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During an intensive Hubble Space Telescope (HST) Cosmic Origins Spectrograph (COS) UV monitoring campaign of the Seyfert 1 galaxy NGC 5548 performed from 2014 February to July, the normally highly correlated far UV continuum and broad emission line variations decorrelated for ∼60-70 days, starting ∼75 days after the first HST/COS observation. Following this anomalous state, the flux and variability of the broad emission lines returned to a more normal state. This transient behavior, characterized by significant deficits in flux and equivalent width of the strong broad UV emission lines, is the first of its kind to be unambiguously identified in an active galactic nucleus reverberation mapping campaign. The largest corresponding emission line flux deficits occurred for the high ionization, collisionally excited lines C iv and Si iv(+O iv]), and also He ii(+O iii]), while the anomaly in Lywas substantially smaller. This pattern of behavior indicates a depletion in the flux of photons with relative to those near 13.6 eV. We suggest two plausible mechanisms for the observed behavior: (i) temporary obscuration of the ionizing continuum incident upon broad line region (BLR) clouds by a moving veil of material lying between the inner accretion disk and inner (BLR), perhaps resulting from an episodic ejection of material from the disk, or (ii) a temporary change in the intrinsic ionizing continuum spectral energy distribution resulting in a deficit of ionizing photons with energies >54 eV, possibly due to a transient restructuring of the Comptonizing atmosphere above the disk. Current evidence appears to favor the latter explanation.

In Spring 2011, the Lick AGN Monitoring Project observed a sample of 15 bright, nearby Seyfert 1 galaxies in the V band as part of a reverberation mapping campaign. The observations were taken at six ground-based telescopes, including the West Mountain Observatory 0.91 m telescope, the 0.76 m Katzman Automatic Imaging Telescope, 0.6 m Super-LOTIS at Kitt Peak, the Palomar 60 inch telescope, and the 2 m Faulkes telescopes North and South. The V-band light curves measure the continuum variability of our sample of Seyferts on an almost daily cadence for 2–3 months. We use image-subtraction software to isolate the variability of the Seyfert nucleus from the constant V-band flux of the host galaxy for the most promising targets, and we adopt standard aperture photometry techniques for the targets with smaller levels of variability. These V-band light curves will be used, with measurements of the broad emission line flux, to measure supermassive black hole masses and to constrain the geometry and dynamics of the broad-line region through dynamical modeling techniques. [ABSTRACT FROM AUTHOR]

Observations and numerical simulations of galaxy clusters strongly indicate that the hot intracluster X-ray-emitting gas is not spherically symmetric. In many earlier studies, spherical symmetry has been assumed partly because of limited data quality; however, new deep observations and instrumental designs will make it possible to go beyond that assumption. Measuring the temperature and density profiles are of interest when observing the X-ray gas; however, the spatial shape of the gas itself also carries very useful information. For example, it is believed that the X-ray gas shape in the inner parts of galaxy clusters is greatly affected by feedback mechanisms, cooling, and rotation, and measuring this shape can therefore indirectly provide information on these mechanisms. In this paper, we present a novel method to measure the three-dimensional shape of the intracluster X-ray-emitting gas. We can measure the shape from X-ray observations only, i.e., the method does not require combination with independent measurements of, e.g., the cluster mass or density profile. This is possible when one uses the full spectral information contained in the observed spectra. We demonstrate the method by measuring radially dependent shapes along the line of sight for CHANDRA mock data. We find that at least 106 photons are required to get a 5σ detection of shape for an X-ray gas having realistic features such as a cool core and a double power law for the density profile. We illustrate how Bayes’ theorem is used to find the best-fitting model of the X-ray gas, an analysis that is very important in a real observational scenario where the true spatial shape is unknown. Not including a shape in the fit may propagate to a mass bias if the X-ray is used to estimate the total cluster mass. We discuss this mass bias for a class of spatial shapes. [ABSTRACT FROM AUTHOR]