Point source

About: Point source is a research topic. Over the lifetime, 5077 publications have been published within this topic receiving 94091 citations.

The Sunyaev-Zel'dovich effect in WMAP data

Abstract: Using WMAP 5 year data, we look for the average Sunyaev-Zel'dovich effect (SZE) signal from clusters of galaxies by stacking the regions around hundreds of known X-ray clusters. We detect the average SZE at a very high significance level. The average cluster signal is spatially resolved in the W band. This mean signal is compared with the expected signal from the same clusters calculated on the basis of archival ROSAT data. From the comparison we conclude that the observed SZE seems to be less than the expected signal derived from X-ray measurements when a standard beta-model is assumed for the gas distribution. This conclusion is model dependent. Our predictions depend mostly on the assumptions made about the core radius of clusters and the slope of the gas density profile. Models with steeper profiles are able to simultaneously fit both X-ray and WMAP data better than a beta-model. However, the agreement is not perfect and we find that it is still difficult to make the X-ray and SZE results agree. A model assuming point source contamination in SZE clusters renders a better fit to the one-dimensional SZE profiles thus suggesting that contamination from point sources could be contributing to a diminution of the SZE signal. Selecting a model that better fits both X-ray and WMAP data away from the very central region, we estimate the level of contamination and find that on average, the point source contamination is on the level of 16 mJy (at 41 GHz), 26 mJy (at 61 GHz) and 18 mJy (at 94 GHz). These estimated fluxes are marginally consistent with the estimated contamination derived from radio and infrared surveys thus suggesting that the combination of a steeper gas profile and the contribution from point sources allows us to consistently explain the X-ray emission and SZE in galaxy clusters as measured by ROSAT and WMAP.

Overlapping-based optical freeform surface construction for extended lighting source

Abstract: The freeform optical system for an extended source was constructed by partially overlapping a few numbers of point-source freeform surfaces (PFSs) and extracting their contour. Each PFS redistributed the Lambertian emission of a point source into the prescribed light distribution or more frequently into a modified distribution. By adjusting the relative positions of the PFSs and the pattern of the modified light distribution, the optimized freeform surface could be obtained. As an example, an optical system with a height only four times the source radius is designed for achieving a uniform-illuminance distribution on the target. The optimized freeform surface was formed by two PFSs. The virtue-point-sources of the PFSs were located symmetrically on the extended source with a distance of a quarter of the source diameter from each other. Each PFS achieved an increasing-illuminance distribution. The illumination uniformity of this model can be improved by 55.4%, while the optical efficiency within the target area is maintained above 80%.

Chandra Uncovers a Hidden Low-Luminosity Active Galactic Nucleus in the Radio Galaxy Hydra A (3C 218)

Abstract: We report the detection with Chandra of a low-luminosity active galactic nucleus (LLAGN) in the low-ionization nuclear emission-line region (LINER) hosted by Hydra A, a nearby (z = 0.0537) powerful FR I radio galaxy with complex radio and optical morphology. In a 20 ks ACIS-S exposure during the calibration phase of the instrument, a point source is detected at energies 2 keV at the position of the compact radio core, embedded in diffuse thermal X-ray emission (kT ~ 1 keV) at softer energies. The spectrum of the point source is well fitted by a heavily absorbed power law with intrinsic column density N ~ 3 × 1022 cm-2 and photon index Γ ~ 1.7. The intrinsic (absorption-corrected) luminosity is L2-10 keV ~ 1.3 × 1042 ergs s-1. These results provide strong evidence that an obscured AGN is present in the nuclear region of Hydra A. We infer that the optical/UV emission of the AGN is mostly hidden by the heavy intrinsic reddening. In order to balance the photon budget of the nebula, we must either postulate that the ionizing spectrum includes a UV bump or invoke and additional power source (shocks in the cooling flow or interaction with the radio jets). Using an indirect estimate of the black hole mass and the X-ray luminosity, we infer that the accretion rate is low, suggesting that the accretion flow is advection dominated. Finally, our results support current unification schemes for radio-loud sources, in particular the presence of the putative molecular torus in FR I galaxies. These observations underscore the power of the X-rays and of Chandra in the quest for black holes.

Contributions to love-wave transformation theory: Earth-flattening transformation for love waves from a point source in a sphere

Abstract: By means of the Biswas-Knopoff (1970) transformation, programs for the computation of the Love-wave response to a point source in a flat structure can be modified, quite easily, to compute the response in a sphere.