J. Scott Bechtold

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1 Observations here were obtained with the Multiple Mirror Telescope, a joint facility of the University of Arizona and the Smithsonian Institution. – 2 – ABSTRACT We present detections of absorption from the ground state and excited states of C I in the z = 1.9731 damped Lyα system of the QSO 0013−004. The excitation temperature between the J = 0 and J = 1(More)
This paper presents an empirical study comparing the effectiveness of four different versions of an on-line database tutorial, each of which calls upon the student to perform a different kind of inference. The general-to-specific version presents instructions in the form of general rules, from which the students expected to infer how to apply the rule in(More)
We analyze a sample of optical light curves for 100 quasars, 70 of which have black hole mass estimates. Our sample is the largest and broadest used yet for modeling quasar variability. The sources in our sample have z < 2.8, 10 42 λL λ (5100Å) 10 46 , and 10 6 M BH /M ⊙ 10 10. We model the light curves as a continuous time stochastic process, providing a(More)
In this work we use a sample of 318 radio-quiet quasars (RQQ) to investigate the dependence of the ratio of optical/UV flux to X-ray flux, α ox , and the X-ray photon index, Γ X , on black hole mass, UV luminosity relative to Eddington, and X-ray luminosity relative to Eddington. Our sample is drawn from the literature, with X-ray data from ROSAT and(More)
Moderate resolution data for 40 QSOs at z ≈ 2 were combined with spectra of comparable resolution of 59 QSOs with redshifts greater than 1.7 found in the literature to form a large, homogeneous sample of moderate resolution (∼1Å) QSO spectra. These spectra were presented and the statistics of the Lyman α forest were discussed in Paper I. In this analysis,(More)
We report the Chandra discovery of an X-ray cluster at redshift z = 1.063 associated with the Compact Steep Spectrum radio loud quasar 3C 186 (Q0740+380). Diffuse X-ray emission is detected out to ∼ 120 kpc from the quasar and contains 741±40 net counts. The X-ray spectrum of the extended emission shows strong Fe-line emission (EW=412eV) at the quasar(More)
We have discovered an X-ray jet with Chandra imaging of the z=1.187 radio-loud quasar PKS 1127-145. In this paper we present the Chandra X-ray data, follow-up VLA observations, and optical imaging using the HST WFPC2. The X-ray jet contains 273±5 net counts in 27 ksec and extends ∼ 30 ′′ from the quasar core, corresponding to a minimum projected linear size(More)
We report the first significant detection of an X-ray cluster associated with a powerful (L bol ∼ 10 47 erg sec −1) radio-loud quasar at high redshift (z=1.06). Diffuse X-ray emission is detected out to ∼ 120 kpc from the CSS quasar 3C 186. A strong Fe-line emission at the z rest = 1.06 confirms its thermal nature. We find that the CSS radio source is(More)
We present a measurement of the mean intensity of the hydrogen-ionizing background radiation field at low redshift using 906 Lyα absorption lines in 151 quasar spectra from the archives of the Faint Object Spectrograph (FOS) on the Hubble Space Telescope (HST). Using a maximum likelihood technique and the best estimates possible for each QSO's Lyman limit(More)
We have observed three quasars, PKS 1127-145, Q 1331+171 and Q 0054+144, with the ACIS-S aboard the Chandra X-ray Observatory, in order to measure soft X-ray absorption associated with intervening 21-cm and damped Lyα absorbers. For PKS 1127-145, we detect absorption which, if associated with an intervening z abs =0.312 absorber, implies a metallicity of(More)