Temporal and Spatial Analyses of Spectral Indices of Nonthermal Emissions Derived from Hard X-Rays and Microwaves
| Autor: | Hiroyuki Takasaki, Satoshi Masuda, Noriyuki Narukage, Hiroshi Nakajima, Ayumi Asai, Junko Kiyohara, Takaaki Yokoyama, Masumi Shimojo |
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| Jazyk: | angličtina |
| Rok vydání: | 2012 |
| Předmět: |
Physics
Sun: flares Spectral index Sun: radio radiation Sun: corona Astrophysics::High Energy Astrophysical Phenomena FOS: Physical sciences Astronomy and Astrophysics Astrophysics Electron Astrophysics::Cosmology and Extragalactic Astrophysics Sun: X-rays gamma rays Spectral line law.invention Magnetic field Telescope Distribution (mathematics) Astrophysics - Solar and Stellar Astrophysics Space and Planetary Science law Astrophysics::Solar and Stellar Astrophysics Microwave Energy (signal processing) Solar and Stellar Astrophysics (astro-ph.SR) acceleration of particles |
| Popis: | We studied electron spectral indices of nonthermal emissions seen in hard X-rays (HXRs) and in microwaves. We analyzed 12 flares observed by the Hard X-ray Telescope aboard {\it Yohkoh}, Nobeyama Radio Polarimeters (NoRP), and the Nobeyama Radioheliograph (NoRH), and compared the spectral indices derived from total fluxes of hard X-rays and microwaves. Except for four events, which have very soft HXR spectra suffering from the thermal component, these flares show a gap $\Delta\delta$ between the electron spectral indices derived from hard X-rays $\delta_{X}$ and those from microwaves $\delta_{\mu}$ ($\Delta\delta = \delta_{X} - \delta_{\mu}$) of about 1.6. Furthermore, from the start to the peak times of the HXR bursts, the time profiles of the HXR spectral index $\delta_{X}$ evolve synchronously with those of the microwave spectral index $\delta_{\mu}$, keeping the constant gap. We also examined the spatially resolved distribution of the microwave spectral index by using NoRH data. The microwave spectral index $\delta_{\mu}$ tends to be larger, which means a softer spectrum, at HXR footpoint sources with stronger magnetic field than that at the loop tops. These results suggest that the electron spectra are bent at around several hundreds of keV, and become harder at the higher energy range that contributes the microwave gyrosynchrotron emission. Comment: 24 pages, 6 figures, accepted for publication in ApJ |
| Databáze: | OpenAIRE |
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