The Experts below are selected from a list of 375708 Experts worldwide ranked by ideXlab platform
Craig O Heinke - One of the best experts on this subject based on the ideXlab platform.
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a hydrogen atmosphere Spectral Model applied to the neutron star x7 in the globular cluster 47 tucanae
The Astrophysical Journal, 2006Co-Authors: Ramesh Narayan, Craig O Heinke, George B Rybicki, Jonathan E GrindlayAbstract:Current X-ray missions are providing high-quality X-ray spectra from neutron stars (NSs) in quiescent low-mass X-ray binaries (qLMXBs). This has motivated us to calculate new hydrogen atmosphere Models, including opacity due to free-free absorption and Thomson scattering, thermal electron conduction, and self-irradiation by photons from the compact object. We have constructed a self-consistent grid of neutron star Models covering a wide range of surface gravities, as well as effective temperatures, which we make available to the scientific community. We present multiepoch Chandra X-ray observations of the qLMXB X7 in the globular cluster 47 Tuc, which is remarkably nonvariable on timescales from minutes to years. Its high-quality X-ray spectrum is adequately fitted by our hydrogen atmosphere Model without any hard power-law component or narrow Spectral features. If a mass of 1.4 M☉ is assumed, our Spectral fits require that its radius be in the range Rns = 14.5 km (90% confidence), which is larger than that expected from currently preferred Models of NS interiors. If its radius is assumed to be 10 km, then a mass of Mns = 2.20 M☉ is required. Using Models with the appropriate surface gravity for each value of the mass and radius becomes important for interpretation of the highest quality data.
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a hydrogen atmosphere Spectral Model applied to the neutron star x7 in the globular cluster 47 tucanae
arXiv: Astrophysics, 2005Co-Authors: Craig O Heinke, Ramesh Narayan, George B Rybicki, Jonathan E GrindlayAbstract:Current X-ray missions are providing high-quality X-ray spectra from neutron stars (NSs) in quiescent low-mass X-ray binaries (qLMXBs). This has motivated us to calculate new hydrogen-atmosphere Models, including opacity due to free-free absorption and Thomson scattering, thermal electron conduction, and self-irradiation by photons from the compact object. We have constructed a self-consistent grid of neutron star Models covering a wide range of surface gravities as well as effective temperatures, which we make available to the scientific community. We present multi-epoch Chandra X-ray observations of the qLMXB X7 in the globular cluster 47 Tuc, which is remarkably nonvariable on timescales from minutes to years. Its high-quality X-ray spectrum is adequately fit by our hydrogen-atmosphere Model without any hard power-law component or narrow Spectral features. If a mass of 1.4 Msol is assumed, our Spectral fits require that its radius be in the range R=14.5^{+1.8}_{-1.6} km (90% confidence), larger than expected from currently preferred Models of NS interiors. If its radius is assumed to be 10 km, then a mass of M=2.20^{+0.03}_{-0.16} Msol is required. Using Models with the appropriate surface gravity for each value of the mass and radius becomes important for interpretation of the highest quality data.
Jonathan E Grindlay - One of the best experts on this subject based on the ideXlab platform.
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a hydrogen atmosphere Spectral Model applied to the neutron star x7 in the globular cluster 47 tucanae
The Astrophysical Journal, 2006Co-Authors: Ramesh Narayan, Craig O Heinke, George B Rybicki, Jonathan E GrindlayAbstract:Current X-ray missions are providing high-quality X-ray spectra from neutron stars (NSs) in quiescent low-mass X-ray binaries (qLMXBs). This has motivated us to calculate new hydrogen atmosphere Models, including opacity due to free-free absorption and Thomson scattering, thermal electron conduction, and self-irradiation by photons from the compact object. We have constructed a self-consistent grid of neutron star Models covering a wide range of surface gravities, as well as effective temperatures, which we make available to the scientific community. We present multiepoch Chandra X-ray observations of the qLMXB X7 in the globular cluster 47 Tuc, which is remarkably nonvariable on timescales from minutes to years. Its high-quality X-ray spectrum is adequately fitted by our hydrogen atmosphere Model without any hard power-law component or narrow Spectral features. If a mass of 1.4 M☉ is assumed, our Spectral fits require that its radius be in the range Rns = 14.5 km (90% confidence), which is larger than that expected from currently preferred Models of NS interiors. If its radius is assumed to be 10 km, then a mass of Mns = 2.20 M☉ is required. Using Models with the appropriate surface gravity for each value of the mass and radius becomes important for interpretation of the highest quality data.
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a hydrogen atmosphere Spectral Model applied to the neutron star x7 in the globular cluster 47 tucanae
arXiv: Astrophysics, 2005Co-Authors: Craig O Heinke, Ramesh Narayan, George B Rybicki, Jonathan E GrindlayAbstract:Current X-ray missions are providing high-quality X-ray spectra from neutron stars (NSs) in quiescent low-mass X-ray binaries (qLMXBs). This has motivated us to calculate new hydrogen-atmosphere Models, including opacity due to free-free absorption and Thomson scattering, thermal electron conduction, and self-irradiation by photons from the compact object. We have constructed a self-consistent grid of neutron star Models covering a wide range of surface gravities as well as effective temperatures, which we make available to the scientific community. We present multi-epoch Chandra X-ray observations of the qLMXB X7 in the globular cluster 47 Tuc, which is remarkably nonvariable on timescales from minutes to years. Its high-quality X-ray spectrum is adequately fit by our hydrogen-atmosphere Model without any hard power-law component or narrow Spectral features. If a mass of 1.4 Msol is assumed, our Spectral fits require that its radius be in the range R=14.5^{+1.8}_{-1.6} km (90% confidence), larger than expected from currently preferred Models of NS interiors. If its radius is assumed to be 10 km, then a mass of M=2.20^{+0.03}_{-0.16} Msol is required. Using Models with the appropriate surface gravity for each value of the mass and radius becomes important for interpretation of the highest quality data.
Hannming Henry Juang - One of the best experts on this subject based on the ideXlab platform.
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implementation of prognostic cloud scheme for a regional Spectral Model
Monthly Weather Review, 1998Co-Authors: Songyou Hong, Hannming Henry Juang, Qingyu ZhaoAbstract:The purpose of this study is to develop a precipitation physics package for the National Centers for Environmental Prediction (NCEP) Regional Spectral Model (RSM) designed to improve the skill of precipitation forecasts. The package incorporates a prognostic grid-resolvable precipitation scheme and a subgrid-scale precipitation parameterization scheme with a convective trigger that explicitly couples boundary layer and convective precipitation processes. In this paper, the implementation of a prognostic cloud scheme for the NCEP RSM is described. A subgrid-scale precipitation parameterization scheme was described in a companion paper. Dynamical processes such as advection and diffusion processes for liquid species are included. Eleven experiments are conducted with a grid spacing of approximately 25 km for a heavy rain case over the United States during 15‐17 May 1995. Special attention is given to the setup of the prognostic grid-resolvable precipitation scheme on a Spectral grid as well as the importance of dynamical processes on a mesoscale grid together with radiation feedback. Different prognostic cloud schemes, classified according to the number of predicted liquid species, are also compared.
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the nmc nested regional Spectral Model
Monthly Weather Review, 1994Co-Authors: Hannming Henry Juang, Masao KanamitsuAbstract:Abstract A nested primitive equation regional Spectral Model is developed. The Model consists of two components—a low-resolution global Spectral Model and a high-resolution regional Spectral Model. The two components have identical vertical structure and physical processes. The global Model component is a low-resolution version of the operational National Meteorological Center (NMC) global Spectral Model and uses spherical harmonics as horizontal basis functions. The regional Spectral Model component is a primitive equation Model on a stereographic projection and uses sine-cosine series as horizontal basis functions. The feature of the regional component is that it predicts deviations from the forecast of the global Model component, first proposed by Hoyer. A semi-implicit time scheme, time filtering, initialization, and horizontal diffusion are applied to these deviations in the regional domain. Several sensitivity experiments on “nesting periods,” lateral boundary treatments, and different global Model ...
Masao Kanamitsu - One of the best experts on this subject based on the ideXlab platform.
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the nmc nested regional Spectral Model
Monthly Weather Review, 1994Co-Authors: Hannming Henry Juang, Masao KanamitsuAbstract:Abstract A nested primitive equation regional Spectral Model is developed. The Model consists of two components—a low-resolution global Spectral Model and a high-resolution regional Spectral Model. The two components have identical vertical structure and physical processes. The global Model component is a low-resolution version of the operational National Meteorological Center (NMC) global Spectral Model and uses spherical harmonics as horizontal basis functions. The regional Spectral Model component is a primitive equation Model on a stereographic projection and uses sine-cosine series as horizontal basis functions. The feature of the regional component is that it predicts deviations from the forecast of the global Model component, first proposed by Hoyer. A semi-implicit time scheme, time filtering, initialization, and horizontal diffusion are applied to these deviations in the regional domain. Several sensitivity experiments on “nesting periods,” lateral boundary treatments, and different global Model ...
Johannes Buchner - One of the best experts on this subject based on the ideXlab platform.
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new Spectral Model for constraining torus covering factors from broadband x ray spectra of active galactic nuclei
The Astrophysical Journal, 2018Co-Authors: M Balokovic, M Brightman, F A Harrison, A Comastri, C Ricci, Johannes BuchnerAbstract:The basic unified Model of active galactic nuclei (AGNs) invokes an anisotropic obscuring structure, usually referred to as a torus, to explain AGN obscuration as an angle-dependent effect. We present a new grid of X-ray Spectral templates based on radiative transfer calculations in neutral gas in an approximately toroidal geometry, appropriate for CCD-resolution X-ray spectra (FWHM ≥ 130 eV). Fitting the templates to broadband X-ray spectra of AGNs provides constraints on two important geometrical parameters of the gas distribution around the supermassive black hole: the average column density and the covering factor. Compared to the currently available Spectral templates, our Model is more flexible, and capable of providing constraints on the main torus parameters in a wider range of AGNs. We demonstrate the application of this Model using hard X-ray spectra from NuSTAR (3–79 keV) for four AGNs covering a variety of classifications: 3C 390.3, NGC 2110, IC 5063, and NGC 7582. This small set of examples was chosen to illustrate the range of possible torus configurations, from disk-like to sphere-like geometries with column densities below, as well as above, the Compton-thick threshold. This diversity of torus properties challenges the simple assumption of a standard geometrically and optically thick toroidal structure commonly invoked in the basic form of the unified Model of AGNs. Finding broad consistency between our constraints and those from infrared Modeling, we discuss how the approach from the X-ray band complements similar measurements of AGN structures at other wavelengths.
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new Spectral Model for constraining torus covering factors from broadband x ray spectra of active galactic nuclei
arXiv: High Energy Astrophysical Phenomena, 2018Co-Authors: M Balokovic, M Brightman, F A Harrison, A Comastri, C Ricci, Johannes BuchnerAbstract:The basic unified Model of active galactic nuclei (AGN) invokes an anisotropic obscuring structure, usually referred to as a torus, to explain AGN obscuration as an angle-dependent effect. We present a new grid of X-ray Spectral templates based on radiative transfer calculations in neutral gas in an approximately toroidal geometry, appropriate for CCD-resolution X-ray spectra (FWHM > 130 eV). Fitting the templates to broadband X-ray spectra of AGN provides constraints on two important geometrical parameters of the gas distribution around the supermassive black hole: the average column density and the covering factor. Compared to the currently available Spectral templates, our Model is more flexible, and capable of providing constraints on the main torus parameters in a wider range of AGN. We demonstrate the application of this Model using hard X-ray spectra from NuSTAR (3-79 keV) for four AGN covering a variety of classifications: 3C 390.3, NGC 2110, IC 5063, and NGC 7582. This small set of examples was chosen to illustrate the range of possible torus configurations, from disk-like to sphere-like geometries with column densities below, as well as above, the Compton-thick threshold. This diversity of torus properties challenges the simple assumption of a standard geometrically and optically thick toroidal structure commonly invoked in the basic form of the unified Model of AGN. Finding broad consistency between the our constraints and those from infrared Modeling, we discuss how the approach from the X-ray band complements similar measurements of AGN structures at other wavelengths.
