved spectroscopy using a plane-parallel, non-equilibrium ionization model with multiple components. The majority of the emission arises from components with a temperature of 1 keV: a fully ionized hydrogen component; a high ionization timescale (n e t> 10 12 s cm −3) component containing Si, S, Ar, Ca, and Fe; and a low ionization timescale (n e t∼10 11 s cm −3) O, Ne, and Mg component. To reproduce the strong Fe Kα line, it is necessary to include additional Fe in a hot (> 2 keV), low ionization (n e t∼10 10.8 s cm −3) component. This hot Fe may be in the form of hot Fe bubbles, formed in the radioactive decay of clumps of 56 Ni. We find no radial variation in the ionization timescales or temperatures of the various components. Rather, the Si and S equivalent widths increase at large radii because these lines, as well as those of Ar and Ca, are formed in a shell occupying the outer half of the remnant. A shell of hot Fe is located interior to this, but there is a large region of overlap between these two shells. In the inner 30% of the remnant, there is a core of cooler, 1 keV Fe. We find that the distribution of the ejecta and the yields of the intermediate mass species are consistent with model prediction for Type Ia events.

The Astrophysical Journal, 2003

A handful of well-studied Weak-Line Radio Galaxies (WLRGs) have been traditionally classified as ... more A handful of well-studied Weak-Line Radio Galaxies (WLRGs) have been traditionally classified as Low Ionization Nuclear Emission-line Regions (LIN-ERs), suggesting that these two groups of AGNs might be related. In this paper, we present new optical emission-line measurements for twenty Weak-Line Radio Galaxies which we supplement with measurements for an additional four from the literature. Classifying these objects by their emission-line ratios, we find that 50% of the objects are robustly classified as LINERs while an additional 25% are likely to be LINERs. Photoionization calculations show that the Spectral Energy Distribution of the well-studied WLRG 3C 270 (NGC 4261) is able to produce the observed emission-line ratios, but only if the UV emission seen by the narrow emission-line gas is significantly higher than that observed, implying A V = 2.5-4.2 magnitudes along our line of sight to the nucleus. From the photoionization calculations, we find that the emission-line gas must have an ionization parameter between 10 −3.5 and 10 −4.0 and a wide range in hydrogen density (10 2-10 6 cm −3) to reproduce the measured emission-line ratios, similar to the properties inferred for the emission-line gas in LINERs. Thus, we find that properties of the emission-line gas as well as the underlying excitation mechanism are indeed similar in LINERs and WLRGs. By extension, the central engines of accretionpowered LINERs and WLRGs, which do host an accreting black hole, may be qualitatively similar.

The Astrophysical Journal, 2006

We have obtained near-IR spectra of five Active Galactic Nuclei that exhibit double-peaked Balmer... more We 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 from the Ca ii λλ8494, 8542, 8662Å absorption lines and were found to range from 140 to 200 km s −1. Using the well-known correlation between the black hole mass and the stellar velocity dispersion, the black hole masses in these galaxies were estimated to range from 4 × 10 7 to 1.2 × 10 8 M ⊙. We supplement the observations presented here with estimates of the black holes masses for five additional double-peaked emitters (Arp 102B, 3C 390.3, NGC 4579, NGC 4203, and M81) obtained by other authors using similar methods. Using these black hole masses, we infer the ratio of the bolometric luminosity to the Eddington luminosity, (L bol /L Edd). We find that two objects (Pictor A and PKS 0921-213) have L bol /L Edd ∼ 0.2, whereas the other objects have L bol /L Edd 10 −2 (nearby, low-luminosity double-peaked emitters are the most extreme, with L bol /L Edd 10 −4). The physical time scales in the outer regions of the accretion disks (at r ∼ 10 3 GM/c 2) in these objects were also estimated and range from a few months, for the dynamical time scale, to several decades for the sound crossing time scale. The profile variability in these objects are typically an order of magnitude longer than the dynamical time, but we note that variability occurring on the dynamical time scale has not been ruled out by the observations.

The Astronomical Journal, 2011

We present the results from exploratory (12-23 ks) XMM-Newton observations of six optically selec... more We present the results from exploratory (12-23 ks) XMM-Newton observations of six optically selected, radio-loud active galactic nuclei (AGNs), together with new radio data and a reanalysis of their archival SDSS spectra. The sources were selected in an effort to expand the current sample of radio-loud AGNs suitable for detailed X-ray spectroscopy studies. The sample includes three broad-line and three

New Astronomy Reviews, 2009

Broad, double-peaked, Balmer emission lines are found in the optical spectra of a relatively smal... more Broad, double-peaked, Balmer emission lines are found in the optical spectra of a relatively small fraction of active galactic nuclei. They can be an extremely useful diagnostic for the structure and dynamics of the ''broad-line region" (the medium that emits the broad emission lines). In general terms the rarity and shapes of their profiles provide strong constraints on universal models of the broad-line region. A series of observational tests and basic physical considerations suggest that these lines are emitted from a flat, rotating disk, very likely the outer parts of the accretion disk that fuels the black hole. In the context of models for accretion disk winds, double-peaked emission lines originate in disks with feeble winds of low optical depth. Therefore, they provide evidence that the outer accretion disk and its associated wind are the source of the broad emission lines. Within this framework, double-peaked Balmer emission lines and corresponding high-ionization lines in the near-ultraviolet allow us to study the conditions under which the winds become dense and the onset of significant outflows. Moreover, double-peaked emission lines give us a direct view of the dense material of the disk proper and allow us to study dynamical perturbations and other transient behavior though the long-term variability of their profiles.

The Astrophysical Journal Supplement Series, 2007

We present up to two decades of spectroscopic monitoring of the double-peaked broad Hα emission l... more We present up to two decades of spectroscopic monitoring of the double-peaked broad Hα 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 disk, and their profiles vary on timescales of months to years. This variability is a valuable probe for understanding the structure and dynamics of the accretion disk. We characterize the long-term broad-line profile variability in detail, and compare the evolution of the line profiles with predictions from a few simple physical models for dynamical processes in the accretion disk. We find no evidence for persistent, periodic variability that would be indicative of a precessing elliptical disk, or a circular disk with a long-lived, single-armed spiral or warp. We do find transient, periodic variability on the orbital timescale, possibly resulting from shocks induced by tidal perturbations, and variability in the wings of the profile which suggests changes in the emissivity of the inner accretion flow. Dramatic but localized profile changes are observed during flares and high-states of broad-line flux. In 3C 332, these changes can be explained by a slow, smooth, secular change in disk illumination. In Arp 102B and 3C 390.3, however, a simple disk model cannot explain the asymmetric profile changes, suggesting a need for more sophisticated models. We also observe sharp, transient features that appear in the blue peak of the objects, which require a wellorganized velocity field.

The Astrophysical Journal Supplement Series, 2010

An increasing number of Active Galactic Nuclei (AGNs) exhibit broad, doublepeaked Balmer emission... more An increasing number of Active Galactic Nuclei (AGNs) exhibit broad, doublepeaked 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 have been monitored for nearly a decade in order to observe long-term variations in the profiles of the double-peaked Balmer lines. Variations generally occur on timescales of years, and are attributed to physical changes in the accretion disk. Here we characterize the variability of a subset of seven double-peaked emitters in a model independent way. We find that variability is caused primarily by the presence of one or more discrete "lumps" of excess emission; over a timescale of a year (and sometimes less) these lumps change in amplitude and shape, but the projected velocity of these lumps changes over much longer timescales (several years). We also find that all of the objects exhibit red peaks that are stronger than the blue peak at some epochs and/or blueshifts in the overall profile, contrary to the expectations for a simple, circular accretion disk model, thus emphasizing the need for asymmetries in the accretion disk. Comparisons with two simple models, an elliptical accretion disk and a circular disk with a spiral arm, are unable to reproduce all aspects of the observed variability, although both account for some of the observed behaviors. Three of the seven objects have robust estimates of the black hole masses. For these objects the observed variability timescale is consistent with the expected precession timescale for a spiral arm, but incompatible with that of