Search

Active galactic nuclei (AGNs) that show strong rest-frame optical/UV variability in their blue continuum and broad line emission are classified as changing-look AGN, or at higher luminosities, changing-look quasars (CLQs). These surprisingly large and sometimes rapid transitions challenge accepted models of quasar physics and duty cycles, offer several new avenues for study of quasar host galaxies, and open a wider interpretation of the cause of differences between broad and narrow-line AGN. To better characterize extreme quasar variability, we present follow-up spectroscopy as part of a comprehensive search for CLQs across the full Sloan Digital Sky Survey (SDSS) footprint using spectroscopically confirmed quasars from the SDSS DR7 catalog. Our primary selection requires large-amplitude ( mag, mag) variability over any of the available time baselines probed by the SDSS and Pan-STARRS 1 surveys. We employ photometry from the Catalina Sky Survey to verify variability behavior in CLQ candidates where available, and confirm CLQs using optical spectroscopy from the William Herschel, MMT, Magellan, and Palomar telescopes. For our adopted signal-to-noise ratio threshold on variability of broad Hβ emission, we find 17 new CLQs, yielding a confirmation rate of ≳20%. These candidates are at lower Eddington ratio relative to the overall quasar population, which supports a disk-wind model for the broad line region. Based on our sample, the CLQ fraction increases from 10% to roughly half as the continuum flux ratio between repeat spectra at 3420 Å increases from 1.5 to 6. We release a catalog of more than 200 highly variable candidates to facilitate future CLQ searches. [ABSTRACT FROM AUTHOR]

We perform a systematic study of outflow in the narrow-line region (NLR) of active galactic nuclei (AGNs) at z ∼ 0.4–0.8 based upon a large sample of ∼900 quasars at z ∼ 0.4–0.8. The sample is extracted from the Sloan Digital Sky Survey by mainly requiring that (1) the g-band magnitude is brighter than 19 mag and (2) the [O iii]λ5007 emission line has a signal-to-noise ratio larger than 30. Profiles of multiple emission lines are modeled by a sum of several Gaussian functions. The spectral analysis allows us to identify (1) a prevalence of both [O iii]λ5007 line blue asymmetry and bulk velocity blueshift of both [Ne iii]λ3869 and [Ne iii]λ3426 lines, when the [O ii]λ3727 line is used as a reference. The velocity offset of the [O iii]λ5007 line is, however, distributed around a value of zero, except for a few outliers. (2) Not only the significant [O iii]λ5007 line asymmetry, but also the large bulk velocity offsets of [Ne iii]λ3869 and [Ne v]λ3426 emission lines tend to occur in the objects with high L/LEdd, which is considerably consistent with the conclusions based on local AGNs. With three MBH estimation methods, the significance level of the trend is found to be better than 2.9σ, 3.2σ, and 1.8σ for [O iii], [Ne iii], and [Ne v], respectively. After excluding the role of radio jets, the revealed dependence of NLR gas outflow on L/LEdd allows us to argue that the pressure caused by the wind/radiation launched/emitted from a central supermassive black hole is the most likely origin of the outflow in these distant quasars, which implies that the outflow in luminous AGNs up to z ∼ 1 have the same origin. [ABSTRACT FROM AUTHOR]

We present the results of recent Chandra, XMM-Newton, and Hubble Space Telescope observations of the radio-loud (RL), broad absorption line (BAL) quasar PG 1004+130. We compare our new observations to archival X-ray and UV data, creating the most comprehensive, high signal-to-noise, multi-epoch, spectral monitoring campaign of a RL BAL quasar to date. We probe for variability of the X-ray absorption, the UV BAL, and the X-ray jet, on month–year timescales. The X-ray absorber has a low column density of when it is assumed to be fully covering the X-ray emitting region, and its properties do not vary significantly between the four observations. This suggests that the observed absorption is not related to the typical “shielding gas” commonly invoked in BAL quasar models, but is likely due to material further from the central black hole. In contrast, the C iv BAL shows strong variability. The equivalent width (EW) in 2014 is , showing a fractional increase of from the 2003 observation, 3183 days earlier in the rest-frame. This places PG 1004+130 among the most highly variable BAL quasars. By combining Chandra observations we create an exposure that is 2.5 times deeper than studied previously, with which to investigate the nature of the X-ray jet and extended diffuse X-ray emission. An X-ray knot, likely with a synchrotron origin, is detected in the radio jet (30 kpc) from the central X-ray source with a spatial extent of (15 kpc). No similar X-ray counterpart to the counterjet is detected. Asymmetric, non-thermal diffuse X-ray emission, likely due to inverse Compton scattering of Cosmic Microwave Background photons, is also detected. [ABSTRACT FROM AUTHOR]