Observations of Radio Sources with Distinctive Propaties in a Loop-like Structure during a Long Duration Durst

fl068.nishio01
Posted:  03-Sep-92
Updated: 06-Apr-93, 26-Nov-93, 28-Aug-94
Events specified: Flare on 28-Jun-92 at 02:13 UT

Category: Flare Activity

Collaboration: M. Nishio, H. Nakajima, Y. Hanaoka, K. Shibasaki, T. Takano, S. Enome, Y. Irimajiri and radio heliograph team.

Primary science question being addressed:

Mechanism of evolutions of the burst sources.

        Is the emission mechanism of the radio sources placesed     
      at the top and the foot point in a loop thermal or non-thermal?
       
 Where is the trigger point of the radio burst?

   On June 28, 0213UT - 0600, a X1.1 class flare was observed by
   the Nobeyama Radioheliograph. This burst (=flare) occured
   at the east limb of the sun. During the burst,
   two radio sources are observed at the top and the foot point of
   a loop-like strucure. Former one had gradual time variations and
   low polarization degrees. On the other hand, latter one showd
   relatively impulsive time profiles and high left handed circular
   polarization degrees. At early stage of the burst, elongations of
   the shape of the latter source to the former source were observed.
   In the SXT images before onset of the flare, an arcade-like
   structure could be seen with a bright point at the top of the
   arcade-like structure.
   These propaties will tell us a senario about the flare evolutions,
   that is the evaporation of the thermal plasmas caused by bombing
   of the non-thermal electrons to the foot point of the loop.

    We will use SXT whole-Sun images ( and partial frame images),
    radio heliograph images, magnetograms and H-alpha images.
    The SXT-images are used to identify loop-like structures and
    thermal sources corresonding to radio sources.

Update 28-Aug-94

Our proposal fl068.nishio01 entitled "Observations of Radio Sources with Distinctive Propaties..." have finished up as a letter paper on PASJ (PASJ 46, L11-L15 (1994)). Abstract of this paper has been sent to TBB_ADM by email (see update of 26-Nov-93).

Update 26-Nov-93

I have submitted the paper to PASJ as a letter.

Radio Imaging Observations of the Evolution of Thermal and Nonthermal Sources during a Gradual Burst

Masanori Nishio et al.

With the Nobeyama Radioheliograph, the evolution of thermal and nonthermal radio sources was observed during a gradual radio burst. The thermal sources were located near the top of an arcade-like soft X-ray structure observed by the Yohkoh satellite. The nonthermal source was observed near foot points of the arcade-like structure. During the early phase of the burst, an elongated structure was observed connecting one of the thermal sources and the nonthermal source. The elongation started from the location of the nonthermal source and gradually progressed to the thermal source placed just radially above the nonthermal source with the velocity of about 170 km $s^{-1}$. These observations imply that the thermal source and the nonthermal source are connected by a single magnetic loop, and that the elongation of the source structure is an indication of chromospheric evaporation by radio imaging observations. The energetics of the thermal and nonthermal sources was analyzed using the radio and soft X-ray data. We suggest that a continuous supply of accelerated electrons for about 1000 seconds can maintain the hot plasma observed at the foot points of the loop.

Update 06-Apr-93

Radio Imaging Observations of Thermal and Nonthermal Radio Sources during a Long Duration Burst

M. Nishio, H. Nakajima, S. Enome, K. Shibasaki, T. Takano, Y. Hanaoka, C. Torii, H. Sekiguchi, T. Bushimata, S. Kawashima, N. Shinohara, Y. Irimajiri, Y. Choi, H. Koshiishi, T. Kosugi, Y. Shiomi, M. Sawa and K. Kai*

Nobeyama Radio Observatory, National Astronomical Observatory, Minamisaku, Nagano 384-13, Japan

* Passed away in March, 1991.

Abstract

On June 28, 1992. an M1.1 class flare was observed by the Nobeyama Radioheliograph. This flare showed a gradual radio intensity enhancement overlaid by small impulsive variations. Imaging observations revealed, with the Radioheliograph during the flare, three compact sources at the east limb of the sun. One of the source showed characteristics of nonthermal activities and other two sources indicated thermal features. The nonthermal activities took place at a foot point of a soft X-ray loop observed by the YOHKOH satellite and one of the thermal sources was located near the top of the same loop. At the decay phase of precursor, an elongated structure from the nonthermal source was observed, which was stretched to the thermal source placed radially just off the nonthermal source. These data imply that the thermal and the nonthermal sources appeared at the different place of same magnetic loop and the nonthermal activities was an origin of this flare. The SXT images of the YOHKOH satellite support this result.