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University of Nebraska - Lincoln

Martin Gaskell Publications

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Full-Text Articles in Physics

Setting Ubvri Photometric Zero-Points Using Sloan Digital Sky Survey Ugriz Magnitudes, Taylor S. Chonis, C. Martin Gaskell Jan 2008

Setting Ubvri Photometric Zero-Points Using Sloan Digital Sky Survey Ugriz Magnitudes, Taylor S. Chonis, C. Martin Gaskell

Martin Gaskell Publications

We discuss the use of Sloan Digital Sky Survey (SDSS) ugriz point-spread function (PSF) photometry for setting the zero points of UBVRI CCD images. From a comparison with the Landolt (1992, AJ, 104, 340) standards and our own photometry we find that there is a fairly abrupt change in B, V, R, and I zero points around g, r, i ∼ 14.5, and in the U zero point at u ∼ 16. These changes correspond to where there is significant interpolation due to saturation in the SDSS PSF fluxes. There also seems to be another, much smaller systematic effect for stars ...


Agn Reddening And Ultraviolet Extinction Curves From Hubble Space Telescope Spectra, C. Martin Gaskell, C. Martin Gaskell Nov 2007

Agn Reddening And Ultraviolet Extinction Curves From Hubble Space Telescope Spectra, C. Martin Gaskell, C. Martin Gaskell

Martin Gaskell Publications

We present intrinsic extinction curves for 14 AGNs. The AGNs have reddenings, E(B-V), of up to 0.36 mag. The majority (13 out of 14) of the extinction curves are not steep in the UV. Of the seven best determined extinction curves, five have extinction curves that are as flat as the standard Galactic curve in the optical and near UV, but flatter in the far UV, and without the λ2175 feature. One AGN, B3 0754+394, has a steep SMC-like extinction curve, and another, Mrk 304, has an LMC-like extinction curve, including a probable λ2175 bump. The remaining ...


Discovery Of Polarization Reverberation In Ngc 4151, C. Martin Gaskell, René W. Goosmann, Nelly I. Merkulova, Nikolay M. Shakhovskoy, Masatoshi Shoji Nov 2007

Discovery Of Polarization Reverberation In Ngc 4151, C. Martin Gaskell, René W. Goosmann, Nelly I. Merkulova, Nikolay M. Shakhovskoy, Masatoshi Shoji

Martin Gaskell Publications

Observations of the optical polarization of NGC 4151 in 1997–2003 show variations of an order of magnitude in the polarized flux while the polarization position angle remains constant. The amplitude of variability of the polarized flux is comparable to the amplitude of variability of the total U-band flux, except that the polarized flux follows the total flux with a lag of 8±3 days. The time lag and the constancy of the position angle strongly favor a scattering origin for the variable polarization rather than a non-thermal synchrotron origin. The orientation of the position angle of the polarized flux ...


The Case For Optically Thick High-Velocity Broad-Line Region Gas In Active Galactic Nuclei, Stephanie A. Snedden, C. Martin Gaskell Nov 2007

The Case For Optically Thick High-Velocity Broad-Line Region Gas In Active Galactic Nuclei, Stephanie A. Snedden, C. Martin Gaskell

Martin Gaskell Publications

A combined analysis of the profiles of the main broad quasar emission lines in both Hubble Space Telescope and optical spectra shows that while the profiles of the strong UV lines are quite similar, there is frequently a strong increase in the Lyα/Hα ratio in the high-velocity gas.We show that the suggestion that the high-velocity gas is optically thin presents many problems.We show that the relative strengths of the high-velocity wings arise naturally in an optically thick BLR component. An optically thick model successfully explains the equivalent widths of the lines, the Lyα/Hα ratios and flatter ...


Transformations Between 2mass, Sdss And Bvri Photometric Systems: Bridging The Near Infrared And Optical, S. Bilir, S. Ak, S. Karaali, A. Cabrera-Lavers, T. S. Chonis, C. Martin Gaskell Nov 2007

Transformations Between 2mass, Sdss And Bvri Photometric Systems: Bridging The Near Infrared And Optical, S. Bilir, S. Ak, S. Karaali, A. Cabrera-Lavers, T. S. Chonis, C. Martin Gaskell

Martin Gaskell Publications

We present color transformations for the conversion of the 2MASS photometric system to the Johnson-Cousins UBV RI system and further into the SDSS ugriz system. We have taken SDSS gri magnitudes of stars measured with the 2.5-m telescope from SDSS Data Release 5 (DR5), and BV RI and JHKs magnitudes from Stetson’s catalogue and Cutri et al. (2003), respectively. We matched thousands of stars in the three photometric systems by their coordinates and obtained a homogeneous sample of 825 stars by the following constraints, which are not used in previous transformations: 1) the data are de-reddened, 2 ...


Ngc 5548: The Agn Energy Budget Problem And The Geometry Of The Broad-Line Region And Torus, C. Martin Gaskell, Elizabeth S. Klimek, Ludmila S. Nazarova Nov 2007

Ngc 5548: The Agn Energy Budget Problem And The Geometry Of The Broad-Line Region And Torus, C. Martin Gaskell, Elizabeth S. Klimek, Ludmila S. Nazarova

Martin Gaskell Publications

We consider in detail the spectral energy distribution (SED) and multi-wavelength variability of NGC 5548. Comparison with the SEDs of other AGNs implies that the internal reddening of NGC 5548 is E(B-V) = 0.17 mag. The extinction curve is consistent with the mean curve of other AGNs found by Gaskell & Benker, but inconsistent with an SMC-type reddening curve. Because most IR emission originates exterior to the broad-line region (BLR), the SED seen by the inner BLR is different from that seen by the outer BLR and from the earth. The most likely BLR covering factor is ~ 40% and it ...


Modeling Optical And Uv Polarization Of Agns I. Imprints Of Individual Scattering Regions, René W. Goosmann, C. Martin Gaskell Oct 2007

Modeling Optical And Uv Polarization Of Agns I. Imprints Of Individual Scattering Regions, René W. Goosmann, C. Martin Gaskell

Martin Gaskell Publications

Context. Spectropolarimetry of AGNs is a powerful tool for studying the structure and kinematics of the inner regions of quasars. Aims. We wish to investigate the effects of various AGN scattering region geometries on the polarized flux. Methods. We introduce a new, publicly available Monte Carlo radiative transfer code, STOKES, which models polarization induced by scattering off free electrons and dust grains. We model a variety of regions in AGNs. Results. We find that the shape of the funnel of the dusty torus has a significant impact on the polarization efficiency. A compact torus with a steep inner surface scatters ...


Setting Ubvri Photometric Zero-Points Using Sloan Digital Sky Survey Ugriz Magnitudes, Taylor S. Chonis, C. Martin Gaskell Oct 2007

Setting Ubvri Photometric Zero-Points Using Sloan Digital Sky Survey Ugriz Magnitudes, Taylor S. Chonis, C. Martin Gaskell

Martin Gaskell Publications

We discuss the use of Sloan Digital Sky Survey (SDSS) ugriz point-spread function (PSF) photometry for setting the zero points of UBVRI CCD images. From a comparison with the Landolt (1992) standards and our own photometry we find that there is a fairly abrupt change in B, V, R, & I zero points around g, r, i ~ 14.5, and in the U zero point at u ~ 16. These changes correspond to where there is significant interpolation due to saturation in the SDSS PSF fluxes. There also seems to be another, much smaller systematic effect for stars with g,r ≥ 19 ...


X-Ray/Ultraviolet Observing Campaign Of The Markarian 279 Active Galactic Nucleus Outflow: A Close Look At The Absorbing/Emitting Gas With Chandra-Letgs, E. Costantini, Jelle S. Kaastra, Nahum Arav, Gerard A. Kriss, K. C. Steenbrugge, Jack R. Gabel, F. Verbunt, Ehud Behar, C. Martin Gaskell, Kirk T. Korista, Daniel Proga, Jessica Kim-Quijano, J. E. Scott, Elizabeth S. Klimek, C. H. Hedrick Sep 2007

X-Ray/Ultraviolet Observing Campaign Of The Markarian 279 Active Galactic Nucleus Outflow: A Close Look At The Absorbing/Emitting Gas With Chandra-Letgs, E. Costantini, Jelle S. Kaastra, Nahum Arav, Gerard A. Kriss, K. C. Steenbrugge, Jack R. Gabel, F. Verbunt, Ehud Behar, C. Martin Gaskell, Kirk T. Korista, Daniel Proga, Jessica Kim-Quijano, J. E. Scott, Elizabeth S. Klimek, C. H. Hedrick

Martin Gaskell Publications

We present a Chandra-LETGS observation of the Seyfert 1 galaxy Mrk 279. This observation was carried out simultaneously with HST-STIS and FUSE, in the context of a multi-wavelength study of this source. The Chandra pointings were spread over ten days for a total exposure time of ~360 ks. The maximal continuum flux variation is of the order of 30%. The spectrum of Mrk 279 shows evidence of broad emission features, especially at the wavelength of the OVII triplet. We quantitatively explore the possibility that this emission is produced in the broad line region (BLR). We modeled the broad UV ...


Chemical Abundances In An Agn Environment: X-Ray/Uv Campaign On The Markarian 279 Outflow, Nahum Arav, Jack R. Gabel, Kirk T. Korrista, Jelle S. Kaastra, Gerard A. Kriss, Ehud Behar, Elisa Constantini, C. Martin Gaskell, Ari Laor, C. Nalaka Kodituwakku, Daniel Proga, Masao Sako, Jennifer E. Scott, Katrien C. Steenbrugge Apr 2007

Chemical Abundances In An Agn Environment: X-Ray/Uv Campaign On The Markarian 279 Outflow, Nahum Arav, Jack R. Gabel, Kirk T. Korrista, Jelle S. Kaastra, Gerard A. Kriss, Ehud Behar, Elisa Constantini, C. Martin Gaskell, Ari Laor, C. Nalaka Kodituwakku, Daniel Proga, Masao Sako, Jennifer E. Scott, Katrien C. Steenbrugge

Martin Gaskell Publications

We present the first reliable determination of chemical abundances in an active galactic nucleus (AGN) outflow. The abundances are extracted from the deep and simultaneous Far Ultraviolet Spectroscopic Explorer (FUSE) and Hubble Space Telescope (HST ) STIS observations of Mrk 279. This data set is exceptional for its high signal-to-noise ratio, unblended doublet troughs, and little Galactic absorption contamination. These attributes allow us to solve for the velocity-dependent covering fraction and therefore obtain reliable column densities for many ionic species. For the first time, we have enough such column densities to simultaneously determine the ionization equilibrium and abundances in the flow ...


Hubble Space Telescope Ultraviolet Spectroscopy Of 14 Low-Redshift Quasars, Rajib Ganguly, Michael S. Brotherton, Nahum Arav, Sara R. Heap, Lutz Wisotzki, Thomas L. Aldcroft, Danielle Alloin, Ehud Behar, Gabriela Canalizo, D. Michael Crenshaw, Martijn De Kool, Kenneth Chambers, Gerald Cecil, Eleni Chatzichristou, John Everett, Jack R. Gabel, C. Martin Gaskell, Emmanuel Galliano, Richard F. Green, Patrick B. Hall, Dean C. Hines, Vesa T. Junkkarinen, Jelle S. Kaastra, Mary Elizabeth Kaiser, Demosthenes Kazanas, Arieh Konigl, Kirk T. Korista, Gerard A. Kriss, Ari Laor, Karen M. Leighly, Smita Mathur, Patrick Ogle, Daniel Proga, Bassem Sabra, Ran Sivron, Stephanie A. Snedden, Randal Telfer, Marianne Vestergaard Feb 2007

Hubble Space Telescope Ultraviolet Spectroscopy Of 14 Low-Redshift Quasars, Rajib Ganguly, Michael S. Brotherton, Nahum Arav, Sara R. Heap, Lutz Wisotzki, Thomas L. Aldcroft, Danielle Alloin, Ehud Behar, Gabriela Canalizo, D. Michael Crenshaw, Martijn De Kool, Kenneth Chambers, Gerald Cecil, Eleni Chatzichristou, John Everett, Jack R. Gabel, C. Martin Gaskell, Emmanuel Galliano, Richard F. Green, Patrick B. Hall, Dean C. Hines, Vesa T. Junkkarinen, Jelle S. Kaastra, Mary Elizabeth Kaiser, Demosthenes Kazanas, Arieh Konigl, Kirk T. Korista, Gerard A. Kriss, Ari Laor, Karen M. Leighly, Smita Mathur, Patrick Ogle, Daniel Proga, Bassem Sabra, Ran Sivron, Stephanie A. Snedden, Randal Telfer, Marianne Vestergaard

Martin Gaskell Publications

We present low-resolution ultraviolet spectra of 14 low-redshift (zem ≤ 0:8) quasars observed with the Hubble Space Telescope STIS as part of a Snapshot project to understand the relationship between quasar outflows and luminosity. By design, all observations cover the C iv emission line. Ten of the quasars are from the Hamburg-ESO catalog, three are from the Palomar-Green catalog, and one is from the Parkes catalog. The sample contains a few interesting quasars, including two broad absorption line (BAL) quasars (HE 0143-3535 and HE 0436-2614), one quasar with a mini-BAL (HE 1105-0746), and one quasar with associated narrow absorption ...


Agn Polarization Modeling With Stokes, René W. Goosmann, C. Martin Gaskell Jan 2007

Agn Polarization Modeling With Stokes, René W. Goosmann, C. Martin Gaskell

Martin Gaskell Publications

We introduce a new, publicly available Monte Carlo radiative transfer code, STOKES, which has been developed to model polarization induced by scattering off free electrons and dust grains. It can be used in a wide range of astrophysical applications. Here, we apply it to model the polarization produced by the equatorial obscuring and scattering tori assumed to exist in active galactic nuclei (AGNs). We present optical/UV modeling of dusty tori with a curved inner shape and for two different dust types: one composition reproduces extinction properties of our Galaxy, and the other is derived from composite quasar spectra. The ...


Modeling The Polarization Of Dusty Scattering Cones In Active Galactic Nuclei, René W. Goosmann, C. Martin Gaskell, Masatoshi Shoji Jan 2007

Modeling The Polarization Of Dusty Scattering Cones In Active Galactic Nuclei, René W. Goosmann, C. Martin Gaskell, Masatoshi Shoji

Martin Gaskell Publications

We have used the STOKES radiative transfer code, to model polarization induced by dust scattering in the polar regions of Active Galactic Nuclei (AGN). We discuss the wavelength-dependence of the spectral intensity and polarization over the optical/UV range at different viewing angles for two different types of dust: a Galactic dust model, and a dust model inferred from extinction properties of AGN.


Modeling Optical And Uv Polarization Of Agnsi. Imprints Of Individual Scattering Regions, René W. Goosmann, C. Martin Gaskell Jan 2007

Modeling Optical And Uv Polarization Of Agnsi. Imprints Of Individual Scattering Regions, René W. Goosmann, C. Martin Gaskell

Martin Gaskell Publications

Context. Spectropolarimetry of AGNs is a powerful tool for studying the structure and kinematics of the inner regions of quasars. Aims. We wish to investigate the effects of various AGN scattering region geometries on the polarized flux. Methods. We introduce a new, publicly available Monte Carlo radiative transfer code, stokes, which models polarization induced by scattering off free electrons and dust grains. We model a variety of regions in AGNs. Results. We find that the shape of the funnel of the dusty torus has a significant impact on the polarization efficiency. A compact torus with a steep inner surface scatters ...


Optical And X-Ray Variability Of Agns, C. Martin Gaskell Dec 2006

Optical And X-Ray Variability Of Agns, C. Martin Gaskell

Martin Gaskell Publications

I present new comparisons of AGN optical, UV, and X-ray variations. These reveal complex relationships between the different passbands that can change with time in a given object. While there is evidence from several objects that X-ray and optical activity levels are correlated on long timescales, variations on shorter timescales can occur independently. It is proposed that the combination of correlated and uncorrelated short-timescale variability is a consequence of anisotropic high-energy emission. It is also argued that the correlation between X-ray and optical variability on long timescales must be due to a common underlying factor and not to reprocessing of ...


Optical Variability Of The Three Brightest Nearby Quasars, C. Martin Gaskell, Andrew J. Benker, Jeffrey S. Campbell, Thomas A. George, Cecilia H. Hedrick, Mary E. Hiller, Elizabeth S. Klimek, Joseph P. Leonard, Shoji Masatoshi, Bradley W. Peterson, Kelly S. Peterson, Kelly M. Sanders Dec 2006

Optical Variability Of The Three Brightest Nearby Quasars, C. Martin Gaskell, Andrew J. Benker, Jeffrey S. Campbell, Thomas A. George, Cecilia H. Hedrick, Mary E. Hiller, Elizabeth S. Klimek, Joseph P. Leonard, Shoji Masatoshi, Bradley W. Peterson, Kelly S. Peterson, Kelly M. Sanders

Martin Gaskell Publications

We report on the relative optical variability of the three brightest nearby quasars, 3C 273, PDS 456, and PHL 1811. All three have comparable absolute magnitudes, but PDS 456 and PHL 1811 are radio quiet. PDS 456 is a broadline object, but PHL 1811 could be classified as a high-luminosity Narrow-Line Seyfert 1 (NLS1). Both of the radio-quiet quasars show significant variability on a timescale of a few days. The seasonal rms V-band variability amplitudes of 3C 273 and PDS 456 are indistinguishable, and the seasonal rms variability amplitude of PHL 1811 was only exceeded by 3C 273 once in ...


The Origin Of Wavelength-Dependent Continuum Delays In Agns – A New Model, C. Martin Gaskell Dec 2006

The Origin Of Wavelength-Dependent Continuum Delays In Agns – A New Model, C. Martin Gaskell

Martin Gaskell Publications

A model of wavelength-dependent lags in optical continuum variability of AGNs is proposed which avoids the problems of the popular “lamppost” model. Rather than being due to reprocessing of high-energy radiation from a hypothetical source above the accretion disk, the wavelength-dependent delays observed from the B to I bands are instead due to contamination of an intrinsically coherently variable continuum with the Wien tail of the thermal emission from the hot dust in the surrounding torus. The new model correctly gives the size, wavelength dependence, and luminosity dependence of the lags, and quantitatively predicts observed color hysteresis. The model also ...


Evidence For Two Kinematically Distinct Broad Emission Line Producing Regions In Active Galactic Nuclei, Stephanie A. Snedden, C. Martin Gaskell Nov 2006

Evidence For Two Kinematically Distinct Broad Emission Line Producing Regions In Active Galactic Nuclei, Stephanie A. Snedden, C. Martin Gaskell

Martin Gaskell Publications

We present the results of an analysis of line profiles of high- and low-ionization broad emission lines in 8 AGNs observed by the Hubble Space Telescope. We derive the physical conditions in the gas as a function of velocity. We find no evidence for a separate intermediate line region. For the broad line region as a whole we find a major contradiction between the velocity dependencies of conditions deduced from the major high-ionization lines and those deduced from the hydrogen lines alone if they are assumed to come from the same gas clouds. The hydrogen lines imply that the density ...


X-Ray/Ultraviolet Observing Campaign Of The Markarian 279 Active Galactic Nucleus Outflow: A Close Look At The Absorbing/Emitting Gas With Chandra-Letgs, E. Constantini, Jelle S. Kaastra, Nahum Arav, Gerard A. Kriss, K.C. Steenbrugge, Jack R. Gabel, F. Verbunt, Ehud Behar, C. Martin Gaskell, Kirk T. Korista, Daniel Proga, Jessica Kim-Quijano, J.E. Scott, Elizabeth S. Klimek, C.H. Hedrick Nov 2006

X-Ray/Ultraviolet Observing Campaign Of The Markarian 279 Active Galactic Nucleus Outflow: A Close Look At The Absorbing/Emitting Gas With Chandra-Letgs, E. Constantini, Jelle S. Kaastra, Nahum Arav, Gerard A. Kriss, K.C. Steenbrugge, Jack R. Gabel, F. Verbunt, Ehud Behar, C. Martin Gaskell, Kirk T. Korista, Daniel Proga, Jessica Kim-Quijano, J.E. Scott, Elizabeth S. Klimek, C.H. Hedrick

Martin Gaskell Publications

We present a Chandra-LETGS observation of the Seyfert 1 galaxy Mrk 279. This observation was carried out simultaneously with HST-STIS and FUSE, in the context of a multiwavelength study of this source. The Chandra pointings were spread over ten days for a total exposure time of ~360 ks. The maximal continuum flux variation is of the order of 30%. The spectrum of Mrk 279 shows evidence of broad emission features, especially at the wavelength of the O VII triplet. We quantitatively explore the possibility that this emission is produced in the broad line region (BLR). We modeled the broad ...


Hubble Space Telescope Ultraviolet Spectroscopy Of Fourteen Low-Redshift Quasars, Rajib Ganguly, Michael S. Brotherton, Nahum Arav, Sara R. Heap, Lutz Wisotzki, Thomas L. Aldcroft, Danielle Alloin, Ehud Behar, Gabriela Canalizo, D. Michael Crenshaw, Martijn De Kool, Kenneth Chambers, Gerald Cecil, Eleni Chatzichristou, John Everett, Jack R. Gabel, C. Martin Gaskell, Emmanuel Galliano, Richard F. Green, Patrick B. Hall, Dean C. Hines, Vesa T. Junkkarinen, Jelle S. Kaastra, Mary Elizabeth Kaiser, Demosthenes Kazanas, Arieh Konigl, Kirk T. Korista, Gerard A. Kriss, Ari Laor, Karen M. Leighly, Smita Mathur, Patrick Ogle, Daniel Ogle, Bassem Sabra, Ran Sivron, Stephanie A. Snedden, Randal Telfer, Marianne Vestergaard Oct 2006

Hubble Space Telescope Ultraviolet Spectroscopy Of Fourteen Low-Redshift Quasars, Rajib Ganguly, Michael S. Brotherton, Nahum Arav, Sara R. Heap, Lutz Wisotzki, Thomas L. Aldcroft, Danielle Alloin, Ehud Behar, Gabriela Canalizo, D. Michael Crenshaw, Martijn De Kool, Kenneth Chambers, Gerald Cecil, Eleni Chatzichristou, John Everett, Jack R. Gabel, C. Martin Gaskell, Emmanuel Galliano, Richard F. Green, Patrick B. Hall, Dean C. Hines, Vesa T. Junkkarinen, Jelle S. Kaastra, Mary Elizabeth Kaiser, Demosthenes Kazanas, Arieh Konigl, Kirk T. Korista, Gerard A. Kriss, Ari Laor, Karen M. Leighly, Smita Mathur, Patrick Ogle, Daniel Ogle, Bassem Sabra, Ran Sivron, Stephanie A. Snedden, Randal Telfer, Marianne Vestergaard

Martin Gaskell Publications

We present low-resolution ultraviolet spectra of 14 low redshift (z em < 0.8) quasars observed with HST/STIS as part of a Snap project to understand the relationship between quasar outflows and luminosity. By design, all observations cover the C IV emission line. Nine of the quasars are from the Hamburg-ESO catalog, three are from the Palomar-Green catalog, and one is from the Parkes catalog. The sample contains a few interesting quasars including two broad absorption line (BAL) quasars (HE 0143- 3535, HE0436-2614), one quasar with a mini-BAL (HE 1105-0746), and one quasar with associated narrow absorption (HE 0409-5004). These BAL quasars are among the brightest known (though not the most luminous) since they lie at z em< 0.8. We compare the properties of these BAL quasars to the z em < 0.5 Palomar-Green and z em> 1.4 Large Bright Quasar samples. By design, our objects sample luminosities in between these two surveys, and our four absorbed objects are consistent with the υ ∼L 0.62 relation derived by Laor & Brandt (2002). Another quasar, HE0441-2826, contains extremely weak emission lines and our spectrum is consistent with a simple power- law continuum. The quasar is radio-loud, but has a steep spectral index and a lobe- dominated morphology, which argues against it being a blazar. The unusual spectrum of this quasar ...


Different Velocity Dependences Of Physical Conditions Of High- And Low-Ionization Lines In Broad-Line Regions, Stephanie A. Snedden, C. Martin Gaskell Mar 2004

Different Velocity Dependences Of Physical Conditions Of High- And Low-Ionization Lines In Broad-Line Regions, Stephanie A. Snedden, C. Martin Gaskell

Martin Gaskell Publications

We present results from a study of high- and low-ionization emission line ratios as a function of projected velocity for a sample of eight active galactic nuclei (AGNs). Our results are based on analysis of high signal-to-noise optical and Hubble Space Telescope (HST) UV spectra. Comparing the emission line ratios to those predicted by photoionization models indicates that the physical conditions responsible for the high-ionization emission lines are consistent with a wind, whereas those of the low-ionization lines are consistent with a virialized disk.


The Effect Of Abundance Variations On Estimates Of The Densities Of Broad-Line Region Clouds In Quasars, Stephanie A. Snedden, C. Martin Gaskell Aug 1999

The Effect Of Abundance Variations On Estimates Of The Densities Of Broad-Line Region Clouds In Quasars, Stephanie A. Snedden, C. Martin Gaskell

Martin Gaskell Publications

There has been a long-standing discrepancy between the densities deduced from studies of the variability of quasar emission lines and those inferred from standard photoionization analyses. We have found that the higher metal abundances now believed to be present in most quasars lead to the higher densities being predicted by photoionization models. We explain why this is so.


Steps Toward Determination Of The Size And Structure Of The Broad-Line Region In Active Galactic Nuclei. Xiii. Ultraviolet Observations Of The Broad-Line Radio Galaxy 3c 390.3, Paul T. O'Brien, M. Dietrich, K. Leighly, D. Alloin, J. Clavel, D. Michael Crenshaw, K. Horne, G. A. Criss, Julian Henry Krolik, Matthew A. Malkan, Hagai Netzer, Bradley M. Peterson, G. A. Reichert, P. M. Rodriguez-Pascual, W. Wamsteker, K. S.J. Anderson, N. G. Bochkarev, F.-Z. Cheng, A. V. Filippenko, C. Martin Gaskell, I. M. George, M. R. Goad, L. C. Ho, Shai Kaspi, W. Kollatschny, Kirk T. Korista, G. Macalpine, D. Marlow, P. G. Martin, S. L. Morris, Richard William Pogge, B. C. Qian, M. C. Recondo-Gonzalez, J. M. Rodriguez Espinosa, M. Santos-Lleo, A. I. Shapovalova, J. M. Shull, G. M. Stirpe, W.-H. Sun, T. J. Turner, R. Vio, S. Wagner, I. Wanders, K. A. Wills, H. Wu, S. J. Xue, Z.-L. Zou Dec 1998

Steps Toward Determination Of The Size And Structure Of The Broad-Line Region In Active Galactic Nuclei. Xiii. Ultraviolet Observations Of The Broad-Line Radio Galaxy 3c 390.3, Paul T. O'Brien, M. Dietrich, K. Leighly, D. Alloin, J. Clavel, D. Michael Crenshaw, K. Horne, G. A. Criss, Julian Henry Krolik, Matthew A. Malkan, Hagai Netzer, Bradley M. Peterson, G. A. Reichert, P. M. Rodriguez-Pascual, W. Wamsteker, K. S.J. Anderson, N. G. Bochkarev, F.-Z. Cheng, A. V. Filippenko, C. Martin Gaskell, I. M. George, M. R. Goad, L. C. Ho, Shai Kaspi, W. Kollatschny, Kirk T. Korista, G. Macalpine, D. Marlow, P. G. Martin, S. L. Morris, Richard William Pogge, B. C. Qian, M. C. Recondo-Gonzalez, J. M. Rodriguez Espinosa, M. Santos-Lleo, A. I. Shapovalova, J. M. Shull, G. M. Stirpe, W.-H. Sun, T. J. Turner, R. Vio, S. Wagner, I. Wanders, K. A. Wills, H. Wu, S. J. Xue, Z.-L. Zou

Martin Gaskell Publications

As part of an extensive multi-wavelength monitoring campaign, the International Ultraviolet Explorer satellite was used to observe the broad-line radio galaxy 3C 390.3 during the period 1994 December 31-1996 March 5. Spectra were obtained every 6È10 days. The UV continuum varied by a factor of 7 through the campaign, while the broad emission lines varied by factors of 2È5. Unlike previously monitored Seyfert 1 galaxies, in which the X-ray continuum generally varies with a larger amplitude than the UV, in 3C 390.3 the UV continuum light curve is similar in both amplitude and shape to the X-ray light ...


Steps Toward Determination Of The Size And Structure Of The Broad-Line Region In Active Galactic Nuclei. Xiv. Intensive Optical Spectrophotometric Observations Of Ngc 7469, S.J. Collier, Keith Horne, Shai Kaspi, Hagai Netzer, Bradley M. Peterson, I. Wanders, T. Alexander, R. Bertram, A. Comastri, C. Martin Gaskell, Yu. F. Malkov, D. Maoz, M. Mignoli, Richard William Pogge, V.I. Pronik, S.G. Sergeev, Stephanie A. Snedden, G.M. Stirpe, N.G. Bochkarev, A.N. Burenkov, A.I. Shapovalova, R.M. Wagner Jun 1998

Steps Toward Determination Of The Size And Structure Of The Broad-Line Region In Active Galactic Nuclei. Xiv. Intensive Optical Spectrophotometric Observations Of Ngc 7469, S.J. Collier, Keith Horne, Shai Kaspi, Hagai Netzer, Bradley M. Peterson, I. Wanders, T. Alexander, R. Bertram, A. Comastri, C. Martin Gaskell, Yu. F. Malkov, D. Maoz, M. Mignoli, Richard William Pogge, V.I. Pronik, S.G. Sergeev, Stephanie A. Snedden, G.M. Stirpe, N.G. Bochkarev, A.N. Burenkov, A.I. Shapovalova, R.M. Wagner

Martin Gaskell Publications

We present results of an intensive 2 month campaign of ground-based spectrophotometric monitoring of the Seyfert 1 galaxy NGC 7469, with a temporal resolution [approximately less than]1 day. The broad Hα and Hβ emission lines respond to ~35% ultraviolet continuum variations with an amplitude of ~10% and time delays of 5.6±1.3 days and 5.4±0.8 days, respectively. We interpret this as evidence of variable Balmer line gas ~5-6 light days from the central source in this object, widely believed to be a supermassive black hole. The virial mass of the central source implied by ...


Steps Toward Determination Of The Size And Structure Of The Broad-Line Region In Active Galactic Nuclei. Xii. Ground-Based Monitoring Of 3c 390.3, M. Dietrich, Bradley M. Peterson, P. Albrecht, M. Altmann, A.J. Barth, P.J. Bennie, R. Bertram, N.G. Bochkarev, H. Bock, J.M. Braun, A. Burenkov, S. Collier, L.-Z. Fang, O.P. Francis, A. V. Filippenko, C.B. Foltz, W. Gassler, C. Martin Gaskell, M. Geffert, K.K. Ghosh, R.W. Hilditch, R.K. Honeycutt, K. Horne, J.P. Huchra, Shai Kaspi, M. Kummel, K.M. Leighly, D.C. Leonard, Yu. F. Malkov, V. Mikhailov, H. Richard Miller, A.C. Morrill, J. Noble, Paul T. O'Brien, T.D. Oswalt, S.P. Pebley, M. Pfeiffer, V.I. Pronik, B.-C. Qian, J.W. Robertson, A. Robinson, Kenneth S. Rumstay, J. Schmoll, S.G. Sergeev, E.A. Sergeeva, A.I. Shapovalova, D.R. Skillman, Stephanie A. Snedden, S. Soundararajaperumal, G.M. Stirpe, J. Tao, G.W. Turner, R.M. Wagner, S.J. Wagner, J.Y. Wei, H. Wu, W. Zheng, Z.L. Zhou Apr 1998

Steps Toward Determination Of The Size And Structure Of The Broad-Line Region In Active Galactic Nuclei. Xii. Ground-Based Monitoring Of 3c 390.3, M. Dietrich, Bradley M. Peterson, P. Albrecht, M. Altmann, A.J. Barth, P.J. Bennie, R. Bertram, N.G. Bochkarev, H. Bock, J.M. Braun, A. Burenkov, S. Collier, L.-Z. Fang, O.P. Francis, A. V. Filippenko, C.B. Foltz, W. Gassler, C. Martin Gaskell, M. Geffert, K.K. Ghosh, R.W. Hilditch, R.K. Honeycutt, K. Horne, J.P. Huchra, Shai Kaspi, M. Kummel, K.M. Leighly, D.C. Leonard, Yu. F. Malkov, V. Mikhailov, H. Richard Miller, A.C. Morrill, J. Noble, Paul T. O'Brien, T.D. Oswalt, S.P. Pebley, M. Pfeiffer, V.I. Pronik, B.-C. Qian, J.W. Robertson, A. Robinson, Kenneth S. Rumstay, J. Schmoll, S.G. Sergeev, E.A. Sergeeva, A.I. Shapovalova, D.R. Skillman, Stephanie A. Snedden, S. Soundararajaperumal, G.M. Stirpe, J. Tao, G.W. Turner, R.M. Wagner, S.J. Wagner, J.Y. Wei, H. Wu, W. Zheng, Z.L. Zhou

Martin Gaskell Publications

Results of a ground-based optical monitoring campaign on 3C 390.3 in 1994-1995 are presented. The broadband fluxes (B, V , R, and I), the spectrophotometric optical continuum flux Fλ(5177 Å), integrated emission-line fluxes of Hα, Hβ, Hγ, He I λ5876, and He II λ4686 all show a nearly monotonic increase with episodes of milder short-term variations superposed. The amplitude of the continuum variations increases with decreasing wavelength (4400-9000 Å). The optical continuum variations follow the variations in the ultraviolet and X-ray with time delays, measured from the centroids of the crosscorrelation functions, typically around 5 days, but with ...


Steps Toward Determination Of The Size And Structure Of The Broad-Line Region In Active Galactic Nuclei. Xi. Intensive Monitoring Of The Ultraviolet Spectrum Of Ngc 7469, I. Wanders, Bradley M. Peterson, D. Alloin, T.R. Ayres, J. Clavel, D. Michael Crenshaw, K. Horne, Gerard A. Kriss, Julian Henry Krolik, Matthew A. Malkan, Hagai Netzer, Paul T. O'Brien, G.A. Reichert, P.M. Rodriguez-Pascual, W. Wamsteker, T. Alexander, K. S.J. Anderson, E. Benitez, N.G. Bochkarev, A.N. Burenkov, F.-Z. Cheng, S.J. Collier, A. Comastri, M. Dietrich, D. Dultzin-Hacyan, B.R. Espey, A. V. Filippenko, C. Martin Gaskell, I.M. George, M.R. Goad, L.C. Ho, Shai Kaspi, W. Kollatschny, Kirk T. Korista, Ari Laor, G.M. Macalpine, M. Mignoli, S.L. Morris, K. Nandra, S. Penton, Richard William Pogge, R.L. Ptak, J.M. Rodriguez-Espinoza, M. Santos-Lleo, A.I. Shapovalova, J.M. Shull, Stephanie A. Snedden, L.S. Sparke, G.M. Stirpe, W.-H. Sun, T.J. Turner, M.-H. Ulrich, T.-G. Wang, C. Wei, W.F. Welsh, S.-J. Xue, Z.-L. Zhou Nov 1997

Steps Toward Determination Of The Size And Structure Of The Broad-Line Region In Active Galactic Nuclei. Xi. Intensive Monitoring Of The Ultraviolet Spectrum Of Ngc 7469, I. Wanders, Bradley M. Peterson, D. Alloin, T.R. Ayres, J. Clavel, D. Michael Crenshaw, K. Horne, Gerard A. Kriss, Julian Henry Krolik, Matthew A. Malkan, Hagai Netzer, Paul T. O'Brien, G.A. Reichert, P.M. Rodriguez-Pascual, W. Wamsteker, T. Alexander, K. S.J. Anderson, E. Benitez, N.G. Bochkarev, A.N. Burenkov, F.-Z. Cheng, S.J. Collier, A. Comastri, M. Dietrich, D. Dultzin-Hacyan, B.R. Espey, A. V. Filippenko, C. Martin Gaskell, I.M. George, M.R. Goad, L.C. Ho, Shai Kaspi, W. Kollatschny, Kirk T. Korista, Ari Laor, G.M. Macalpine, M. Mignoli, S.L. Morris, K. Nandra, S. Penton, Richard William Pogge, R.L. Ptak, J.M. Rodriguez-Espinoza, M. Santos-Lleo, A.I. Shapovalova, J.M. Shull, Stephanie A. Snedden, L.S. Sparke, G.M. Stirpe, W.-H. Sun, T.J. Turner, M.-H. Ulrich, T.-G. Wang, C. Wei, W.F. Welsh, S.-J. Xue, Z.-L. Zhou

Martin Gaskell Publications

From 1996 June 10 to July 29, the International Ultraviolet Explorer monitored the Seyfert 1 galaxy NGC 7469 continuously in an attempt to measure time delays between the continuum and emission-line fluxes. From the time delays, one can estimate the size of the region dominating the production of the UV emission lines in this source. We find the strong UV emission lines to respond to continuum variations with time delays of about 2.d3-3.d1 for Lyα, 2.d7 for C IV λ1549, 1.d9-2.d4 for N IV λ 1240, 1.d7-1.d ...


Steps Toward Determination Of The Size And Structure Of The Broad-Line Region In Active Galactic Nuclei. Ix. Ultraviolet Observations Of Fairall, P.M. Rodriguez-Pascual, D. Allion, J. Clavel, D. Michael Crenshaw, K. Horne, Gerard A. Kriss, Julian Henry Krolik, Matthew A. Malkan, Hagai Netzer, Paul T. O'Brien, Bradley M. Peterson, G.A. Reichert, W. Wamsteker, T. Alexander, P. Barr, R.D. Blandford, J.N. Bergman, T.E. Carone, S. Clements, T.-J. Courvoisier, M.M. De Robertis, M. Dietrich, H. Dottori, R.A. Edelson, A. V. Filippenko, C. Martin Gaskell, J. P. Huchra, J.B. Hutchings, W. Kollatschny, A.P. Koratkar, Kirk T. Korista, Ari Laor, G.M. Macalpine, P. G. Martin, D. Maoz, B. Mccollum, S.L. Morris, G.C. Perola, Richard William Pogge, R.L. Ptak, M.C. Recondo-Gonzalez, J.M. Rodriguez-Espinoza, E.L. Rokaki, M. Santos-Lleo, K. Sekiguchi, J.M. Schull, M.A.J. Snuders, L.S. Sparke, G.M. Stirpe, R.E. Stoner, W.-H. Sun, S.J. Wagner, I. Wanders, Belinda J. Wilkes, C. Winge, W. Zheng May 1997

Steps Toward Determination Of The Size And Structure Of The Broad-Line Region In Active Galactic Nuclei. Ix. Ultraviolet Observations Of Fairall, P.M. Rodriguez-Pascual, D. Allion, J. Clavel, D. Michael Crenshaw, K. Horne, Gerard A. Kriss, Julian Henry Krolik, Matthew A. Malkan, Hagai Netzer, Paul T. O'Brien, Bradley M. Peterson, G.A. Reichert, W. Wamsteker, T. Alexander, P. Barr, R.D. Blandford, J.N. Bergman, T.E. Carone, S. Clements, T.-J. Courvoisier, M.M. De Robertis, M. Dietrich, H. Dottori, R.A. Edelson, A. V. Filippenko, C. Martin Gaskell, J. P. Huchra, J.B. Hutchings, W. Kollatschny, A.P. Koratkar, Kirk T. Korista, Ari Laor, G.M. Macalpine, P. G. Martin, D. Maoz, B. Mccollum, S.L. Morris, G.C. Perola, Richard William Pogge, R.L. Ptak, M.C. Recondo-Gonzalez, J.M. Rodriguez-Espinoza, E.L. Rokaki, M. Santos-Lleo, K. Sekiguchi, J.M. Schull, M.A.J. Snuders, L.S. Sparke, G.M. Stirpe, R.E. Stoner, W.-H. Sun, S.J. Wagner, I. Wanders, Belinda J. Wilkes, C. Winge, W. Zheng

Martin Gaskell Publications

No abstract provided.


Evidence For Binary Orbital Motion Of A Quasar Broad-Line Region, C. Martin Gaskell Jun 1996

Evidence For Binary Orbital Motion Of A Quasar Broad-Line Region, C. Martin Gaskell

Martin Gaskell Publications

Analysis of spectra of the quasar 3C 390.3 covering a period of over 20 yr shows that the blueshifted peak of H beta has been changing its radial velocity at an almost constant rate during this time. The radial velocity has increased by over 1500 km/s. The lower limit to the period of radial velocity changes is 210 yr. Although very long periods cannot be excluded by the radial velocity curve alone, other considerations suggest that the period is about 300 yr. If the radial velocity changes are due to orbital motion, the radius of the orbit is ...