The Experts below are selected from a list of 5274 Experts worldwide ranked by ideXlab platform
E Tempel - One of the best experts on this subject based on the ideXlab platform.
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Fermi-LAT gamma-ray signal from Earth Limb, systematic detector effects and their implications for the 130 GeV gamma-ray excess
The European Physical Journal C, 2013Co-Authors: A Hektor, M Raidal, E TempelAbstract:We look for possible spectral features and systematic effects in the Fermi LAT publicly available high-energy gamma-ray data by studying photons from the Galactic center, nearby galaxy clusters, nearby brightest galaxies, AGNs, unassociated sources, hydrogen clouds and from the Earth Limb. Apart from the already known 130 GeV gamma-ray excesses from the first two sources, we find no statistically significant excesses from any of the cosmological sources nor from any control region. Therefore our main effort goes to the study of gamma rays appearing from the Earth Limb. In the energy range of 30 to 200 GeV the Earth Limb gamma-ray spectrum follows a power-law with spectral index 2.86±0.05 at 95 % CL, in a good agreement with the PAMELA measurement of the cosmic ray proton spectral index of 2.82–2.85, confirming the physical origin of the Limb gamma-rays. In subsets of the Earth Limb data at small photon incidence angle spectral features occur, including a feature at 130 GeV. We observe a systematic ∼2 σ -level difference in the Earth Limb spectra with small and large incidence angles. The behavior of those spectral features as well as the background indicates that those may be statistical fluctuations or complicated unknown systematic effects of the Fermi LAT. In the latter case, only the Fermi LAT Collaboration can give the final answer having access to raw data and all details of the reconstruction.
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fermi lat gamma ray signal from Earth Limb systematic detector effects and their implications for the 130 gev gamma ray excess
arXiv: High Energy Astrophysical Phenomena, 2012Co-Authors: A Hektor, M Raidal, E TempelAbstract:We look for possible spectral features and systematic effects in Fermi-LAT publicly available high-energy gamma-ray data by studying photons from the Galactic centre, nearby galaxy clusters, nearby brightest galaxies, AGNs, unassociated sources, hydrogen clouds and Earth Limb. Apart from already known 130 GeV gamma-ray excesses from the first two sources, we find no new statistically significant signal from others. Much of our effort goes to studying Earth Limb photons. In the energy range 30 GeV to 200 GeV the Earth Limb gamma-ray spectrum follows power-law with spectral index 2.87\pm 0.04 at 95 % CL, in a good agreement with the PAMELA measurement of cosmic ray proton spectral index between 2.82-2.85, confirming the physical origin of the Limb gamma-rays. In small subsets of Earth Limb data with small photon incidence angle it is possible to obtain spectral features at different energies, including at 130 GeV, but determination of background, thus their significances, has large uncertainties in those cases. We observe systematic 2\sigma level differences in the Earth Limb spectra of gamma-rays with small and large incidence angles. The behaviour of those spectral features as well as background indicates that they are likely statistical fluctuations.
A Hektor - One of the best experts on this subject based on the ideXlab platform.
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Fermi-LAT gamma-ray signal from Earth Limb, systematic detector effects and their implications for the 130 GeV gamma-ray excess
The European Physical Journal C, 2013Co-Authors: A Hektor, M Raidal, E TempelAbstract:We look for possible spectral features and systematic effects in the Fermi LAT publicly available high-energy gamma-ray data by studying photons from the Galactic center, nearby galaxy clusters, nearby brightest galaxies, AGNs, unassociated sources, hydrogen clouds and from the Earth Limb. Apart from the already known 130 GeV gamma-ray excesses from the first two sources, we find no statistically significant excesses from any of the cosmological sources nor from any control region. Therefore our main effort goes to the study of gamma rays appearing from the Earth Limb. In the energy range of 30 to 200 GeV the Earth Limb gamma-ray spectrum follows a power-law with spectral index 2.86±0.05 at 95 % CL, in a good agreement with the PAMELA measurement of the cosmic ray proton spectral index of 2.82–2.85, confirming the physical origin of the Limb gamma-rays. In subsets of the Earth Limb data at small photon incidence angle spectral features occur, including a feature at 130 GeV. We observe a systematic ∼2 σ -level difference in the Earth Limb spectra with small and large incidence angles. The behavior of those spectral features as well as the background indicates that those may be statistical fluctuations or complicated unknown systematic effects of the Fermi LAT. In the latter case, only the Fermi LAT Collaboration can give the final answer having access to raw data and all details of the reconstruction.
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fermi lat gamma ray signal from Earth Limb systematic detector effects and their implications for the 130 gev gamma ray excess
arXiv: High Energy Astrophysical Phenomena, 2012Co-Authors: A Hektor, M Raidal, E TempelAbstract:We look for possible spectral features and systematic effects in Fermi-LAT publicly available high-energy gamma-ray data by studying photons from the Galactic centre, nearby galaxy clusters, nearby brightest galaxies, AGNs, unassociated sources, hydrogen clouds and Earth Limb. Apart from already known 130 GeV gamma-ray excesses from the first two sources, we find no new statistically significant signal from others. Much of our effort goes to studying Earth Limb photons. In the energy range 30 GeV to 200 GeV the Earth Limb gamma-ray spectrum follows power-law with spectral index 2.87\pm 0.04 at 95 % CL, in a good agreement with the PAMELA measurement of cosmic ray proton spectral index between 2.82-2.85, confirming the physical origin of the Limb gamma-rays. In small subsets of Earth Limb data with small photon incidence angle it is possible to obtain spectral features at different energies, including at 130 GeV, but determination of background, thus their significances, has large uncertainties in those cases. We observe systematic 2\sigma level differences in the Earth Limb spectra of gamma-rays with small and large incidence angles. The behaviour of those spectral features as well as background indicates that they are likely statistical fluctuations.
M Raidal - One of the best experts on this subject based on the ideXlab platform.
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Fermi-LAT gamma-ray signal from Earth Limb, systematic detector effects and their implications for the 130 GeV gamma-ray excess
The European Physical Journal C, 2013Co-Authors: A Hektor, M Raidal, E TempelAbstract:We look for possible spectral features and systematic effects in the Fermi LAT publicly available high-energy gamma-ray data by studying photons from the Galactic center, nearby galaxy clusters, nearby brightest galaxies, AGNs, unassociated sources, hydrogen clouds and from the Earth Limb. Apart from the already known 130 GeV gamma-ray excesses from the first two sources, we find no statistically significant excesses from any of the cosmological sources nor from any control region. Therefore our main effort goes to the study of gamma rays appearing from the Earth Limb. In the energy range of 30 to 200 GeV the Earth Limb gamma-ray spectrum follows a power-law with spectral index 2.86±0.05 at 95 % CL, in a good agreement with the PAMELA measurement of the cosmic ray proton spectral index of 2.82–2.85, confirming the physical origin of the Limb gamma-rays. In subsets of the Earth Limb data at small photon incidence angle spectral features occur, including a feature at 130 GeV. We observe a systematic ∼2 σ -level difference in the Earth Limb spectra with small and large incidence angles. The behavior of those spectral features as well as the background indicates that those may be statistical fluctuations or complicated unknown systematic effects of the Fermi LAT. In the latter case, only the Fermi LAT Collaboration can give the final answer having access to raw data and all details of the reconstruction.
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fermi lat gamma ray signal from Earth Limb systematic detector effects and their implications for the 130 gev gamma ray excess
arXiv: High Energy Astrophysical Phenomena, 2012Co-Authors: A Hektor, M Raidal, E TempelAbstract:We look for possible spectral features and systematic effects in Fermi-LAT publicly available high-energy gamma-ray data by studying photons from the Galactic centre, nearby galaxy clusters, nearby brightest galaxies, AGNs, unassociated sources, hydrogen clouds and Earth Limb. Apart from already known 130 GeV gamma-ray excesses from the first two sources, we find no new statistically significant signal from others. Much of our effort goes to studying Earth Limb photons. In the energy range 30 GeV to 200 GeV the Earth Limb gamma-ray spectrum follows power-law with spectral index 2.87\pm 0.04 at 95 % CL, in a good agreement with the PAMELA measurement of cosmic ray proton spectral index between 2.82-2.85, confirming the physical origin of the Limb gamma-rays. In small subsets of Earth Limb data with small photon incidence angle it is possible to obtain spectral features at different energies, including at 130 GeV, but determination of background, thus their significances, has large uncertainties in those cases. We observe systematic 2\sigma level differences in the Earth Limb spectra of gamma-rays with small and large incidence angles. The behaviour of those spectral features as well as background indicates that they are likely statistical fluctuations.
Christopher J Mertens - One of the best experts on this subject based on the ideXlab platform.
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retrieval of kinetic temperature and carbon dioxide abundance from non local thermodynamic equilibrium Limb emission measurements made by the saber experiment on the timed satellite
Remote Sensing of Clouds and the Atmosphere VII, 2003Co-Authors: Christopher J Mertens, Martin G Mlynczak, M Lopezpuertas, Peter P Wintersteiner, Richard H Picard, Jeremy R Winick, Larry L Gordley, James M RussellAbstract:The Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) experiment was launched onboard the TIMED satellite in December, 2001. SABER is designed to provide measurements of temperature, constituents, and the key radiative and chemical sources and sinks of energy in the mesosphere and lower thermosphere (MLT). SABER measures Earth Limb emission in 10 broadband radiometer channels ranging from 1.27 μm to 17 μm. Measurements are made both day and night over the latitude range from 52°S to 83°N with alternating hemisphere coverage every 60 days. In this paper we concentrate on retrieved profiles of kinetic temperature (Tk) and CO2 volume mixing ratio (vmr), inferred from observed 15 μm and 4.3 μm Limb emissions. SABER-measured Limb radiances are in non-local thermodynamic equilibrium (non-LTE) in the MLT region. The complexity of non-LTE radiation transfer combined with the large volume of data measured by SABER requires new retrieval approaches and radiative transfer techniques to accurately and efficiently retrieve the data products. In this paper we present the salient features of the coupled non-LTE Tk/CO2 retrieval algorithm, along with preliminary results.
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impact of non lte processes on middle atmospheric water vapor retrievals from simulated measurements of 6 8 μm Earth Limb emission
Geophysical Research Letters, 2002Co-Authors: Christopher J Mertens, Martin G Mlynczak, M Lopezpuertas, Ellis E RemsbergAbstract:[1] We present an efficient and accurate algorithm for the retrieval of water vapor (H2O) volume mixing ratio (vmr) in the middle atmosphere from satellite measurements of 6.8 μm Earth Limb emission, which rigorously includes non-local thermodynamic equilibrium (non-LTE) processes. A number of retrieval studies have been conducted with this algorithm leading to three major conclusions about the retrieval of H2O in the middle atmosphere: (1) satellite measurements of 6.3 μm Limb emission must be made to high altitudes (85–90 km), where the few optically thick H2O absorption lines become optically thin, in order to prevent large errors in retrieved stratospheric and mesospheric H2O vmr; (2) the impact of non-LTE on nighttime H2O retrievals is greater than previously thought; (3) the enhancements in the daytime H2O channel radiances of the NIMBUS 7 LIMS experiment may be entirely due to non-LTE emission from the H2O 6.3 μm bands.
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retrieval of mesospheric and lower thermospheric kinetic temperature from measurements of co2 15 µm Earth Limb emission under non lte conditions
Geophysical Research Letters, 2001Co-Authors: Christopher J Mertens, Martin G Mlynczak, M Lopezpuertas, Peter P Wintersteiner, Richard H Picard, Jeremy R Winick, Larry L Gordley, James M RussellAbstract:We present a new algorithm for the retrieval of kinetic temperature in the terrestrial mesosphere and lower thermosphere from measurements of CO2 15 µm Earth Limb emission. Non-local-thermodynamic-equilibrium (non-LTE) processes are rigorously included in the new algorithm, necessitated by the prospect of satellite-based Limb radiance measurements to be made from the TIMED/SABER platform in the near future between 15 km and 120 km tangent altitude. The algorithm requires 20 seconds to retrieve temperature to better than 3 K accuracy on a desktop computer, easily enabling its use in operational processing of satellite data. We conclude this letter with a study of the sensitivity of the retrieved temperatures to parameters used in the non-LTE models, including sensitivity to the rate constant for physical quenching of CO2 bending mode vibrations by atomic oxygen.
James M Russell - One of the best experts on this subject based on the ideXlab platform.
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retrieval of kinetic temperature and carbon dioxide abundance from non local thermodynamic equilibrium Limb emission measurements made by the saber experiment on the timed satellite
Remote Sensing of Clouds and the Atmosphere VII, 2003Co-Authors: Christopher J Mertens, Martin G Mlynczak, M Lopezpuertas, Peter P Wintersteiner, Richard H Picard, Jeremy R Winick, Larry L Gordley, James M RussellAbstract:The Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) experiment was launched onboard the TIMED satellite in December, 2001. SABER is designed to provide measurements of temperature, constituents, and the key radiative and chemical sources and sinks of energy in the mesosphere and lower thermosphere (MLT). SABER measures Earth Limb emission in 10 broadband radiometer channels ranging from 1.27 μm to 17 μm. Measurements are made both day and night over the latitude range from 52°S to 83°N with alternating hemisphere coverage every 60 days. In this paper we concentrate on retrieved profiles of kinetic temperature (Tk) and CO2 volume mixing ratio (vmr), inferred from observed 15 μm and 4.3 μm Limb emissions. SABER-measured Limb radiances are in non-local thermodynamic equilibrium (non-LTE) in the MLT region. The complexity of non-LTE radiation transfer combined with the large volume of data measured by SABER requires new retrieval approaches and radiative transfer techniques to accurately and efficiently retrieve the data products. In this paper we present the salient features of the coupled non-LTE Tk/CO2 retrieval algorithm, along with preliminary results.
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retrieval of mesospheric and lower thermospheric kinetic temperature from measurements of co2 15 µm Earth Limb emission under non lte conditions
Geophysical Research Letters, 2001Co-Authors: Christopher J Mertens, Martin G Mlynczak, M Lopezpuertas, Peter P Wintersteiner, Richard H Picard, Jeremy R Winick, Larry L Gordley, James M RussellAbstract:We present a new algorithm for the retrieval of kinetic temperature in the terrestrial mesosphere and lower thermosphere from measurements of CO2 15 µm Earth Limb emission. Non-local-thermodynamic-equilibrium (non-LTE) processes are rigorously included in the new algorithm, necessitated by the prospect of satellite-based Limb radiance measurements to be made from the TIMED/SABER platform in the near future between 15 km and 120 km tangent altitude. The algorithm requires 20 seconds to retrieve temperature to better than 3 K accuracy on a desktop computer, easily enabling its use in operational processing of satellite data. We conclude this letter with a study of the sensitivity of the retrieved temperatures to parameters used in the non-LTE models, including sensitivity to the rate constant for physical quenching of CO2 bending mode vibrations by atomic oxygen.
