Showing papers on "Point source published in 2008"
TL;DR: In this article, a component separation challenge has been organized, based on a set of realistically complex simulations of sky emission, and several methods including those based on internal template subtraction, maximum entropy method, parametric method, spatial and harmonic cross correlation methods, and independent component analysis have been tested.
Abstract: Context. The PLANCK satellite will map the full sky at nine frequencies from 30 to 857 GHz. The CMB intensity and polarization that are its prime targets are contaminated by foreground emission.
Aims. The goal of this paper is to compare proposed methods for separating CMB from foregrounds based on their different spectral and spatial characteristics, and to separate the foregrounds into “components” with different physical origins (Galactic synchrotron, free-free and dust emissions; extra-galactic and far-IR point sources; Sunyaev-Zeldovich effect, etc.)
Methods. A component separation challenge has been organised, based on a set of realistically complex simulations of sky emission. Several methods including those based on internal template subtraction, maximum entropy method, parametric method, spatial and harmonic cross correlation methods, and independent component analysis have been tested.
Results. Different methods proved to be effective in cleaning the CMB maps of foreground contamination, in reconstructing maps of diffuse Galactic emissions, and in detecting point sources and thermal Sunyaev-Zeldovich signals. The power spectrum of the residuals is, on the largest scales, four orders of magnitude lower than the input Galaxy power spectrum at the foreground minimum. The CMB power spectrum was accurately recovered up to the sixth acoustic peak. The point source detection limit reaches 100 mJy, and about 2300 clusters are detected via the thermal SZ effect on two thirds of the sky. We have found that no single method performs best for all scientific objectives.
Conclusions. We foresee that the final component separation pipeline for PLANCK will involve a combination of methods and iterations between processing steps targeted at different objectives such as diffuse component separation, spectral estimation, and compact source extraction.
260 citations
TL;DR: In this article, a component separation challenge has been organized, based on a set of realistically complex simulations of sky emission, and several methods including those based on internal template subtraction, maximum entropy method, parametric method, spatial and harmonic cross correlation methods, and independent component analysis have been tested.
Abstract: The Planck satellite will map the full sky at nine frequencies from 30 to 857 GHz. The CMB intensity and polarization that are its prime targets are contaminated by foreground emission. The goal of this paper is to compare proposed methods for separating CMB from foregrounds based on their different spectral and spatial characteristics, and to separate the foregrounds into components of different physical origin. A component separation challenge has been organized, based on a set of realistically complex simulations of sky emission. Several methods including those based on internal template subtraction, maximum entropy method, parametric method, spatial and harmonic cross correlation methods, and independent component analysis have been tested. Different methods proved to be effective in cleaning the CMB maps from foreground contamination, in reconstructing maps of diffuse Galactic emissions, and in detecting point sources and thermal Sunyaev-Zeldovich signals. The power spectrum of the residuals is, on the largest scales, four orders of magnitude lower than that of the input Galaxy power spectrum at the foreground minimum. The CMB power spectrum was accurately recovered up to the sixth acoustic peak. The point source detection limit reaches 100 mJy, and about 2300 clusters are detected via the thermal SZ effect on two thirds of the sky. We have found that no single method performs best for all scientific objectives. We foresee that the final component separation pipeline for Planck will involve a combination of methods and iterations between processing steps targeted at different objectives such as diffuse component separation, spectral estimation and compact source extraction.
211 citations
TL;DR: In this article, the authors extended the approach of Georganopoulos, Kirk, and Mastichiadis (2001) to include external Compton processes and derived accurate Compton-scattered spectra throughout the Thomson and Klein-Nishina regimes for external Compton scattering.
Abstract: We extend a method for modeling synchrotron and synchrotron self-Compton radiations in blazar jets to include external Compton processes. The basic model assumption is that the blazar radio through soft X-ray flux is nonthermal synchrotron radiation emitted by isotropically-distributed electrons in the randomly directed magnetic field of outflowing relativistic blazar jet plasma. Thus the electron distribution is given by the synchrotron spectrum, depending only on the Doppler factor $\delta_{\rm D}$ and mean magnetic field $B$, given that the comoving emission region size scale $R_b^\prime \lesssim c \dD t_v/(1+z)$, where $t_v$ is variability time and $z$ is source redshift. Generalizing the approach of Georganopoulos, Kirk, and Mastichiadis (2001) to arbitrary anisotropic target radiation fields, we use the electron spectrum implied by the synchrotron component to derive accurate Compton-scattered $\gamma$-ray spectra throughout the Thomson and Klein-Nishina regimes for external Compton scattering processes. We derive and calculate accurate $\gamma$-ray spectra produced by relativistic electrons that Compton-scatter (i) a point source of radiation located radially behind the jet, (ii) photons from a thermal Shakura-Sunyaev accretion disk and (iii) target photons from the central source scattered by a spherically-symmetric shell of broad line region (BLR) gas. Calculations of broadband spectral energy distributions from the radio through $\gamma$-ray regimes are presented, which include self-consistent $\gamma\gamma$ absorption on the same radiation fields that provide target photons for Compton scattering. Application of this baseline flat spectrum radio/$\gamma$-ray quasar model is considered in view of data from $\gamma$-ray telescopes and contemporaneous multi-wavelength campaigns.
190 citations
TL;DR: It is demonstrated that a quasi-crystal array of nanoholes in a metal screen can mimic a function of the lens: one-to-one imaging of a point source located a few tens of wavelengths away from the array to a point on the other side of the array.
Abstract: We demonstrate that a quasi-crystal array of nanoholes in a metal screen can mimic a function of the lens: one-to-one imaging of a point source located a few tens of wavelengths away from the array to a point on the other side of the array. A displacement of the point source leads to a linear displacement of the image point. Complex structures composed of multiple point sources can be faithfully imaged with resolutions comparable to those of high numerical aperture lenses.
172 citations
TL;DR: In this article, an unbinned likelihood ratio method is applied to search for high energy point-like neutrino sources using detectors deep in the ice or sea, based on real world performance of existing detectors such as AMANDA, IceCube, and ANTARES.
167 citations
TL;DR: In this article, a semi-empirical simulation of the extragalactic radio continuum sky is presented for aiding the design of next generation radio interferometers such as the SKA.
Abstract: We have developed a semi-empirical simulation of the extragalactic radio continuum sky suitable for aiding the design of next generation radio interferometers such as the Square Kilometre Array (SKA). The emphasis is on modelling the large-scale cosmological distribution of radio sources rather than the internal details of individual galaxies. Here we provide a description of the simulation to accompany the online release of a catalogue of 320 million simulated radio sources. The simulation covers 20x20 deg^2 - a plausible upper limit to the instantaneous field of view attainable with future (e.g. SKA) aperture array technologies - out to redshift z=20, and down to flux density limits of 10 nJy at 151, 610 MHz, 1.4, 4.86 and 18 GHz. Five distinct source types are included: radio-quiet AGN, radio-loud AGN of the FRI and FRII structural classes, and star-forming galaxies, the latter split into populations of quiescent and starbursting galaxies.
In our semi-empirical approach, the simulated sources are drawn from observed (or extrapolated) luminosity functions and grafted onto an underlying dark matter density field with biases which reflect their measured large-scale clustering. A numerical Press-Schechter-style filtering of the density field is used to identify and populate clusters of galaxies. Radio source structures are built from point source and elliptical sub-components, and for FRI and FRII sources an orientation-based unification and beaming model is used to partition flux between the core and extended lobes and hotspots. The simulation output can be post-processed to achieve more complete agreement with observational data in the years ahead, with the aim of using these 'idealised skies' in telescope simulators to optimise the design of the SKA itself (abridged).
144 citations
TL;DR: In this paper, the authors obtained and analyzed Chandra ACIS-S observations of the strongly accreting T Tauri star DG Tau, and extracted separate X-ray spectra for DG Tau and areas outside its point spread function.
Abstract: Aims. We have obtained and analyzed Chandra ACIS-S observations of the strongly accreting classical T Tauri star DG Tau. Our principal goals are to map the immediate environment of the star to characterize possible extended X-rays formed in the jet, and to re-visit the anomalous, doubly absorbed X-ray spectrum of DG Tau itself. Methods. We combine our new ACIS-S data with a data set obtained previously. The data are superimposed to obtain flux and hardness images. Separate X-ray spectra are extracted for DG Tau and areas outside its point spread function. Results. We detect a prominent X-ray jet at a position angle of PA ≈ 225 deg (tentatively suggested by Gudel et al. 2005, ApJ, 626, L53), coincident with the optical jet axis. We also identify a counter jet at PA = 45 deg. The X-ray jets are detected out to a distance of ≈5 �� from the star, their sources being extended at the ACIS-S resolution. The jet spectra are soft, with a best-fit electron temperature of 3.4 MK. We find evidence for excess absorption of the counter jet. The spectrum of the DG Tau point source shows two components with largely different temperatures and absorption column densities. Conclusions. The similar temperatures and small absorbing gas columns of the jet sources and the soft component of the “stellar” source suggest that these sources are related, produced either by shocks or by magnetic heating in the jets. Cooling estimates suggest that the pressure in the hot gas contributes to jet expansion. The hard “stellar” component, on the other hand, is associated with a stellar corona or magnetosphere. The excessive photoelectric absorption of this component suggests the presence of dust-depleted accretion streams above coronal magnetic fields.
120 citations
107 citations
TL;DR: In this article, the authors derived simultaneously an all-sky census of emitting sources and images of the Galactic Ridge (GR) emission, and compared the GR emission spatial distribution to those obtained from CO and NIR maps.
Abstract: We have processed the data accumulated with INTEGRAL SPI during 4 years (~ 51 Ms) to study the Galactic ``diffuse'' emission morphology in the 20 keV to 8 MeV energy range. To achieve this objective, we have derived simultaneously an all-sky census of emitting sources and images of the Galactic Ridge (GR) emission. In the central radian, the resolved point source emission amounts to 88%, 91% and 68% of the total emission in the 25-50, 50-100 and 100-300 keV domains respectively. We have compared the GR emission spatial distribution to those obtained from CO and NIR maps, and quantified our results through latitude and longitude profiles. Below 50 keV, the SPI data are better traced by the latter, supporting a stellar origin for this emission. Furthermore, we found that the GR emission spectrum follows a power law with a photon index ~ 1.55 above 50 keV while an additional component is required below this energy. This component shows a cutoff around 30 keV, reinforcing a stellar origin, as proposed by Krivonos et al. (2007). The annihilation diffuse emission component is extracted simultaneously, leading to the determination of the related parameters (positronium flux and fraction). A specific discussion is devoted to the annihilation line distribution since a significant emission is detected over a region as large as ~80 degrees by ~10 degrees potentially associated with the disk or halo surrounding the central regions of our Galaxy.
98 citations
TL;DR: In this paper, the authors reported the identification of a source coincident with the position of the nearby Type II-P supernova 2008bk in high-quality optical and near-infrared preexplosion images from the ESO Very Large Telescope (VLT).
Abstract: We report the identification of a source coincident with the position of the nearby Type II-P supernova (SN) 2008bk in high-quality optical and near-infrared preexplosion images from the ESO Very Large Telescope (VLT). The SN position in the optical and near-infrared preexplosion images is identified to within about ±70 and ±40 mas, respectively, using postexplosion Ks-band images obtained with the NAOS CONICA adaptive optics system on the VLT. The preexplosion source detected in four different bands is precisely coincident with SN 2008bk and is consistent with being dominated by a single point source. We determine the nature of the point source using the STARS stellar evolutionary models and find that its colors and luminosity are consistent with the source being a red supergiant progenitor of SN 2008bk with an initial mass of 8.5 ± 1.0 M☉.
TL;DR: In this article, the authors reported the identification of a source coincident with the position of the nearby type II-P supernova 2008bk in high quality optical and near-infrared pre-explosion images from the ESO Very Large Telescope (VLT).
Abstract: We report the identification of a source coincident with the position of the nearby type II-P supernova (SN) 2008bk in high quality optical and near-infrared pre-explosion images from the ESO Very Large Telescope (VLT). The SN position in the optical and near-infrared pre-explosion images is identified to within about +-70 and +-40 mas, respectively, using post-explosion Ks-band images obtained with the NAOS CONICA adaptive optics system on the VLT. The pre-explosion source detected in four different bands is precisely coincident with SN 2008bk and is consistent with being dominated by a single point source. We determine the nature of the point source using the STARS stellar evolutionary models and find that its colours and luminosity are consistent with the source being a red supergiant progenitor of SN 2008bk with an initial mass of 8.5 +- 1.0 Msun.
TL;DR: In this article, the benefits of using single timeslice stochastic sources for the calculation of light quark physics on the lattice were investigated, and it was found that the use of stochastically sources gives a considerable improvement in statistics for the same computational cost.
Abstract: In this paper we investigate the benefits of using (2)⊗(2) single timeslice stochastic sources for the calculation of light quark physics on the lattice. Meson 2-point correlators measured using sources stochastic in only spin and those stochastic in both spin and colour indices are compared to point source correlators on the unit gauge and on a 163 × 32 Domain Wall QCD ensemble. It is found that the use of stochastic sources gives a considerable improvement in statistics for the same computational cost. The neutral kaon mixing matrix element BK is also calculated on this ensemble with stochastic sources, but we conclude that the stochastic method offers no significant advantage over the traditional gauge-fixed wall source approach which already offers an exact volume average. We also discuss the application to semileptonic form factors in conjunction with partially twisted boundary conditions.
TL;DR: The whole proposed framework takes advantage of the capabilities of the preprocessing channel identification step and the new simple and accurate closed-form estimators to accurately retrieve the channel parameters even in the most adverse conditions.
Abstract: We propose a new two-stage approach to estimate the nominal angles of arrival (AoAs) and the angular spreads (ASs) of multiple locally scattered sources using a uniform linear array (ULA) of sensors. In contrast to earlier works, we consider both long- and short-term channel variations, typically encountered in wireless links. In the first stage, we exploit sources independence to blindly estimate the channel over several data blocks regularly spaced by intervals larger than the coherence time but each, short enough in length, to make time variations negligible within the block duration. We, thereby, decouple the multisource channel parameters estimation problem in hand into parallel and independent single-source channel parameters estimation subproblems. In the second stage, for each spatially scattered source, we process the corresponding sequence of quasi-independent channel realization estimates as a new single-scattered-source observation over which we apply Taylor series expansions to transform the estimation of the nominal AoA and the AS of the corresponding scattered source into a simple localization of two closely spaced, equi-powered, and uncorrelated rays (i.e., point sources). To localize both rays, we propose new accurate and computationally simple closed-form expressions for the mean value of the spatial harmonics and their separation by means of covariance fitting. An asymptotic performance analysis is also provided to prove the efficiency of the proposed estimators. Then, the AS and the nominal AoA of every source are directly deduced. The whole proposed framework takes advantage of the capabilities of the preprocessing channel identification step (to reduce the noise effect and decouple the estimation of the channel parameters of every source from the others) and the new simple and accurate closed-form estimators to accurately retrieve the channel parameters even in the most adverse conditions, mainly low signal-to-noise ratio (SNR), few sensors, no prior knowledge of the angular distribution, and closely spaced sources, as supported by simulations.
TL;DR: In this paper, the authors presented two wide field (≈ 5 ′ × 3.5 ′ ), diffraction limited (λ/D ≃ 0.5 ǫ at 10 m), broad-band 10 m and 20 m images of the Orion Nebula, plus six 7 −13 m narrow-band (λ /�λ ≃ 1) images taken at the 3.8m UKIRT 1 telescope with the MPIA MAX camera.
Abstract: We present two wide-field (≈ 5 ′ × 3.5 ′ ), diffraction limited (λ/D ≃ 0.5 ′′ at 10 � m), broad-band 10 � m and 20 � m images of the Orion Nebula, plus six 7–13 � m narrow-band (λ/�λ ≃ 1) images of the BN/KL complex taken at the 3.8m UKIRT 1 telescope with the MPIA MAX camera. The wide field images, centered on the Trapezium and BN/KL regions, are mosaics of 35 ′′ × 35 ′′ frames obtained with standard chopping and nodding technique and reconstructed using a new restoration method developed for this project. They show the filamentary structure of the dust emission from the walls of the HII region and reveal a new remarkable group of arc-like structures ≈ 1 ′ to the South of the Trapezium. The morphology of the Ney-Allen nebula, produced by wind-wind interaction in the vicinity of the Trapezium stars, suggests a complex kinematical structure at the center of the Cluster. We find indications that one of the most massive members of the cluster, the B0.5V star θ 1 Ori-D, is surrounded by a photoevaporated circumstellar disk. Among the four historic Trapezium OB stars, this is the only one without a binary companion, suggesting that stellar multiplicity and the presence of massive circumstellar disks may be mutually exclusive. In what concerns the BN/KL complex, we find evidence for extended optically thin silicate emission on top of the deep 10 � m absorption feature. Assuming a simple two component model, we map with ≃ 0. 5 spatial resolution the foreground optical depth, color temperature and mid-IR luminosity of the embedded sources. We resolve a conspicuous point source at the location of the IRc2-A knot, approximately 0. 5 north of the deeply embedded HII region “I”. We analyze the spectral profile of the 10 � m silicate absorption feature and find indication for grain crystallization in the harsh nebular environment. In the OMC-1 South region, we detect several point sources and discuss their association with the mass loss phenomenology observed at optical and millimeter wavelengths. Finally, we list the position and photometry of 177 point sources, the large majority of which detected for the first time in the mid-IR. Twenty two of them lack a counterpart at shorter wavelengths, and are, therefore, candidates for deeply embedded protostars. The comparison of photometric data obtained at two different epochs reveals that source variability at 10 � m is present up to ≈ 1 mag level on a time-scale ∼ 2 yr. With the possible exception of a pair of OB stars, all point sources detected at shorter wavelengths display 10 � m emission well above the photospheric level, that we attribute to disks circumstellar emission. The model of Robberto, Beckwith, & Panagia (2002, ApJ. 578, 897) provides the simplest explanation for the observed mid-IR excess. Subject headings: nebulae: Orion Nebula, Infrared, ISM, Data Analysis — Infrared
TL;DR: In this article, the Rossi X-Ray Timing Explorer (RXTE) was used to detect 70.5 ms pulsations from the X-ray source AX J1838.0-0655, which coincides with an unresolved INTEGRAL source and the extended TeV source HESS J1837-069.
Abstract: We report the discovery of 70.5 ms pulsations from the X-ray source AX J1838.0–0655 using the Rossi X-Ray Timing Explorer ( RXTE). PSR J1838–0655 is a rotation-powered pulsar with spin-down luminosity Ė = 5.5 × 1036 ergs s−1, characteristic age τc ≡ P/2 = 23 kyr, and surface dipole magnetic field strength Bs = 1.9 × 1012 G. It coincides with an unresolved INTEGRAL source and the extended TeV source HESS J1837–069. At an assumed distance of 6.6 kpc by association with an adjacent massive star cluster, the efficiency of PSR J1838–0655 converting spin-down luminosity to radiation is 0.8% for the 2–10 keV ASCA flux, 9% for the 20–300 keV INTEGRAL flux and ~3% for the >200 GeV emission of HESS J1837–069, making it a plausible power source for the latter. A Chandra X-ray observation resolves AX J1838.0–0655 into a bright point source surrounded by a 2' diameter, centrally peaked nebula. The spectra of the pulsar and nebula are each well fitted by power laws, with photon indices Γ = 0.5(0.3–0.7) and Γ = 1.6(1.1–2.0) , respectively. The 2–10 keV X-ray luminosities of the pulsar and nebula are LPSR = 4.6 × 1034 d26.6 ergs s−1 and LPWN = 5.2 × 1033 d26.6 ergs s−1. A second X-ray source adjacent to the TeV emission, AX J1837.3–0652, is resolved into an apparent pulsar/PWN; it may also contribute to HESS J1837–069. The star cluster RSGC 1 may have given birth to one or both pulsars, while fueling TeV emission from the extended PWN with target photons for inverse Compton scattering.
TL;DR: In this article, the efficiency in source detection and flux density estimation of blind and non-blind detection techniques exploiting the MHW2 filter applied to the Wilkinson Microwave Anisotropy Probe (WMAP) 5-year maps is analyzed.
Abstract: We have analyzed the efficiency in source detection and flux density estimation of blind and non-blind detection techniques exploiting the MHW2 filter applied to the Wilkinson Microwave Anisotropy Probe (WMAP) 5-year maps. A comparison with the AT20G Bright Source Sample (Massardi et al. 2008), with a completeness limit of 0.5 Jy and accurate flux measurements at 20 GHz, close to the lowest frequency of WMAP maps, has allowed us to assess the completeness and the reliability of the samples detected with the two approaches, as well as the accuracy of flux and error estimates, and their variations across the sky. The uncertainties on flux estimates given by our procedure turned out to be about a factor of 2 lower than the rms differences with AT20G measurements, consistent with the smoothing of the fluctuation field yielded by map filtering. Flux estimates were found to be essentially unbiased except that, close to the detection limit, a substantial fraction of fluxes are found to be inflated by the contribution of underlying positive fluctuations. This is consistent with expectations for the Eddington bias associated to the true errors on flux density estimates. The blind and non-blind approaches are found to be complementary: each of them allows the detection of sources missed by the other. Combining results of the two methods on the WMAP 5-year maps we have expanded the non-blindly generated New Extragalactic WMAP Point Source (NEWPS) catalogue (Lopez-Caniego et al. 2007) that was based on WMAP 3-year maps. After having removed the probably spurious objects not identified with known radio sources, the new version of the NEWPS catalogue, NEWPS_5yr comprises 484 sources detected with a signal-to-noise ratio SNR>5.
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.
TL;DR: In this article, Monte Carlo solutions of the 3D radiative transfer (RT) equations for energy transport in elastic media with randomly fluctuating velocity and density were presented, including mode conversions from P -t oS-wave energy and vice versa and considering angular-dependent scattering patterns following from the Born approximation.
Abstract: SUMMARY We present Monte Carlo solutions of the 3-D radiative transfer (RT) equations for energy transport in elastic media with randomly fluctuating velocity and density. It includes mode conversions from P -t oS-wave energy and vice versa and considers angular-dependent scattering patterns following from the Born approximation. Synthesis of the space‐time distribution of seismic energy emitted from point sources with arbitrary radiation patterns can be achieved. The method offers a unique way to model complete mean square envelopes of high-frequency wavefields in the presence of random heterogeneity starting from the first P-wave onset until the late S-wave coda. Validation of the method is achieved through a comparison of mean square envelopes from an isotropic P-wave radiation point source with full 3-D wavefield simulations for the whole envelope shape and with the analytical Markov approximation for small lapse times. RT yields accurate envelope shapes even for parameter ranges where strong and direction-dependent scattering occurs. Peak amplitudes, envelope broadening and coda decay at long lapse times are correctly modelled. A breakdown of RT with Born scattering coefficients only occurs in the vicinity of a point source: waveform modelling shows that even for a pure compressional source, some per cent of shear wave energy are generated by near-source scattering that are not explained within the framework of Born approximation.
TL;DR: In this paper, spectral index distributions, number counts, redshift distribution and other general statistical properties of extragalactic point sources in the New Extragaleactic WMAP Point Source5σ (NEWPS) sample were compared with model predictions.
Abstract: We present results on spectral index distributions, number counts, redshift distribution and other general statistical properties of extragalactic point sources in the New Extragalactic WMAP Point Source5σ (NEWPS) sample. The flux calibrations at all the Wilkinson Microwave Anisotropy Probe channels have been reassessed both by comparison with ground-based observations and through estimates of the effective beam areas. The two methods yield consistent statistical correction factors. A search of the NASA Extragalactic Data base (NED) has yielded optical identifications for ∼89 per cent of sources in the complete subsample of 252 sources with signal-to-noise ratio (S/N) ≥ 5 and S≥ 1.1 Jy at 23 GHz; five sources turned out to be Galactic and were removed. The NED also yielded redshifts for ≃92 per cent of the extragalactic sources at |b| > 10°. Their distribution was compared with model predictions; the agreement is generally good but a possible discrepancy is noted. Using the 5 GHz fluxes from the GB6 or PMN surveys, we find that ∼76 per cent of the 191 extragalactic sources with S23 GHz > 1.3 Jy can be classified as flat-spectrum sources between 5 and 23 GHz. A spectral steepening is observed at higher frequencies: only 59 per cent of our sources are still flat-spectrum sources between 23 and 61 GHz, and the average spectral indexes steepen from 〈α235〉= 0.01 ± 0.03 to 〈α6141〉= 0.37 ± 0.03. We think, however, that the difference may be due to a selection effect. The source number counts have a close to Euclidean slope and are in good agreement with the predictions of the cosmological evolution model by De Zotti et al. The observed spectral index distributions were exploited to get model-independent extrapolations of counts to higher frequencies. The risks of such operations are discussed and reasons of discrepancies with other recent estimates are clarified.
TL;DR: In this article, the authors investigate the transient ventilation flow within a confined ventilated space, with high and low level openings, when the strength of a low-level point source of heat is changed instantaneously.
Abstract: We investigate the transient ventilation flow within a confined ventilated space, with high- and low-level openings, when the strength of a low-level point source of heat is changed instantaneously. The steady-flow regime in the space involves a turbulent buoyant plume, which rises from the point source to a well-mixed warm upper layer. The steady-state height of the interface between this layer and the lower layer of exterior fluid is independent of the heat flux, but the upper layer becomes progressively warmer with heat flux. New analogue laboratory experiments of the transient adjustment between steady states identify that if the heat flux is increased, the continuing plume propagates to the top of the room forming a new, warmer layer. This layer gradually deepens, and as the turbulent plume entrains fluid from the original warm layer, the original layer is gradually depleted and disappears, and a new steady state is established. In contrast, if the source buoyancy flux is decreased, the continuing plume is cooler than the original plume, so that on reaching the interface it is of intermediate density between the original warm layer and the external fluid. The plume supplies a new intermediate layer, which gradually deepens with the continuing flow. In turn, the original upper layer becomes depleted, both as a result of being vented through the upper opening of the space, but also due to some penetrative entrainment of this layer by the plume, as the plume overshoots the interface before falling back to supply the new intermediate layer. We develop quantitative models which are in good accord with our experimental data, by combining classical plume theory with models of the penetrative entrainment for the case of a decrease in heating. Typically, we find that the effect of penetrative entrainment on the density of the intruding layer is relatively weak, provided the change in source strength is sufficiently large. However, penetrative entrainment measurably increases the rate at which the depth of the draining layer decreases. We conclude with a discussion of the importance of these results for the control of naturally ventilated spaces.
TL;DR: An algorithm for detection and a subsequent information gain driven control of the observer for the purpose of parameter estimation of an unaccounted point source of relatively low-level gamma radiation.
TL;DR: In this paper, the authors analyzed the effect of point sources on the estimated strength of the non-Gaussianity in the cosmic microwave background (CMB) and showed that the biggest contribution comes from the cross correlation of the CMB with the matter density rather than from the Poisson term.
Abstract: In this paper we analyze the biasing effect of point sources, either thermal Sunyaev-Zeldovich clusters or standard radio sources, on the estimated strength of the non-Gaussianity in the cosmic microwave background (CMB). We show that the biggest contribution comes from the cross correlation of the CMB with the matter density rather than from the Poisson term which is conventionally assumed in these calculations. For the three year WMAP data, we estimate that point sources could produce a non-Gaussian signature equivalent to a bias in fNL of 0.35, 0.24, -0.097, -0.13 in the Ka, Q, V, and W bands, respectively. The level of bias we find is largely insufficient to explain the very high fNL values recently detected by Yadav and Wandelt. For Planck, we estimate the point source bispectra to contaminate the fNL estimator with a bias of 1.3, 0.34, -0.25, -0.48 at 30, 44, 70, 100 GHz, respectively. These results depend on the assumed redshift distribution of the point sources. However, given the projected Planck sensitivity of DeltafNL~=5 (95% C.L.), a good estimate of point sources' properties including their number density and redshift distribution is essential before deriving strong conclusions on primordial non-Gaussianity.
TL;DR: In this article, an advection-diffusion equation for a ground-level finite area source is solved analytically in a closed form using the superposition method, where power laws are assumed for height-dependent wind speed and vertical eddy diffusivity and for the downwind distance-dependent standard deviation of concentration distribution in the lateral direction.
TL;DR: In this article, the authors presented a 1.5deg x 8deg (220pc x 1195pc) multiband imaging photometer for Spitzer 24um image of the Galactic Center and an accompanying point source list.
Abstract: We present a 1.5deg x 8deg (220pc x 1195pc) Multiband Imaging Photometer for Spitzer 24um image of the Galactic Center and an accompanying point source list. This image is the highest spatial resolution (6" ~ 0.25pc) and sensitivity map ever taken across the GC at this wavelength, showing the emission by warm dust in unprecedented detail. Over 120,000 point sources are identified in this catalog with signal-to-noise ratios greater than five and flux densities from 0.6mJy to 9Jy.
TL;DR: In this paper, the expectation maximization algorithm was applied to the point source search in neutrino telescopes and the results in terms of minimum detectable number of events were compared advantageously with the results of a classical method with binning.
19 Sep 2008
TL;DR: A hybrid optimization scheme is proposed that generates reflector shapes for rotationally symmetric systems and an arbitrary source luminance distribution based on an extension of the traditional algorithm for a point source and a combination of an iterative algorithm and an optimization algorithm.
Abstract: Reflectors for prescribed intensity or illuminance distributions are commonly used in luminaires and automotive headlights. However, their design has remained a challenge. Although reflector shapes are well known for a point source, the point source approximation leads to significant errors in the output distribution with extended and nonuniform source distributions. In practice, source non-idealities usually require the use of automated and manual optimization in the design process. We propose a hybrid optimization scheme that generates reflector shapes for rotationally symmetric systems and an arbitrary source luminance distribution. This method is based on an extension of the traditional algorithm for a point source, and uses a combination of an iterative algorithm and an optimization algorithm. Several case studies are presented.
TL;DR: In this article, the authors reconstruct the electron wave front and show that the correct source-to-object distance can be determined by analyzing the focus of the reconstruction, based on which an object focus is located at the correct tip-toobject distance with a depth of sharpness of similar to 40 nm.
Abstract: Holography with the low energy electron point source (LEEPS) microscope has been explored for imaging of unstained biomolecules. DNA ropes are prepared on microfabricated sample supports and imaged with coherent 40 eV electrons emitted from a W(111) point source. We reconstruct the electron wave front and show that the correct source-to-object distance can be determined by analyzing the focus of the reconstruction. Upon variation of the source position. the reconstruction shows reproducible object features with an object focus located at the correct tip-to-object distance with a depth of sharpness of similar to 40 nm. It is argued that reconstruction artifacts can be identified by their focus behavior and that only features ill the first focus coming from the screen - truly relate to the object's structure.
TL;DR: In this paper, the authors used the compact mono-harmonic general solutions of transversely isotropic electro-magneto-thermo-elastic material to construct the three-dimensional Green's function for a steady point heat source on the surface of a semi-infinite transversely-isotropic EH material by five newly introduced monoharmonic functions.
TL;DR: In this paper, a new linear filtering technique, the so-called matched matrix filters, was proposed for simultaneous multi-frequency detection of extragalactic point sources in maps of the cosmic microwave background.
Abstract: In this work we address the problem of simultaneous multi-frequency detection of extragalactic point sources in maps of the Cosmic Microwave Background. We apply a new linear filtering technique, the so called `matched matrix filters', that incorporates full spatial information, including the cross-correlation among channels, without making any a priori assumption about the spectral behaviour of the sources. A substantial reduction of the background is achieved thanks to the optimal combination of filtered maps. We describe in detail the new technique and we apply it to the detection/estimation of radio sources in realistic all-sky Planck simulations at 30, 44, 70 and 100 GHz. Then we compare the results with the mono-frequential approach based on the standard matched filter, in terms of reliability, completeness and flux accuracy of the resulting point source catalogs. The new filters outperform the standard matched filters for all these indexes at 30, 44 and 70 GHz, whereas at 100 GHz both kind of filters have a similar performance. We find a noticeable increment of the number of true detections for a fixed reliability level. In particular, for a 95% reliability we practically double the number of detections at 30, 44 and 70 GHz.