Now showing items 1-20 of 21

    • Absorption in X-ray spectra of high-redshift quasars 

      Elvis, Martin S.; Fiore, Fabrizio; Wilkes, Belinda Jane; McDowell, Jonathan Christopher; Bechtold, Jill (IOP Publishing, 1994)
      We present evidence that X-ray absorption is common in high-redshift quasars. We have studied six high-redshift (z approximately 3) quasars with the ROSAT Position Sensitive Proportional Counter (PSPC) of which four are ...
    • Atlas of quasar energy distributions 

      Elvis, Martin S.; Wilkes, Belinda Jane; McDowell, Jonathan Christopher; Green, Richard F.; Bechtold, Jill; Willner, Steven P.; Oey, M. S.; Polomski, Elisha; Cutri, Roc (IOP Publishing, 1994)
      We present an atlas of the spectral energy distributions (SEDs) of normal, nonblazar, quasars over the whole available range (radio to 10 keV X-rays) of the electromagnetic spectrum. The primary (UVSX) sample includes 47 ...
    • The Complex Optical to Soft X-Ray Spectrum of Low-Redshift Radio-quiet Quasars. II. Comparison with Free-Free and Accretion Disk Models 

      Fiore, Fabrizio; Elvis, Martin S.; Siemiginowska, Aneta L.; Wilkes, Belinda Jane; McDowell, Jonathan Christopher; Mathur, Smita (IOP Publishing, 1995)
      We compare the optical to soft X-ray spectral energy distributions (SEDs) of a sample of bright low-redshift (0.048 < z < 0.155), radio-quiet quasars, with a range of thermal models which have been proposed to explain the ...
    • The complex optical to soft x-ray spectrum of the low-redshift radio-quiet quasars 

      Fiore, Fabrizio; Elvis, Martin S.; McDowell, Jonathan Christopher; Siemiginowska, Aneta L.; Wilkes, Belinda Jane (IOP Publishing, 1994)
      Eight high signal-to-noise ROSAT Position Sensitive Proportional Counter (PSPC) observations of six low-redshift (o.048 less than z less than 0.155) radio-quiet quasars have been analyzed to study ant soft excess. All the ...
    • EXOSAT X-ray spectra of quasars 

      Comastri, Andrea; Setti, Giancarlo; Zamorani, Giovanni; Elvis, Martin; Wilkes, Belinda Jane; McDowell, Jonathan Christopher; Giommi, Paolo (IOP Publishing, 1992)
      Measurements of the X-ray spectra in the 0.1-10-keV energy range for 17 AGN (mostly PG quasars) using the Exosat Low and Medium Energy arrays are presented. For each object, the best-fit spectral parameters in the medium-energy ...
    • The Far‐Infrared Spectral Energy Distributions of X‐Ray–selected Active Galaxies 

      Kuraszkiewicz, Joanna; Wilkes, Belinda Jane; Eric, undefined; Hooper, J.; McLeod, Kim K.; Wood, Kenneth; Bjorkman, Jon; Delain, Kisha M.; Hughes, David H.; Elvis, Martin S.; Impey, Chris D.; Lonsdale, Carol J.; Malkan, Matt A.; McDowell, Jonathan Christopher; Whitney, Barbara (IOP Publishing, 2003)
      Hard X-ray selection is, arguably, the optimal method for defining a representative sample of active galactic nuclei (AGNs). Hard X-rays are unbiased by the effects of obscuration and reprocessing along the line of sight ...
    • Infrared to x-ray spectral energy distributions of high redshift quasars 

      Bechtold, Jill; Elvis, Martin S.; Fiore, Fabrizio; Kuhn, Olga; Cutri, Roc M.; McDowell, Jonathan Christopher; Rieke, Marcia; Siemiginowska, Aneta L.; Wilkes, Belinda Jane (IOP Publishing, 1994)
      We have observed 14 quasars with z greater than 2.8 with the ROSAT-PSPC, and detected 12 of them, including the z=4.11 quasar 0000-263. We present the first x-ray spectrum of a radio quiet quasar with z greater than 3, ...
    • Investigation of the Relation between the Spectral Energy Distributions and the Emission Lines in Low‐Redshift Quasars 

      Wilkes, Belinda Jane; Kuraszkiewicz, Joanna; Green, Paul J.; Mathur, Smita; McDowell, Jonathan Christopher (IOP Publishing, 1999)
      We investigate the relations between the observed emission-line strengths, widths, and continuum properties of a sample of 41 low-redshift (z<1) quasars for which contemporaneous IR/soft X-ray spectral energy distributions ...
    • Persistence and change in the soft X-ray spectrum of the quasar PG 1211 + 143 

      Elvis, Martin S.; Wilkes, Belinda Jane; Giommi, P.; McDowell, Jonathan Christopher (IOP Publishing, 1991)
      The present study examines two Einstein and three Exosat observations of PG 1211 + 143 over a 6-yr baseline which show that strong steep-spectrum low-energy X-ray emission is a persistent feature of this quasar. Exosat ...
    • PKS 0483-436 - A high-redshift quasar with strong X-ray absorption 

      Wilkes, Belinda Jane; Elvis, Martin S.; Fiore, Fabrizio; McDowell, Jonathan Christopher; Tananbaum, Harvey D.; Lawrence, Andrew (IOP Publishing, 1992)
      The first X-ray spectrum of a high-redshift (z = 2.85) quasar is reported. The Rosat PSPC spectrum of PKS 0438-436, covering 0.3-9 keV in the quasar's rest frame, reveals unexpected absorption of about 1 x 10 exp 22/sq cm, ...
    • Quasar X-ray spectra revisited 

      Shastri, P.; Wilkes, Belinda Jane; Elvis, Martin S.; McDowell, Jonathan Christopher (IOP Publishing, 1993)
      A sample of 45 quasars observed by the IPC on the Einstein satellite is used to re-examine the relationship between the soft (0.2-3.5 keV) X-ray energy index and radio-loudness. We find that, (1) the tendency for radio-loud ...
    • Quasar X-Ray Spectra Revisited: Erratum 

      Shastri, P.; Wilkes, Belinda Jane; Elvis, Martin S.; McDowell, Jonathan Christopher (IOP Publishing, 1994)
      In the paper "Quasar X-Ray Spectra Revisited " by P. Shastri, B. J. Wilkes, M. Elvis, and J. McDowell (ApJ, 410,29 [1993]), there is an error in the flux density levels in Figures 4a and 4b. As a result of an error during ...
    • The ROSAT spectrum of 3C 351 - A warm absorber in an X-ray-'quiet' quasar? 

      Fiore, Fabrizio; Elvis, Martin S.; Mathur, Smita; Wilkes, Belinda Jane; McDowell, Jonathan Christopher (IOP Publishing, 1993)
      3C 351 is one of the most X-ray-quiet radio quasars (alpha(ox) about 1.6). We have observed 3C 351 with the ROSAT position sensitive proportional counter (PSPC) and find a complex X-ray spectrum which is not well reproduced ...
    • The soft X-ray excess in Einstein quasar spectra 

      Masnou, J.; Wilkes, Belinda Jane; Elvis, Martin S.; McDowell, Jonathan Christopher; Arnaud, K. (1991)
      An SNR-limited subsample of 14 quasars from the Wilkes and Elvis (1987) sample is presently investigated for low-energy excess above a high-energy power law in the X-ray spectra obtained by the Einstein Imaging Proportional ...
    • The soft x-ray properties of a complete sample of optically selected quasars. 1: First results 

      Laor, Ari; Fiore, Fabrizio; Elvis, Martin S.; Wilkes, Belinda Jane; McDowell, Jonathan Christopher (IOP Publishing, 1994)
      We present the results of ROSAT position sensitive proportional counter (PSPC) observations of 10 quasars. These objects are part of our ROSAT program to observe a complete sample of optically selected quasars. This sample ...
    • The Soft X‐Ray Properties of a Complete Sample of Optically Selected Quasars. II. Final Results 

      Laor, Ari; Fiore, Fabrizio; Elvis, Martin S.; Wilkes, Belinda Jane; McDowell, Jonathan Christopher (IOP Publishing, 1997)
      We present the final results of a ROSAT PSPC program to study the soft X-ray emission properties of a complete sample of low-z quasars. This sample includes all 23 quasars from the Bright Quasar Survey with z ≤ 0.400 and ...
    • The Spectral Energy Distributions of Red Two Micron All Sky Survey Active Galactic Nuclei 

      Kuraszkiewicz, Joanna; Wilkes, Belinda Jane; Schmidt, Gary; Ghosh, Himel; Smith, Paul S.; Cutri, Roc; Hines, Dean; Huff, Eric M.; McDowell, Jonathan Christopher; Nelson, Brant (IOP Publishing, 2009)
      We present infrared (IR) to X-ray spectral energy distributions (SEDs) for 44 red active galactic nuclei (AGNs) selected from the Two Micron All Sky Survey (2MASS) survey on the basis of their red J − KS color (> 2 mag) ...
    • Testing Models for the Quasar Big Blue Bump via Color-Color Diagrams 

      Siemiginowska, Aneta L.; Kuhn, Olga; Elvis, Martin S.; Fiore, Fabrizio; McDowell, Jonathan Christopher; Wilkes, Belinda Jane (IOP Publishing, 1995)
      We discuss several models of quasar big blue bump emission in color-color and color-luminosity diagrams. We define several broad passbands: IR (0.8-1.6 μm), VIS (4000-8000 Å), UV (1000-2000 Å), UV1 (1400-2000 Å) and UV2 ...
    • The Unusual Quasar PG 1407+265 

      McDowell, Jonathan Christopher; Canizares, Claude; Elvis, Martin S.; Lawrence, Andrew; Markoff, Sera; Mathur, Smita; Wilkes, Belinda Jane (IOP Publishing, 1995)
      PG 1407+265, discovered in the Palomar-Green Survey (Schmidt & Green 1983), was identified as a z ˜ 1 radio-quiet quasar on the basis of a single weak line. Further observations over a wide wavelength range confirm the ...
    • Weak bump quasars 

      McDowell, Jonathan Christopher; Elvis, Martin; Wilkes, Belinda Jane; Willner, Steven P.; Oey, M. S.; Polomski, Elisha; Bechtold, Jill; Green, Richard F. (IOP Publishing, 1989)
      The recent emphasis on big bumps dominating the UV continuum of quasars has obscured the facts that bump properties vary widely and that there are objects in which no such component is evident. As part of a survey of quasar ...