Point source

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

Apparent initial phase of a source of Rayleigh waves

Abstract: The apparent initial phase of a point source of Rayleigh waves is shown to depend on the inclination of the source to the vertical. This effect is frequency dependent; the frequency dependence vanishes for a vertical or horizontal source. Corrections must therefore be applied to the phase velocities determined by the single-station method and, less significantly, to group velocities; these corrections depend on a knowledge of the angle of inclination of the source.

The optical and ultraviolet spectral energy distributions of short-period black hole X-ray transients in outburst

Abstract: We compile optical and UV spectra of a sample of "typical" short-period black hole X-ray transients in outburst. We also survey determinations of interstellar extinction and distance to deredden spectra and compare absolute fluxes. Hence, we perform a comparative study of the broadband spectral energy distributions (SEDs). We find that, given such a homogeneous sample of typical sources, the optical SEDs form a relatively uniform set, all exhibiting quasi-power-law spectra with Fν ∝ να, where 0.5 α 1.5 (steeper than the canonical ν1/3 disk spectrum). All become flatter in the UV, although there is more diversity here. The SEDs studied can be broadly divided into two optical-UV spectral states. The UV-hard spectra, e.g., A0620-00 and GS 1124-684, continue to rise in the far-UV. The UV-soft spectra, e.g., GRO J0422+32, drop off. XTE J1859+226 evolved from UV-soft to UV-hard as it decayed, indicating that this effect is a real difference, not a dereddening artifact. All the spectra can be fitted by a generalized blackbody disk model with two forms of heating, resulting in the two states. The UV-soft state is consistent with a disk illuminated by a central point source, with irradiative heating dominating over viscous. The UV-hard state is well described by a viscously heated disk, although this requires very high mass flow rates in the case of GS 1124-684. Alternatively, a UV-hard spectrum can be produced if the disk is illuminated by a vertically extended X-ray source such as a central scattering corona or jet. Since scattering is assumed by some numerical simulations, it is worth emphasizing that when illumination comes from (nonlocal) scattering high above the disk, we generically expect a steeper radial dependence of X-ray heating (F ∝ R-3) than is usually assumed; it is this steep dependence that leads to the UV-hard spectrum.

The XMM-Newton deep survey in the Chandra Deep Field South. III. Point source catalogue and number counts in the hard X-rays ?

Abstract: Nuclear obscuration plays a key role in the initial phases of AGN growth, yet not many highly obscured AGN are currently known beyond the local Universe, and their search is an active topic of research. The XMM-Newton survey in the Chandra Deep Field South (XMM-CDFS) aims at detecting and studying the spectral properties of a significant number of obscured and Compton-thick (NH & 10 24 cm 2 ) AGN. The large e ective area of XMM-Newton in the 2‐10 and 5‐10 keV bands, coupled with a 3.45 Ms nominal exposure time (2.82 and 2.45 Ms after lightcurve cleaning for MOS and PN respectively), allows us to build clean samples in both bands, and makes the XMM-CDFS the deepest XMM-Newton survey currently published in the 5‐10 keV band. The large multiwavelength and spectroscopic coverage of the CDFS area allows for an immediate and abundant scientific return. In this paper, we present the data reduction of the XMM-CDFS observations, the method for source detection in the 2‐10 and 5‐10 keV bands, and the resulting catalogues. A number of 339 and 137 sources are listed in the above bands with flux limits of 6:6 10 16 and 9:5 10 16 erg s 1 cm 2 , respectively. The flux limits at 50% of the maximum sky coverage are 1:8 10 15 and 4:0 10 15 erg s 1 cm 2 , respectively. The catalogues have been cross-correlated with the Chandra ones: 315 and 130 identifications have been found with a likelihoodratio method, respectively. A number of 15 new sources, previously undetected by Chandra, is found; 5 of them lie in the 4 Ms area. Redshifts, either spectroscopic or photometric, are available for 92% of the sources. The number counts in both bands are presented and compared to other works. The survey coverage has been calculated with the help of two extensive sets of simulations, one set per band. The simulations have been produced with a newly-developed simulator, written with the aim of the most careful reproduction of the background spatial properties. For this reason, we present a detailed decomposition of the XMM-Newton background into its components: cosmic, particle, and residual soft protons. The three components have di erent spatial distributions. The importance of these three components depends on the band and on the camera; the particle background is the most important one (80‐90% of the background counts), followed by the soft protons (4‐20%).

Parametrizing Epoch of Reionization foregrounds: a deep survey of low-frequency point-source spectra with the Murchison Widefield Array

Abstract: Experiments that pursue detection of signals from the Epoch of Reionization (EoR) are relying on spectral smoothness of source spectra at low frequencies. This article empirically explores the effect of foreground spectra on EoR experiments by measuring high-resolution full-polarization spectra for the 586 brightest unresolved sources in one of the Murchison Widefield Array (MWA) EoR fields using 45 h of observation. A novel peeling scheme is used to subtract 2500 sources from the visibilities with ionospheric and beam corrections, resulting in the deepest, confusion-limited MWA image so far. The resulting spectra are found to be affected by instrumental effects, which limit the constraints that can be set on source-intrinsic spectral structure. The sensitivity and power-spectrum of the spectra are analysed, and it is found that the spectra of residuals are dominated by point spread function sidelobes from nearby undeconvolved sources. We release a catalogue describing the spectral parameters for each measured source.