X-ray transience is the most extreme form of variability observed in AGN or normal in-active galaxies. While factors of 2-3 on timescales of days to years are quite commen among AGN, X-ray transients appear only once and vanish from the X-ray sky years later. The ROSAT All-Sky Survey was the tool to discover these sources. X-ray transience in AGN or galaxies can be caused by dramatic changes in...

Arp 102B is a nearby radio galaxy which displays the presence of doublepeaked Balmer emission lines. Sub-arcsec Keck mid-infrared imaging and Spitzer spectroscopy reveal a spatially compact mid-infrared source which displays tentative evidence for variability. The Fν ∝ ν spectral energy distribution is suggestive of an advection-dominated accretion flow. The absence of dust features over the 5−...

The spectrum and variability of the Seyfert galaxy MCG–6-30-15 can be decomposed into two apparently disconnected components: a highly variable power law and an almost constant component which contains a broad and strong iron line. We explore a possible explanation of the puzzling lack of variability of the iron line, by assuming that the variations of the power law component are due to changes...

We apply the modal coherence theory to evaluate the spatial mode structure of a 2×2 phase-coupled array of vertical cavity surface emitting lasers (VCSELs). The eigenmode structure is extracted for different pump currents by measuring the degree of spatial coherence of all VCSEL pairs in the array. The results reveal the impact of optical disorder and spatial hole burning on the modal discrimin...

We derive the so-called first law of black hole mechanics for variations about stationary black hole solutions to the Einstein–Maxwell equations in the absence of sources. That is, we prove that δM = κδA+ωδJ+V dQ where the black hole parameters M,κ,A, ω, J, V and Q denote mass, surface gravity, horizon area, angular velocity of the horizon, angular momentum, electric potential of the horizon an...

PURPOSE To evaluate the functional outcome and macular index in patients with macular hole who underwent surgery with internal limiting membrane removal. METHODS Fifteen eyes of 15 patients with idiopathic macular hole stages 2, 3 or 4 were enrolled in this study. All patients underwent conventional macular hole surgery with trypan blue staining to remove the internal limiting membrane. The b...

We derive and test a generalization of the steady-state ab initio laser theory (SALT) to treat complex gain media. The generalized theory (C-SALT) is able to treat atomic and molecular gain media with diffusion and multiple lasing transitions, and semiconductor gain media in the free carrier approximation including fully the effect of Pauli blocking. The key assumption of the theory is stationa...

I review current models used to interpret the spectra and variability of microquasars. Among other things, I discuss the structure of the accretion flow and its dependence on mass accretion rate, the intrinsic connection between hot comptonizing corona and compact radio jet in the hard state, as well as possible models for the spectral hysteresis observed during outbursts of transient sources. ...

We present the long term evolution of the timing properties of the black hole candidate Cygnus X-1 in the 0.002– 128 Hz frequency range as monitored from 1998 to 2001 with the Rossi X-ray Timing Explorer (RXTE). For most of this period the source was in its hard state. The power spectral density (PSD) is well modeled as the sum of four Lorentzians, which describe distinct broad noise components...

We summarize the current state of polarization observations of Sagittarius A*, the compact radio source and supermassive black hole candidate in the Galactic Center. These observations are providing new tools for understanding accretion disks, jets and their environments. Linear polarization observations have shown that Sgr A* is unpolarized at frequencies as high as 86 GHz. However, recent sin...