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Point source

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


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Journal ArticleDOI
TL;DR: In this article, the authors performed an extensive study of the non-poissonian template fitting (NPTF) on simulated data, exploring its ability to recover the flux and luminosity function of unresolved sources at the Galactic Center.
Abstract: The Galactic Center Excess (GCE) of GeV gamma rays can be explained as a signal of annihilating dark matter or of emission from unresolved astrophysical sources, such as millisecond pulsars. Evidence for the latter is provided by a statistical procedure---referred to as Non-Poissonian Template Fitting (NPTF)---that distinguishes the smooth distribution of photons expected for dark matter annihilation from a "clumpy" photon distribution expected for point sources. In this paper, we perform an extensive study of the NPTF on simulated data, exploring its ability to recover the flux and luminosity function of unresolved sources at the Galactic Center. When astrophysical background emission is perfectly modeled, we find that the NPTF successfully distinguishes between the dark matter and point source hypotheses when either component makes up the entirety of the GCE. When the GCE is a mixture of dark matter and point sources, the NPTF may fail to reconstruct the correct contribution of each component. We further study the impact of mismodeling the Galactic diffuse backgrounds, finding that while a dark matter signal could be attributed to point sources in some outlying cases for the scenarios we consider, the significance of a true point source signal remains robust. Our work enables us to comment on a recent study by Leane and Slatyer (2019) that questions prior NPTF conclusions because the method does not recover an artificial dark matter signal injected on actual Fermi data. We demonstrate that the failure of the NPTF to extract an artificial dark matter signal can be natural when point sources are present in the data---with the effect further exacerbated by the presence of diffuse mismodeling---and does not on its own invalidate the conclusions of the NPTF analysis in the Inner Galaxy.

43 citations

Journal ArticleDOI
TL;DR: In this paper, the radio source 53W002, a compact narrow-line galaxy at z = 2.390 from the Leiden-Berkeley Deep Survey, was detected using the Hubble Space Telescope/Planetary Camera images at ~006 FWHM resolution in the filters B450, V606 and I814.
Abstract: We present deep 63-orbit Hubble Space Telescope/Planetary Camera images at ~006 FWHM resolution in the filters B450, V606, and I814—as well as in redshifted Lyα—of the radio source 53W002, a compact narrow-line galaxy at z = 2.390 from the Leiden-Berkeley Deep Survey. These images allow us to distinguish several morphological components: (1) an unresolved nuclear point source (500 pc at z=2.390 for H0=75, q0 = 0), likely the central active galactic nucleus (AGN) that contains 20%-25% of the total light in BVI; (2) a compact continuum core (re 005); (3) a more extended envelope with an r1/4-like light profile and re 025 (~2 kpc); (4) two blue "clouds" roughly colinear across the nucleus, aligned with the radio source axis and contained well within the size of the radio source. The (B-I) color maps may suggest a narrow dust lane crossing between the nucleus and the smaller blue cloud. The radio source is not smaller than the distance between the blue continuum clouds and coincides with a bright Lyα "arc" in the western cloud, suggesting that jet-induced star formation could cause both blue clouds, except the outer parts of the western cloud. The shape of this larger blue cloud suggests reflected AGN continuum light shining through a cone (plus reradiated Lyα in emission). The Owens Valley Radio Observatory interferometric CO detection (Scoville et al.) on both sides of 53W002—and in the same direction as the continuum clouds and the radio jet—also suggests a star-bursting region induced by its radio jet, at least in the inner parts. Hence, both mechanisms likely play a role in the "alignment effect." Even at radio powers ~1.5 dex fainter than the 3CR sources, we thus find many of the same aligned features and complex morphology, although at much smaller angular scales and lower optical-UV luminosities. We discuss the consequences for 53W002's formation in the context of the 16 subgalactic objects at z2.40 around 53W002 (Pascarelle et al.).

43 citations

Journal ArticleDOI
TL;DR: In this paper, Bertolotti et al. applied a spectral approach to the theory of partial coherence of nonstationary light and applied it to the study of spatial coherence properties of non-stationary wave fields on propagation in free space.
Abstract: A spectral approach to the theory of partial coherence of nonstationary light [ M. Bertolotti , Pure Appl. Opt.6, 153 (1997)] is applied to the study of spatial coherence properties of nonstationary wave fields on propagation in free space. Three types of nonstationary light sources are considered—a point source, a spatially incoherent source, and a uniformly coherent source, the last being perfectly coherent in both space–time and space–frequency domains. An example of the diffraction pattern from a slit with nonstationary partially coherent illumination is used to illustrate the general discussion.

43 citations

Book ChapterDOI
TL;DR: In this article, a hybrid method for treating the seismic wave fields at localized 2D near-surface structures embedded in a 1D background medium, and excited by a point source is presented.
Abstract: Any calculation of seismic wave propagation comprising the seismic source, the travel path, and the receiver site in a single finite-difference (FD) model requires a considerable amount of computer time and memory. Moreover, the methods currently available for including point sources in the 2D FD calculations are far-field approximations only. Therefore we have developed a new hybrid method for treating the seismic wave fields at localized 2D near-surface structures embedded in a 1D background medium, and excited by a point source. The source radiation and propagation in the background model is solved by the discrete-wave number (DW) method, while the propagation in the local 2D structure is calculated by the FD method. The coupling between the two sets of calculations is performed on a rectangular excitation box surrounding the local structure. We show the usefulness of the method in ground-motion studies where both near-field source effects and local site effects are important. Technical problems connected with the inconsistency between the 3D source radiation and the 2D FD calculation are minor for the relatively distant in-plane point explosive sources, but are more serious for the in-plane dislocation sources.

43 citations

Journal ArticleDOI
TL;DR: In this article, Chandra X-ray Observatory ACIS-S3 imaging observations and VLT/FORS2 and Hubble Space Telescope optical observations of two low-density Galactic globular clusters; NGC 6366 and M 55 are presented.
Abstract: We present Chandra X-ray Observatory ACIS-S3 X-ray imaging observations and VLT/FORS2 and Hubble Space Telescope optical observations of two low-density Galactic globular clusters; NGC 6366 and M 55. We detect 16 X-ray sources with 0.5–6.0 keV luminosities above LX = 4 × 10 30 erg s −1 within the half-mass radius of M 55, of which 8 or 9 are expected to be background sources, and 5 within the half-mass radius of NGC 6366, of which 4 are expected to be background sources. Optical counterparts are identified for several X-ray sources in both clusters and from these we conclude that 3 of the X-ray sources in M 55 and 2 or 3 of the X-ray sources in NGC 6366 are probably related to the cluster. Combining these results with those for other clusters, we find the best fit for a predicted number of X-ray sources in a globular cluster μc = 1.2 Γ+ 1.1 Mh ,w hereΓ is the collision number and Mh is (half of) the cluster mass, both normalized to the values for the globular cluster M4. Some sources tentatively classified as magnetically active binaries are more luminous in X-rays than the upper limit of LX � 0.001 Lbol of such binaries in the solar neighbourhood. Comparison with XMM and ROSAT observations lead us to conclude that the brightest X-ray source in M 55, a dwarf nova, becomes fainter in X-rays during the optical outburst, in accordance with other dwarf novae. The brightest X-ray source in NGC 6366 is a point source surrounded by a slightly offset extended source. The absence of galaxies and Hα emission in our optical observations argues against a cluster of galaxies and against a planetary nebula, and we suggest that the source may be an old nova.

43 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202350
2022133
2021103
2020135
2019123
2018133