Thomas L. Aldcroft

A Chandra Survey of Broad Absorption Line Quasars

We have carried out a survey with the Chandra X-Ray Observatory of a sample of 10 bright broad absorption line (BAL) quasars (QSOs). Eight of 10 sources are detected. The six brightest sources have only high-ionization BALs (hiBALs), while the four faintest all show low-ionization BALs (loBALs). We perform a combined spectral fit for hiBAL QSOs (384 counts total; 0.5-6 keV) to determine the mean spectral parameters of this sample. We derive an underlying best-fit power-law slope Γ = 1.8 ± 0.35, which is consistent with the mean slope for radio-quiet QSOs from ASCA, but BAL QSOs require a (rest-frame) absorbing column of 6.5 × 1022 cm-2, with a partial covering fraction of ~80%. The optical-to-X-ray spectral slope (αox from 2500 A to 2 keV) varies from 1.7 to 2.4 across the full sample, consistent with previous results that BAL QSOs appear to be weak soft X-ray emitters. Removing the absorption component from our best-fit spectral model yields a range of αox from 1.55 to 2.28. All six hiBAL QSOs have deabsorbed X-ray emission consistent with non-BAL QSOs of similar luminosity. The spectral energy distributions of the hiBAL QSOs—both the underlying power-law slope and αox—provide the first conclusive evidence that BAL QSOs have appeared to be X-ray weak because of intrinsic absorption and that their underlying emission is consistent with non-BAL QSOs. By contrast, the removal of the best-fit absorption column detected in the hiBAL QSOs still leaves the four loBAL QSOs with values of αox > 2 that are unusually X-ray faint for their optical luminosities, which is consistent with other evidence that loBALs have higher column density, dustier absorbers. Important questions of whether BAL QSOs represent a special line of sight toward a QSO nucleus or rather an early evolutionary or high-accretion phase in a QSO lifetime remain to be resolved, and the unique properties of loBAL QSOs will be an integral part of that investigation.

Chandra Discovery of a 300 Kiloparsec X-Ray Jet in the Gigahertz-peaked Spectrum Quasar PKS 1127–145

We have discovered an X-ray jet with Chandra imaging of the z=1.187 radioloud 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 of ∼ 330h 50 kpc. The evaluation of the X-ray emission processes is complicated by the observed offsets between X-ray and radio brightness peaks. We discuss the problems posed by these observations to jet models. In addition, PKS 1127-145 is a Giga-Hertz Peaked Spectrum radio source, a member of the class of radio sources suspected to be young or “frustrated” versions of FRI radio galaxies. However the discovery of an X-ray and radio jet extending well outside the host galaxy of PKS 1127145 suggests that activity in this and other GPS sources may be long-lived and complex. Subject headings: Quasars: individual (PKS 1127-145) – galaxies: jets – X-Rays:

Chandra Survey of Radio-quiet, High-Redshift Quasars

We observed 17 optically selected, radio-quiet, high-redshift quasars with the Chandra ACIS and detected 16 of them. The quasars have redshifts between 3.70 and 6.28 and include the highest-redshift quasars known. When compared with low-redshift quasars observed with ROSAT, these high-redshift quasars are significantly more X-ray-quiet. We also find that the X-ray spectral index of the high-redshift objects is flatter than the average at lower redshift. These trends confirm the predictions of models in which the accretion flow is described by a cold, optically thick accretion disk surrounded by a hot, optically thin corona, provided the viscosity parameter α ≥ 0.02. The high-redshift quasars have supermassive black holes, with masses of ~1010 M☉, and are accreting material at ~0.1 times the Eddington limit. We detect 10 X-ray photons from the z = 6.28 quasar SDSS 1030+0524, which might have a Gunn-Peterson trough and be near the redshift of reionization of the intergalactic medium. The X-ray data place an upper limit on the optical depth of the intergalactic medium, τ(IGM) 20.

Mg II absorption in a sample of 56 steep-spectrum quasars

We present an analysis of the statistical properties of Mg II absorbers found in the spectra of 56 intrinsically faint, steep-spectrum radio quasars. We observe for the first time a significant excess of associated Mg II absorbers over the number expected from cosmologically distributed absorbers. This result is in contrast to previous Mg II surveys in which the QSOs were optically selected. This distinction is similar to the result for associated C IV absorbers, in which intrinsically faint, steep-spectrum quasars show excess associated absorption and intrinsically bright QSOs (both radio-loud and radio-quiet) do not show an excess. From our spectra a statistically complete list of absorption lines is derived, and we find 29 Mg II absorbers, 18 of which have not been previously reported. We also determine several characteristics of the quasar emission lines in our spectra. The Mg II absorber distribution as a function of redshift and equivalent width is calculated both for our sample alone and from our sample combined with spectra from other surveys. For the redshift distribution n(z) = n(1 + z)(exp gamma), we obtain, using the combined sample, the values gamma = 1.11 +/- 0.46 for W(min) = 0.6 A and gamma = 2.47 +/- 0.68 for W(min) = 1.0 A. We find that the distribution fo strong absorbers is inconsistent with no evolution at a confindence level between 2.2 and 2.9 sigma, depending on the deceleration parameter q(sub 0). The deviation from no evolution is similar to what had been previously reported.

Emission Line Properties of the Large Bright Quasar Survey

We present measurements of the optical/UV emission lines for a large homogeneous sample of 993 quasars from the Large Bright Quasar Survey. Our largely automated technique accounts for continuum breaks and galactic reddening, and we perform multicomponent fits to emission line profiles, including the effects of blended iron emission, and of absorption lines both galactic and intrinsic. Here we describe the fitting algorithm and present the results of line fits to the LBQS sample, including upper limits to line equivalent widths when warranted. The distribution of measured line parameters, principally Wλ and FWHM, are detailed for a variety of lines, including upper limits. We thus initiate a large-scale investigation of correlations between the high-energy continuum and emission lines in quasars, to be extended to complementary samples using similar techniques. High-quality, reproducible measurements of emission lines for uniformly selected samples will advance our understanding of active galaxies, especially in a new era of large surveys selected by a variety of complementary methods.

An Overview of the Performance of the Chandra X-ray Observatory

The Chandra X-ray Observatory is the X-ray component of NASAs Great Observatory Program which includes the recently launched Spitzer Infrared Telescope, the Hubble Space Telescope (HST) for observations in the visible, and the Compton Gamma-Ray Observatory (CGRO) which, after providing years of useful data has reentered the atmosphere. All these facilities provide, or provided, scientific data to the international astronomical community in response to peer-reviewed proposals for their use. The Chandra X-ray Observatory was the result of the efforts of many academic, commercial, and government organizations primarily in the United States but also in Europe. NASAs Marshall Space Flight Center (MSFC) manages the project and provides project science; Northrop Grumman Space Technology (NGST – formerly TRW) served as prime contractor responsible for providing the spacecraft, the telescope, and assembling and testing the observatory; and the Smithsonian Astrophysical Observatory (SAO) provides technical support and is responsible for ground operations including the Chandra X-ray Center (CXC). Telescope and instrument teams at SAO, the Massachusetts Institute of Technology (MIT), the Pennsylvania State University (PSU), the Space Research Institute of the Netherlands (SRON), the Max-Planck Institüt für extraterrestrische Physik (MPE), and the University of Kiel also provide technical support to the Chandra Project. We present here a detailed description of the hardware, its on-orbit performance, and a brief overview of some of the remarkable discoveries that illustrate that performance.

CHANDRA HIGH-RESOLUTION OBSERVATIONS OF CID-42, A CANDIDATE RECOILING SUPERMASSIVE BLACK HOLE

We present Chandra High Resolution Camera observations of CID-42, a candidate recoiling supermassive black hole (SMBH) at z = 0.359 in the COSMOS survey. CID-42 shows two optical compact sources resolved in the HST/ACS image embedded in the same galaxy structure and a velocity offset of ~1300 km s–1 between the Hβ broad and narrow emission line, as presented by Civano et al. Two scenarios have been proposed to explain the properties of CID-42: a gravitational wave (GW) recoiling SMBH and a double Type 1/Type 2 active galactic nucleus (AGN) system, where one of the two is recoiling because of slingshot effect. In both scenarios, one of the optical nuclei hosts an unobscured AGN, while the other one, either an obscured AGN or a star-forming compact region. The X-ray Chandra data allow us to unambiguously resolve the X-ray emission and unveil the nature of the two optical sources in CID-42. We find that only one of the optical nuclei is responsible for the whole X-ray unobscured emission observed and a 3σ upper limit on the flux of the second optical nucleus is measured. The upper limit on the X-ray luminosity plus the analysis of the multiwavelength spectral energy distribution indicate the presence of a star-forming region in the second source rather than an obscured SMBH, thus favoring the GW recoil scenario. However, the presence of a very obscured SMBH cannot be fully ruled out. A new X-ray feature, in a SW direction with respect to the main source, is discovered and discussed.

Chandra detection of X-ray absorption associated with a damped Lyα system

We have observed three quasars, PKS 1127-145, Q1331+171, and Q0054+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 Ly? absorbers. For PKS 1127-145, we detect absorption that, if associated with an intervening zabs = 0.312 absorber, implies a metallicity of 23% solar. If the absorption is not at zabs = 0.312, then the metallicity is still constrained to be less than 23% solar. The advantage of the X-ray measurement is that the derived metallicity is insensitive to ionization, inclusion of an atom in a molecule, or depletion onto grains. The X-ray absorption is mostly due to oxygen and is consistent with the oxygen abundance of 30% solar derived from optical nebular emission lines in a foreground galaxy at the redshift of the absorber. For Q1331+171 and Q0054+144, only upper limits were obtained, although the exposure times were intentionally short, since for these two objects we were interested primarily in measuring flux levels to plan for future observations. The imaging results are presented in a companion paper.

Initial performance of the aspect system on the Chandra Observatory: postfacto aspect reconstruction

The aspect system of the Chandra Observatory plays a key role in realizing the full potential of Chandras X-ray optics and detectors. To achieve the highest spatial and spectral resolution (for grating observations), an accurate post-facto time history of the spacecraft attitude and internal alignment is needed. The CXC has developed a suite of tools which process sensor data from the aspect camera assembly and gyroscopes, and produce the spacecraft aspect solution. In this poster, the design of the aspect pipeline software is briefly described, followed by details of aspect system performance during the first eight months of flight. The two key metrics of aspect performance are: image reconstruction accuracy, which measures the X-ray image blurring introduced by aspect; and celestial location, which is the accuracy of detected source positions in absolute sky coordinates.

X-ray cluster associated with the z = 1.063 CSS quasar 3C 186: The jet is not frustrated

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 redshift and confirms the thermal nature of this diffuse component. We measure a cluster temperature of 5.2 +1.2 −0.9 keV and an X-ray luminosity L(0.5−2keV) � 6 × 10 44 erg sec −1 , which are in agreement with the luminosity-temperature relation for high-redshift clusters. This is the first detection of a bright X-ray cluster around a luminous (Lbol �10 47 erg sec −1 ) CSS quasar at high redshift and only the fifth z > 1 X-ray cluster detected. We find that the CSS radio source is highly overpressured with respect to the thermal cluster medium by about 3 orders of magnitude. This provides direct observational evidence that the radio source is not thermally confined as posited in the “frustrated” scenario for CSS sources. Instead, it appears that the radio source may be young and we are observing it at an early stage of its evolution. In that case the radio source could supply the energy into the cluster and potentially prevent its cooling. Subject headings: quasars: individual (3C 186) - X-rays: galaxies: clusters