TEMPORAL AND SPATIAL ANALYSES OF SPECTRAL INDICES OF NONTHERMAL EMISSIONS DERIVED FROM HARD X-RAYS AND MICROWAVES

Journal Article · Fri Feb 15 04:00:00 EST 2013 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/763/2/87· OSTI ID:22167159

Asai, Ayumi ^[1]; Kiyohara, Junko; Takasaki, Hiroyuki ^[2]; Narukage, Noriyuki ^[3]; Yokoyama, Takaaki ^[4]; Masuda, Satoshi ^[5]; Shimojo, Masumi ^[6]; Nakajima, Hiroshi ^[7]

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1. Unit of Synergetic Studies for Space, Kyoto University, Yamashina, Kyoto, 607-8471 (Japan)
2. Kwasan and Hida Observatories, Kyoto University, Yamashina, Kyoto, 607-8471 (Japan)
3. Institute of Space and Astronomical Science, Japan Aerospace Exploration Agency, Chuo, Sagamihara, Kanagawa, 229-8510 (Japan)
4. Department of Earth and Planetary Science, University of Tokyo, Hongo, Bunkyo, Tokyo, 113-0033 (Japan)
5. Solar-Terrestrial Environment Laboratory, Nagoya University, Chikusa, Nagoya, Aichi, 464-8601 (Japan)
6. National Astronomical Observatory of Japan, Mitaka, Tokyo, 181-8588 (Japan)
7. Nobeyama Solar Radio Observatory, National Astronomical Observatory of Japan, Minamimaki, Minamisaku, Nagano, 384-1305 (Japan)

We studied electron spectral indices of nonthermal emissions seen in hard X-rays (HXRs) and microwaves. We analyzed 12 flares observed by the Hard X-Ray Telescope aboard Yohkoh, Nobeyama Radio Polarimeters, and the Nobeyama Radioheliograph (NoRH), and compared the spectral indices derived from total fluxes of HXRs 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 HXRs {delta} {sub X} and those from microwaves {delta}{sub {mu}} ({Delta}{delta} = {delta} {sub X} - {delta}{sub {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} {sub X} evolve synchronously with those of the microwave spectral index {delta}{sub {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}{sub {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.

• OSTI ID: 22167159
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 763; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
COMPARATIVE EVALUATIONS
ELECTRON SPECTRA
EMISSION
GAMMA RADIATION
HARD X RADIATION
KEV RANGE
MAGNETIC FIELDS
MICROWAVE RADIATION
SUN
TELESCOPES