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Astronomy Letters - The emission from the Crab nebula exhibits a significant gamma-ray variability. In this paper we have analyzed this variability in terms of periodicity. Using the pulsar... 相似文献
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V. V. Grechnev V. I. Kiselev L. K. Kashapova A. A. Kochanov I. V. Zimovets A. M. Uralov B. A. Nizamov I. Y. Grigorieva D. V. Golovin M. L. Litvak I. G. Mitrofanov A. B. Sanin 《Solar physics》2018,293(10):133
The far-side solar eruptive event SOL2014-09-01 produced hard electromagnetic and radio emissions that were observed with detectors at near-Earth vantage points. Especially challenging was a long-duration >?100 MeV \(\gamma\)-ray burst that was probably produced by accelerated protons exceeding 300 MeV. This observation raised the question how high-energy protons could reach the Earth-facing solar surface. Some preceding studies discussed a scenario in which protons accelerated by a shock driven by a coronal mass ejection high in the corona return to the solar surface. We continue with the analysis of this challenging event, involving radio images from the Nançay Radioheliograph and hard X-ray data from the High Energy Neutron Detector (HEND) of the Gamma-Ray Spectrometer onboard the Mars Odyssey space observatory located near Mars. HEND recorded unocculted flare emission. The results indicate that the emissions observed from the Earth’s direction were generated by flare-accelerated electrons and protons trapped in static long coronal loops. They can be reaccelerated in these loops by a shock wave that was excited by the eruption, being initially not driven by a coronal mass ejection. The results highlight ways to address the remaining questions. 相似文献
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The influence of various chemical elements on radiative cooling of the gas flowing from a viscous jump is investigated in a model with a stationary shock in the atmosphere of a cool star. A closed system of equations is written for the thermal energy per heavy particle, the electron temperature, and the relative concentrations of elements in all ionization states. In addition to hydrogen and helium, atomic, singly ionized, and doubly ionized carbon, nitrogen, oxygen, sodium, magnesium, aluminum, silicon, sulfur, potassium, calcium, and iron are included, assuming they have their normal cosmic abundances. The high optical depth in Lyman-series lines leads to a return of the thermal energy to electrons via secondary collisions. As a result, the contribution of hydrogen to the cooling rate falls to the level of the contribution of metals, mainly carbon, magnesium, and iron. Thus, such shock models are able to explain the presence of bright metal lines in the spectra of cool and solar-type stars. 相似文献
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Geomagnetism and Aeronomy - We analyze physical characteristics of late-type stars wherein the Kepler mission registered superflares. We use the revised stellar fundamental parameters, i.e.... 相似文献
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M. A. Livshits I. V. Zimovets D. V. Golovin B. A. Nizamov V. I. Vybornov I. G. Mitrofanov A. S. Kozyrev M. L. Litvak A. B. Sanin V. I. Tretyakov 《Astronomy Reports》2017,61(9):791-804
The study of nonstationary processes in the Sun is of great interest, and multi-wavelength observations and the registration of magnetic fields have been carried out using both ground-based telescopes and several specialized spacecraft in near-Earth orbits in recent years. However, the acquisition of new, reliable information on their hard X-ray radiation remains necessary, in particular, if the corresponding spacecraft provide additional information, e.g., in regard to flare observations from directions other than the Sun–Earth direction. This paper presents a catalog of powerful solar flares registered by the High Energy Neutron Detector (HEND) designed at the Space Research Institute of the Russian Academy of Sciences. HEND is mounted onboard the 2001Mars Odyssey spacecraft. It operated successfully during the flight to Mars and is currently operating in near-Mars orbit. Apart from neutrons, HEND is sensitive to hard X-ray (up to 300 keV) and gamma-ray radiation (above 300 keV). This radiation is registered by two scintillators: an outer one that is sensitive to photons above 40 keV and an inner one sensitive to photons above 200 keV. The catalog was created using a new procedure for calibration of the data. For the most powerful 60 solar flares in the visible and far sides of the Sun (for a terrestrial observer), time profiles of the flare radiation summed over all channels of the X-ray, and in some cases the gamma-ray, bands are provided, as well as spectra and characteristics of power-law fits. The results of previous studies of the Sun using HEND and the potential for further use of these data are discussed. 相似文献
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