Point source

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

X-ray Observations of the New Pulsar--Supernova Remnant System PSR J1119-6127 and SNR G292.2-0.5

Abstract: PSR J1119-6127 is a recently discovered 1700-year-old radio pulsar that has a very high inferred surface dipolar magnetic field. We present a detailed analysis of a pointed ASCA observation and archival ROSAT data of J1119-6127 and its surroundings. Both data sets reveal extended emission coincident with the newly-discovered radio supernova remnant G292.2-0.5, reported in a companion paper by Crawford et al. (astro-ph/0012287).. A hard point source, offset ~1.5' from the position of the radio pulsar, is seen with the ASCA GIS. No pulsations are detected at the radio period with a pulsed fraction upper limit of 61% (95% confidence). The limited statistics prevent a detailed spectral analysis, although a power-law model with photon index (Gamma=~1-2) describes the data well. Both the spectral model and derived X-ray luminosity are consistent with those measured for other young radio pulsars, although the spatial offset renders an identification of the source as the X-ray counterpart of the pulsar uncertain.

Reflected iron line from a source above a Kerr black hole accretion disc

Abstract: In this paper we present a fully relativistic approach to modelling both the continuum emission and the reflected fluorescent iron line from a primary X-ray source near a Kerr black hole. The X-ray source is located above an accretion disc orbiting around the black hole. The source is assumed to be a static point source located on an arbitrary position above the disc, on or off the axis of rotation. We carry out Monte Carlo simulations in order to estimate the iron line spectrum as well as its equivalent width. Because of the gravitational lensing effect, an enhancement of the iron line is expected when the primary source is located close to the central black hole. We find that for a source located on the axis of rotation the enhancement is relatively modest. An observer at inclination 30° would measure an equivalent width of ∼300 eV in the extreme case of a maximally rotating black hole and a source located at height 1.5 gravitational radii from the centre. This corresponds to an equivalent width enhancement factor of about 2 compared with the classical value where no lensing effect comes into play. However, when allowing the source to be located off the axis of rotation, much stronger enhancement can be obtained. In the extreme case of a maximally rotating black hole and a source located just above the approaching side of the disc, an observer at inclination 30° could measure an equivalent width as high as ∼1.5 keV (i.e., ∼10 times the classical value). We also find that observers located at high inclination angles observe a stronger line than observers at low inclination angles.

Analytical solutions for turbulent non-Boussinesq plumes

Abstract: Analytical solutions are developed for non-Boussinesq turbulent plumes rising from horizontal area sources in unconfined quiescent environments of uniform density. The approach adopted follows and extends an earlier approach for Boussinesq plumes and replaces the non-Boussinesq area source of interest and located at z=0 with an idealized point source located at a virtual origin z=z v such that the flow above the idealized source approximates that from the actual source. Asymptotic analytical expressions are developed for the location of the virtual source that are valid for large vertical distances above the non-Boussinesq source. The non-Boussinesq source is characterized by a non-dimensional parameter Γ nb which is a measure of the relative strengths of the mass, momentum and density deficit fluxes at, or at a specified height above, the source. The vertical distance between the actual and virtual sources scales on the length scale l that characterizes the height over which the flow is non-Boussinesq and expressions for z v /l are developed for lazy (Γ nb > 1) and forced plume (Γ ub < 1) sources. For pure-plume source conditions Γ nb = 1, and the virtual source provides an exact representation of the actual plume above z =0. The limiting cases of a nearly pure lazy plume and of a highly lazy plume are also explored analytically

Sound propagation from a point source over extended-reaction ground

Abstract: Through comparisons with numerical predictions, with data from laboratory experiments and with outdoor data obtained over snow, heuristic modifications of the classical analytical approximation for the field due to a point source above an impedance plane are shown to be adequate for predicting sound propagation from a point source close to layered porous media with extended reaction. The main deficiencies are for extremely low flow resistivities and at close ranges. It is shown that multiple layering offers a possible explanation for previously reported difficulties in obtaining theoretical fits to propagation data over snow [J. Acoust. Soc. Am. 77, 67–73 (1985)].