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Temporal and Spatial Analyses of Spectral Indices of Nonthermal Emissions Derived from Hard X-Rays and Microwaves  

Ayumi Asai   Submitted: 2012-12-10 18:28

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 Deltadelta between the electron spectral indices derived from hard X-rays deltaX and those from microwaves deltamu (Deltadelta = deltaX - deltamu) of about 1.6. Furthermore, from the start to the peak times of the HXR bursts, the time profiles of the HXR spectral index deltaX evolve synchronously with those of the microwave spectral index deltamu, keeping the constant gap. We also examined the spatially resolved distribution of the microwave spectral index by using NoRH data. The microwave spectral index deltamu 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.

Authors: Ayumi Asai, Junko Kiyohara, Hiroyuki Takasaki, Noriyuki Narukage, Takaaki Yokoyama, Satoshi Masuda, Masumi Shimojo, and Hiroshi Nakajima
Projects: Nobeyama Radioheliograph,Yohkoh-HXT,Yohkoh-WBS

Publication Status: ApJ (accepted)
Last Modified: 2012-12-10 18:39
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First Simultaneous Observation of Hα Moreton Wave, EUV Wave, and Filament/Prominence Oscillations  

Ayumi Asai   Submitted: 2011-12-27 00:40

This abstract was corrupted following database problems and is being recovered. It will be restored as quickly as possible. Any questions, please send them to Alisdair. Sorry for any incovenience.


Authors: Asai, A., Ishii, T.T., Kitai R., Ichimoto, K., UeNo, S., Nagata, S., Morita, S., Nishida, K., Shiota, D., Oi, A., Akioka, M., Shibata, K.
Projects: SDO-AIA,STEREO

Publication Status: accepted by ApJL
Last Modified: 2011-12-28 12:07
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A Study on Red Asymmetry of Hα Flare Ribbons Using Narrowband Filtergram in the 2001 April 10 Solar Flare  

Ayumi Asai   Submitted: 2011-10-03 10:58

This abstract was corrupted following database problems and is being recovered. It will be restored as quickly as possible. Any questions, please send them to Alisdair. Sorry for any incovenience.


Authors: Asai, A., Ichimoto, K., Kitai, R., Kurokawa, H., and Shibata, K.
Projects: None

Publication Status: accepted by PASJ, (publication in April 2012, V64 No2 issue)
Last Modified: 2011-10-03 11:11
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Imaging Spectroscopy on Preflare Coronal Nonthermal Sources Associated with the 2002 July 23 Flare  

Ayumi Asai   Submitted: 2009-01-22 19:24

We present a detailed examination on the coronal nonthermal emissions during the preflare phase of the X4.8 flare that occurred on 2002 July 23. The microwave (17 GHz and 34 GHz) data obtained with Nobeyama Radioheliograph, at Nobeyama Solar Radio Observatory and the hard X-ray (HXR) data taken with {it Reuven Ramaty High Energy Solar Spectroscopic Imager} obviously showed nonthermal sources that are located above the flare loops during the preflare phase. We performed imaging spectroscopic analyses on the nonthermal emission sources both in microwaves and in HXRs, and confirmed that electrons are accelerated from several tens of keV to more than 1~MeV even in this phase. If we assume the thin-target model for the HXR emission source, the derived electron spectral indices (sim 4.7) is the same value as that from microwaves (sim 4.7) within the observational uncertainties, which implies that the distribution of the accelerated electrons follows a single power-law. The number density of the microwave-emitting electrons is, however, larger than that of the HXR-emitting electrons, unless we assume low ambient plasma density of about 1.0 imes 109~cm-3 for the HXR-emitting region. If we adopt the thick-target model for the HXR emission source, on the other hand, the electron spectral index (sim 6.7) is much different, while the gap of the number density of the accelerated electrons is somewhat reduced.

Authors: Ayumi Asai, Hiroshi Nakajima, Masumi Shimojo, Takaaki Yokoyama, Satoshi Masuda, Säm Krucker
Projects: RHESSI

Publication Status: ApJ (accepted)
Last Modified: 2009-01-23 09:36
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Evolution of Anemone AR NOAA 10798 and the Related Geo-Effective Flares and CMEs  

Ayumi Asai   Submitted: 2008-12-14 20:54

We present a detailed examination of the features of the Active Region (AR) NOAA 10798. This AR generated coronal mass ejections (CMEs) that caused a large geomagnetic storm on 24 August 2005 with the minimum Dst index of -216 nT. We examined the evolution of the AR and the features on/near the solar surface and in the interplanetary space. The AR emerged in the middle of a small coronal hole, and formed a {it sea anemone} like configuration. Hα filaments were formed in the AR, which have southward axial field. Three M-class flares were generated, and the first two that occurred on 22 August 2005 were followed by Halo-type CMEs. The speeds of the CMEs were fast, and recorded about 1200 and 2400 km s-1, respectively. The second CME was especially fast, and caught up and interacted with the first (slower) CME during their travelings toward Earth. These acted synergically to generate an interplanetary disturbance with strong southward magnetic field of about -50 nT, which was followed by the large geomagnetic storm.

Authors: Ayumi Asai, Kazunari Shibata, Takako T. Ishii, Mitsuo Oka, Ryuho Kataoka, Ken'ichi Fujiki, Nat Gopalswamy
Projects: None

Publication Status: JGR (accepted)
Last Modified: 2008-12-15 10:11
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Subject will be restored when possible  

Ayumi Asai   Submitted: 2008-06-05 23:36

We present a detailed examination of strongly blueshifted emission lines observed with the EUV Imaging Spectrometer on board the Hinode satellite. We found two kinds of blueshifted phenomenon associated with the X3.4 flare that occurred on 2006 December 13. One was related to a plasmoid ejection seen in soft X-rays. It was very bright in all the lines used for the observations. The other was associated with the faint arc-shaped ejection seen in soft X-rays. The soft X-ray ejection is thought to be an MHD fast-mode shock wave. This is therefore the first spectroscopic observation of an MHD fast-mode shock wave associated with a flare.

Authors: Ayumi Asai, Hirohisa Hara, Tetsuya Watanabe, Shinsuke Imada, Taro Sakao, Noriyuki Narukage, J. L. Culhane, G. A. Doschek
Projects: Hinode/EIS

Publication Status: ApJ (accepted; 2008, 684, in press)
Last Modified: 2008-09-23 21:00
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Abstracts by Author
Temporal and Spatial Analyses of Spectral Indices of Nonthermal Emissions Derived from Hard X-Rays and Microwaves
First Simultaneous Observation of H-alpha Moreton Wave, EUV Wave, and Filament/Prominence Oscillations
A Study on Red Asymmetry of H-alpha Flare Ribbons Using Narrowband Filtergram in the 2001 April 10 Solar Flare
Imaging Spectroscopy on Preflare Coronal Nonthermal Sources Associated with the 2002 July 23 Flare
Evolution of Anemone AR NOAA 10798 and the Related Geo-Effective Flares and CMEs
Subject will be restored when possible

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