Reverberation Mapping of High-Luminosity Quasars: First Results

Reverberation mapping of nearby active galactic nuclei has led to estimates of broad-line-region (BLR) sizes and central-object masses for some 37 objects to date. However, successful reverberation mapping has yet to be performed for quasars of either high luminosity (above L_opt~10^{46} erg/s) or high redshift (z>0.3). Over the past six years, we have carried out, at the Hobby-Eberly Telescope, rest-frame-ultraviolet spectrophotometric monitoring of a sample of six quasars at redshifts z=2.2--3.2, with luminosities of L_opt~10^{46.4}--10^{47.6} erg/s, an order of magnitude greater than those of previously mapped quasars. The six quasars, together with an additional five having similar redshift and luminosity properties, were monitored photometrically at the Wise Observatory during the past decade. All 11 quasars monitored show significant continuum variations of order 10%--70%. This is about a factor of two smaller variability than for lower luminosity quasars monitored over the same rest-frame period. In the six objects which have been spectrophotometrically monitored, significant variability is detected in the CIV1550 broad emission line. In several cases the variations track the continuum variations in the same quasar, with amplitudes comparable to, or even greater than, those of the corresponding continua. In contrast, no significant Ly\alpha variability is detected in any of the four objects in which it was observed. Thus, UV lines may have different variability trends in high-luminosity and low-luminosity AGNs. For one quasar, S5~0836+71 at z=2.172, we measure a tentative delay of 595 days between CIV and UV-continuum variations, corresponding to a rest-frame delay of 188 days and a central black-hole mass of 2.6\times10^9 M_\odot.Comment: 11 pages, 6 figures, emulateapj, accepted for publication in The Astrophysical Journa

Quasar Parallax: a Method for Determining Direct Geometrical Distances to Quasars

We describe a novel method to determine direct geometrical distances to quasars that can measure the cosmological constant, Lambda, with minimal assumptions. This method is equivalent to geometric parallax, with the `standard length' being the size of the quasar broad emission line region (BELR) as determined from the light travel time measurements of reverberation mapping. The effect of non-zero Lambda on angular diameter is large, 40% at z=2, so mapping angular diameter distances vs. redshift will give Lambda with (relative) ease. In principle these measurements could be made in the UV, optical, near infrared or even X-ray bands. Interferometers with a resolution of 0.01mas are needed to measure the size of the BELR in z=2 quasars, which appear plausible given reasonable short term extrapolations of current technology.Comment: 13 pages, with 3 figures. ApJ Letters, in press (Dec 20, 2002

A Validation of Mathematical Models for Turbojet Test Cells

Prepared for: Naval Air Propulsion Center Trenton, NJ 09628Previously developed one-dimensional and two-dimensional computer models fox predicting turbojet test cell performance were compared with data obtained from a subscale test cell for the purpose of model validation. Comparisons were made for a variety of configurations and flow rates. A modified one-dimensional mode was found to reasonably predict the variation of augmentation ratio with engine flow; rate, although predicted magnitudes were consistently too small. The model incorporated excess we drag losses and an inaccurate jet spreading para-meter for large engine-augmentor spacings. The two-dimensional model accurately predicted experimental. velocity profiles, but over-predicted pressure variations, except for low engine exit Mach numbers.Naval Air Propulsion Center, Trenton, NJApproved for public release; distribution is unlimited

Reversible Eu²⁺ ↔ Eu³⁺ transitions at Eu‐Si interfaces

Valence switching at Eu‐Si interfaces is demonstrated by resonant photoemission during repeated oxidation‐reduction cycles performed by room‐temperature O2 exposure and mild heating. The Eu2+ ↔ Eu3+ transitions are accompanied by Fermi level switching associated with changes in the stoichiometry of the surface heterostructure. The ability to cycle between two well‐defined magnetic states at a surface may be attractive in technological applications

Ionized Ultraviolet and Soft-X-ray Absorptions in the Low Redshift Active Galactic Nucleus PG1126-041

We present here the analysis of ultraviolet spectra from IUE and an X-ray spectrum from ROSAT PSPC observations of the X-ray weak, far-infrared loud AGN, PG 1126-041 (Mrk 1298). The first UV spectra taken in June 1992, simultaneously with ROSAT, show strong absorption lines of NV, CIV and SiIV, extending over a velocity range from -1000 to -5000 km/s with respect to the corresponding line centre. Our analysis shows that the Broad Emission Line Region (BELR) is, at least partially, covered by the material causing these absorption lines. In the IUE spectrum taken in Jan. 1995, the continuum was a factor of two brighter and the UV absorption lines are found to be considerably weaker than in 1992, but only little variation in the emission line fluxes is found. With UV spectral indices of A_{uv} \simeq 1.82 and 1.46 for the 1992 and 1995 data, the far UV spectrum is steep. Based on the emission line ratios and the broad band spectral energy distribution, we argue that the steepness of the UV spectrum is unlikely to be due to reddening. The soft X-ray emission in the ROSAT band is weak. A simple power-law model yields a very poor fit with a UV-to-X-ray spectral index A_{uvx}=2.32. Highly ionized (warm) absorption is suggested by the ROSAT data. After correcting for a warm absorber, the optical to X-ray spectral slope is close to the average of A{uvx}\simeq 1.67 for radio quiet quasars.Comment: 8 pages, 9 postscript figures. Mon. Not. Roy. Astr. Soc., accepte

The Hard X-ray Spectral Slope as an Accretion-Rate Indicator in Radio-Quiet Active Galactic Nuclei

We present new XMM-Newton observations of two luminous and high accretion-rate radio-quiet active galactic nuclei (AGNs) at z~2. Together with archival X-ray and rest-frame optical spectra of three sources with similar properties as well as 25 moderate-luminosity radio-quiet AGNs at z<0.5, we investigate, for the first time, the dependence of the hard (>~2 keV) X-ray power-law photon index on the broad H_beta emission-line width and on the accretion rate across ~3 orders of magnitude in AGN luminosity. Provided the accretion rates of the five luminous sources can be estimated by extrapolating the well-known broad-line region size-luminosity relation to high luminosities, we find that the photon indices of these sources, while consistent with those expected from their accretion rates, are significantly higher than expected from the widths of their H_beta lines. We argue that, within the limits of our sample, the hard-X-ray photon index depends primarily on the accretion rate.Comment: 4 pages (emulateapj), 2 figures. Accepted for publication in ApJ Letter

The Radius-Luminosity Relationship For Active Galactic Nuclei: The Effect of Host-Galaxy Starlight On Luminosity Measurements. II. The Full Sample of Reverberation-Mapped AGNs

We present high-resolution Hubble Space Telescope images of all 35 active galactic nuclei (AGNs) with optical reverberation-mapping results, which we have modeled to create a nucleus-free image of each AGN host galaxy. From the nucleus-free images, we determine the host-galaxy contribution to ground-based spectroscopic luminosity measurements at 5100 Å. After correcting the luminosities of the AGNs for the contribution from starlight, we re-examine the Hβ R_BLR-L relationship. Our best fit for the relationship gives a power-law slope of 0.52 with a range of 0.45-0.59 allowed by the uncertainties. This is consistent with our previous findings, and thus still consistent with the naive assumption that all AGNs are simply luminosity-scaled versions of each other. We discuss various consistency checks relating to the galaxy modeling and starlight contributions, as well as possible systematic errors in the current set of reverberation measurements from which we determine the form of the R_BLR-L relationship

Reverberation Mapping and the Physics of Active Galactic Nuclei

Reverberation-mapping campaigns have revolutionized our understanding of AGN. They have allowed the direct determination of the broad-line region size, enabled mapping of the gas distribution around the central black hole, and are starting to resolve the continuum source structure. This review describes the recent and successful campaigns of the International AGN Watch consortium, outlines the theoretical background of reverberation mapping and the calculation of transfer functions, and addresses the fundamental difficulties of such experiments. It shows that such large-scale experiments have resulted in a ``new BLR'' which is considerably different from the one we knew just ten years ago. We discuss in some detail the more important new results, including the luminosity-size-mass relationship for AGN, and suggest ways to proceed in the near future.Comment: Review article to appear in Astronomical Time Series, Proceedings of the Wise Observatory 25th Ann. Symposium. 24 pages including 7 figure