Point source

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

Radiation resistance of elementary electric-current sources in a magnetoionic medium

Abstract: Integral expressions for the radiation resistances of a point source of electric current and a filament of finite length with a triangular current distribution are obtained for the case in which these sources are immersed in a loss-free and unbounded magnetoionic medium so that they are parallel to the direction of the magnetostatic field. The radiation resistance of the point source of electric current is found to become infinite in two frequency ranges, whose values are stated precisely, and this infinite behaviour is related to the medium resonances. It is found that, for the current filament, the radiation resistance remains finite for all frequencies except the upper hybrid resonant frequency. The reasons for the infinite behaviour of the radiation resistance at the upper hybrid resonant frequency are due to the limitations of the magnetoionic theory on which the present work is based. Numerical results for the radiation resistances of the two elementary electric-current sources are given for some typical values of the parameters of interest.

Chandra point-source counts in distant galaxy clusters

Abstract: Context. With the superb angular resolution of the Chandra Observatory, it is now possible to detect X‐ray point sources, either e mbedded in galaxy clusters or along the cluster line of sight, which cou ld not be resolved by previous instruments. This now allows studies of source counts in distant cluster fields. Aims. We want to analyze the inner region of clusters of galaxies to check for the presence of any overdensity of X-ray point sources embedded in the gas diffuse emission. These point sources are possible AGN belonging to the clusters and could contaminate the cluster emission. Methods. We used a sample of 18 distant (0.25 < z < 1.01) galaxy clusters from the Chandra archive to construct the log N− log S , in both the soft and hard energy bands, for the X‐ray point sources detected in the central cluster region to be compared with the counts of point sources detected in similarly deep fields without clusters. Results. We find a ∼ 2 � excess of cluster region sources at the bright end of the log N− log S . The radial distribution of the brightest X‐ray point sources confirms this excess and indicates that it is co nfined to the inner 0.5 Mpc of the cluster region. Conclusions. The results suggest the possible existence of X‐ray sources belonging to the cluster (most probably AGN, given their 0.5‐10 keV luminosity ranging from 10 43 to 10 44 erg s −1 ): on average one every three clusters. Unlike previous studies, which have mainly investigated the point-source population in the vicinity of the galaxy clust ers, the present study analyzes the content of point sources within the 1 Mpc region covered by the cluster extent. Our work confirms the findings o f other investigators who analyzed the central 1 Mpc region of more massive clusters and/or groups in a similar redshift range. The X‐ray source excess found here is much smaller than the excess of radio galaxies found recently in high-z X‐ray selected clusters, possibly due to the better sensitivity of the radio observations.

On the origin of tev gamma-ray emission from hess j1834–087

Abstract: We present an X-ray study of the field containing the extended TeV source HESS J1834–087 using data obtained with the XMM-Newton telescope. Previously, the coincidence of this source with both the shell-type supernova remnant (SNR) W41 and a giant molecular cloud (GMC) was interpreted as favoring π0-decay γ-rays from interaction of the old SNR with the GMC. Alternatively, the TeV emission has been attributed to inverse Compton scattering from leptons deposited by PSR J1833–0827, a pulsar assumed to have been born in W41 but now located 24' from the center of the SNR (and the TeV source). Instead, we argue for a third possibility, that the TeV emission is powered by a previously unknown pulsar wind nebula located near the center of W41. The candidate pulsar is XMMU J183435.3–084443, a hard X-ray point source that lacks an optical counterpart to R > 21 and is coincident with diffuse X-ray emission. The X-rays from both the point source and diffuse feature are evidently nonthermal and highly absorbed. A best-fit power-law model yields photon index Γ ~ 0.2 and Γ ~ 1.9, for the point source and diffuse emission, respectively, and 2-10 keV flux ≈5 × 10–13 erg cm–2 s–1 for each. At the measured 4 kpc distance of W41, the observed X-ray luminosity implies an energetic pulsar with erg s–1, which is also sufficient to generate the observed γ-ray luminosity of 2.7 × 1034 d 2 4 erg s–1 via inverse Compton scattering.