The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
T R Jaffe - One of the best experts on this subject based on the ideXlab platform.
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the interstellar cosmic ray electron spectrum from Synchrotron radiation and direct measurements
Astronomy and Astrophysics, 2011Co-Authors: A W Strong, E Orlando, T R JaffeAbstract:Aims. We exploit Synchrotron radiation to constrain the low-energy interstellar electron spectrum, using various radio surveys and connecting with electron data from Fermi-LAT and other experiments. Methods. The GALPROP programme for cosmic-ray propagation, gamma-ray and Synchrotron radiation is used. Secondary electrons and positrons are included. Propagation models based on cosmic-ray and gamma-ray data are tested against Synchrotron data from 22 MHz to 94 GHz. Results. The Synchrotron data confirm the need for a low-energy break in the cosmic-ray electron injection spectrum. The interstellar spectrum below a few GeV has to be lower than standard models predict, and this suggests less solar modulation than usually assumed. Reacceleration models are more difficult to reconcile with the Synchrotron constraints. We show that secondary leptons are important for the interpretation of Synchrotron emission. We also consider a cosmic-ray propagation origin for the low-energy break. Conclusions. Exploiting the complementary information on cosmic rays and Synchrotron gives unique and essential constraints on electrons, and has implications for gamma rays. This connection is especially relevant now in view of the ongoing Planck and Fermi missions.
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the interstellar cosmic ray electron spectrum from Synchrotron radiation and direct measurements
arXiv: High Energy Astrophysical Phenomena, 2011Co-Authors: A W Strong, E Orlando, T R JaffeAbstract:Context: The relation between Galactic cosmic-ray electrons, magnetic fields and Synchrotron radiation. Aims: We exploit Synchrotron radiation to constrain the low-energy interstellar electron spectrum, using various radio surveys and connecting with electron data from Fermi-LAT and other experiments. Methods: The GALPROP programme for cosmic-ray propagation, gamma-ray and Synchrotron radiation is used. Secondary electrons and positrons are included. Propagation models based on cosmic-ray and gamma-ray data are tested against Synchrotron data from 22 MHz to 94 GHz. Results: The Synchrotron data confirm the need for a low-energy break in the cosmic-ray electron injection spectrum. The interstellar spectrum below a few GeV has to be lower than standard models predict, and this suggests less solar modulation than usually assumed. Reacceleration models are more difficult to reconcile with the Synchrotron constraints. We show that secondary leptons are important for the interpretation of Synchrotron emission. We also consider a cosmic-ray propagation origin for the low-energy break. Conclusions: Exploiting the complementary information on cosmic rays and Synchrotron gives unique and essential constraints on electrons, and has implications for gamma rays. This connection is especially relevant now in view of the ongoing PLANCK and Fermi missions.
A W Strong - One of the best experts on this subject based on the ideXlab platform.
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the interstellar cosmic ray electron spectrum from Synchrotron radiation and direct measurements
Astronomy and Astrophysics, 2011Co-Authors: A W Strong, E Orlando, T R JaffeAbstract:Aims. We exploit Synchrotron radiation to constrain the low-energy interstellar electron spectrum, using various radio surveys and connecting with electron data from Fermi-LAT and other experiments. Methods. The GALPROP programme for cosmic-ray propagation, gamma-ray and Synchrotron radiation is used. Secondary electrons and positrons are included. Propagation models based on cosmic-ray and gamma-ray data are tested against Synchrotron data from 22 MHz to 94 GHz. Results. The Synchrotron data confirm the need for a low-energy break in the cosmic-ray electron injection spectrum. The interstellar spectrum below a few GeV has to be lower than standard models predict, and this suggests less solar modulation than usually assumed. Reacceleration models are more difficult to reconcile with the Synchrotron constraints. We show that secondary leptons are important for the interpretation of Synchrotron emission. We also consider a cosmic-ray propagation origin for the low-energy break. Conclusions. Exploiting the complementary information on cosmic rays and Synchrotron gives unique and essential constraints on electrons, and has implications for gamma rays. This connection is especially relevant now in view of the ongoing Planck and Fermi missions.
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the interstellar cosmic ray electron spectrum from Synchrotron radiation and direct measurements
arXiv: High Energy Astrophysical Phenomena, 2011Co-Authors: A W Strong, E Orlando, T R JaffeAbstract:Context: The relation between Galactic cosmic-ray electrons, magnetic fields and Synchrotron radiation. Aims: We exploit Synchrotron radiation to constrain the low-energy interstellar electron spectrum, using various radio surveys and connecting with electron data from Fermi-LAT and other experiments. Methods: The GALPROP programme for cosmic-ray propagation, gamma-ray and Synchrotron radiation is used. Secondary electrons and positrons are included. Propagation models based on cosmic-ray and gamma-ray data are tested against Synchrotron data from 22 MHz to 94 GHz. Results: The Synchrotron data confirm the need for a low-energy break in the cosmic-ray electron injection spectrum. The interstellar spectrum below a few GeV has to be lower than standard models predict, and this suggests less solar modulation than usually assumed. Reacceleration models are more difficult to reconcile with the Synchrotron constraints. We show that secondary leptons are important for the interpretation of Synchrotron emission. We also consider a cosmic-ray propagation origin for the low-energy break. Conclusions: Exploiting the complementary information on cosmic rays and Synchrotron gives unique and essential constraints on electrons, and has implications for gamma rays. This connection is especially relevant now in view of the ongoing PLANCK and Fermi missions.
Eli Waxman - One of the best experts on this subject based on the ideXlab platform.
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gamma ray burst afterglow polarization and analytic light curves
The Astrophysical Journal, 1999Co-Authors: Andrei Gruzinov, Eli WaxmanAbstract:Gamma-ray burst afterglow polarization is discussed. We find an observable, up to ~10%, polarization, if the magnetic field coherence length grows at about the speed of light after the field is generated at the shock front. Detection of a polarized afterglow would show that collisionless ultrarelativistic shocks can generate strong large-scale magnetic fields and confirm the Synchrotron afterglow model. Nondetection, at the ~1% level, would imply that either the Synchrotron emission model is incorrect or that strong magnetic fields, after they are generated in the shock, somehow manage to stay undissipated at "microscopic," skin depth, scales. Analytic light curves of Synchrotron emission from an ultrarelativistic self-similar blast wave are obtained for an arbitrary electron distribution function, taking into account the effects of Synchrotron cooling. The peak Synchrotron flux and the flux at frequencies much smaller than the peak frequency are insensitive to the details of the electron distribution function; hence, their observational determination would provide strong constraints on blast-wave parameters.
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gamma ray burst afterglow polarization and analytic light curves
arXiv: Astrophysics, 1998Co-Authors: Andrei Gruzinov, Eli WaxmanAbstract:GRB afterglow polarization is discussed. We find an observable, up to 10%, polarization, if the magnetic field coherence length grows at about the speed of light after the field is generated at the shock front. Detection of a polarized afterglow would show that collisionless ultrarelativistic shocks can generate strong large scale magnetic fields and confirm the Synchrotron afterglow model. Non-detection, at a 1% level, would imply that either the Synchrotron emission model is incorrect, or that strong magnetic fields, after they are generated in the shock, somehow manage to stay un-dissipated at ``microscopic'', skin depth, scales. Analytic lightcurves of Synchrotron emission from an ultrarelativistic self-similar blast wave are obtained for an arbitrary electron distribution function, taking into account the effects of Synchrotron cooling. The peak Synchrotron flux and the flux at frequencies much smaller than the peak frequency are insensitive to the details of the electron distribution function; hence their observational determination would provide strong constraints on blast wave parameters.
Franz Pfeiffer - One of the best experts on this subject based on the ideXlab platform.
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x ray phase contrast tomography with a compact laser driven Synchrotron source
Proceedings of the National Academy of Sciences of the United States of America, 2015Co-Authors: Elena Eggl, Simone Schleede, Martin Bech, Klaus Achterhold, R J Loewen, R D Ruth, Franz PfeifferAbstract:Between X-ray tubes and large-scale Synchrotron sources, a large gap in performance exists with respect to the monochromaticity and brilliance of the X-ray beam. However, due to their size and cost, large-scale Synchrotrons are not available for more routine applications in small and medium-sized academic or industrial laboratories. This gap could be closed by laser-driven compact Synchrotron light sources (CLS), which use an infrared (IR) laser cavity in combination with a small electron storage ring. Hard X-rays are produced through the process of inverse Compton scattering upon the intersection of the electron bunch with the focused laser beam. The produced X-ray beam is intrinsically monochromatic and highly collimated. This makes a CLS well-suited for applications of more advanced––and more challenging––X-ray imaging approaches, such as X-ray multimodal tomography. Here we present, to our knowledge, the first results of a first successful demonstration experiment in which a monochromatic X-ray beam from a CLS was used for multimodal, i.e., phase-, dark-field, and attenuation-contrast, X-ray tomography. We show results from a fluid phantom with different liquids and a biomedical application example in the form of a multimodal CT scan of a small animal (mouse, ex vivo). The results highlight particularly that quantitative multimodal CT has become feasible with laser-driven CLS, and that the results outperform more conventional approaches.
Martin Bech - One of the best experts on this subject based on the ideXlab platform.
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x ray phase contrast tomography with a compact laser driven Synchrotron source
Proceedings of the National Academy of Sciences of the United States of America, 2015Co-Authors: Elena Eggl, Simone Schleede, Martin Bech, Klaus Achterhold, R J Loewen, R D Ruth, Franz PfeifferAbstract:Between X-ray tubes and large-scale Synchrotron sources, a large gap in performance exists with respect to the monochromaticity and brilliance of the X-ray beam. However, due to their size and cost, large-scale Synchrotrons are not available for more routine applications in small and medium-sized academic or industrial laboratories. This gap could be closed by laser-driven compact Synchrotron light sources (CLS), which use an infrared (IR) laser cavity in combination with a small electron storage ring. Hard X-rays are produced through the process of inverse Compton scattering upon the intersection of the electron bunch with the focused laser beam. The produced X-ray beam is intrinsically monochromatic and highly collimated. This makes a CLS well-suited for applications of more advanced––and more challenging––X-ray imaging approaches, such as X-ray multimodal tomography. Here we present, to our knowledge, the first results of a first successful demonstration experiment in which a monochromatic X-ray beam from a CLS was used for multimodal, i.e., phase-, dark-field, and attenuation-contrast, X-ray tomography. We show results from a fluid phantom with different liquids and a biomedical application example in the form of a multimodal CT scan of a small animal (mouse, ex vivo). The results highlight particularly that quantitative multimodal CT has become feasible with laser-driven CLS, and that the results outperform more conventional approaches.
