Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 1996
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1996adil...as...01s&link_type=abstract
NCSA Astronomy Digital Image Library
Astronomy and Astrophysics
Astronomy
Scientific paper
We present the first high-spatial-resolution images of a solar flare at millimeter wavelengths. On 1994 August 17, a GOES soft X--ray class M1 flare was observed by the Berkeley--Illinois--Maryland Array (BIMA) at 86 GHz, by the Nobeyama 17 GHz array, and by the Yohkoh spacecraft. The flare displayed both a prominent impulsive phase in microwaves and a gradual phase which lasted over 30 minutes. The millimeter data were taken only during the gradual phase. The millimeter images show a source with a size of $\sim$8\arcsec, a peak brightness temperature of ~ 10^6 K, and maximum optical depth of 0.09. At both X--ray and radio wavelengths the emitting region appeared to be compact (< 20 arcseconds). In soft X--ray the images are resolved into two sources: one located at a footpoint and the other at the top of the flaring loop. The millimeter emission is consistent with the predicted free-free flux from an isothermal temperature (~ 14 MK) looptop source and a multi--temperature footpoint source with a hot (~ 22 MK) and a cold (~ 12 MK) component. Most (80%) of the millimeter flux density originates from the top of the magnetic loop, and the footpoint contribution is only 20%.
de Pater Imke
Hudson Hugh S.
Kundu Mukul R.
Lin Robert P.
Shibasaku K.
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