fl223.alissandrakis02 Posted: 17-Jan-96 Updated: 09-Aug-96 Events specified: N/A
C.E. Alissandrakis, F. Chiuderi Drago, Robert Bentley......(may be others)
This study follows that of the Active Region where the flares took place, which has been the subject of a previous proposal ( Alissandrakis, Chiuderi Drago, Shibasaki) and which will be submitted for publication very soon.
The purpose of this work is to analyze a number of flares observed with the Westerbork Synthesis Radio Telescope (WSRT) on July 3 and 4, 1993. All the flares were observed by SXT and three of them also by HXT, WBS and BCS. Such an ensemble of high performaning instruments was very seldom used in the past to study any coronal feature. It is very well known in fact that the comparison of the microwave emission with soft and hard x-ray observations can provide a unique diagnostic of the parameters existing in the flaring site.
The scheme of the present work can be summarized as follows: a) to check the radio burst position with respect to the SXT and HXT images and with the underlying magnetic field. b) to compare the impulsive phase of the radio burst with the WBS spectra taken at different times after the burst maximum, studying the evolution of the relativistic particles distribution due to collision and radiation, thus deriving information on the local electron density and magnetic field. c) to compare the radio emission during the thermal phase of the radio burst with that computed using the temperature and emission measure derived from soft and hard x-ray observations. A disagreement may indicate a contribution of the gyro-resonance to the emission, again supplying information on the local magnetic field.
The work was begun last sepember and it will take at least six months from now to be completed.
Update 09-Aug-96
A review paper was presented at the CESRA meeting last June in France with the following abstract:
Coronal Structures from X-ray and microwaves observations
C.E. Alissandrakis, F. Chiuderi Drago, E. Franciosini(*), R. Bentley.
The flare of July 4,1993 at about 740 UT has been observed by all instruments onboard the Yohkoh Satellite and by the Westerbork Synthesis Radio Telescope (WSRT) at 5 GHz. The radio flux observed at IZMIRAN at 3 GHz has been also used in this research. (Courtesy of I.Chertok).
The time profile at both radiofrequencies remarkably coincides with that observed in the four HXT channels.
The comparison of SXT and HXT images with the WSRT one dimensional position of the flare and with the Kitt Peak magnetograms of the Active Region suggests that the radio emission comes from the top of two small loops connecting oppositepolarities.Thickness and projected length of the loops are derived from the above comparison.
The spectral trend of HXT and WBS data (observed up to 200 kev) is very well fitted by a power law with spectral index 3.5, from which the distribution of non thermal x-ray emitting electrons is derived, in the thick target approximation.
By solvig the diffusion equation, assuming a constant input of electrons in the loop top, taking into account the radiation and collision losses and identifing the x-ray producing electrons with those escaping in the loss cone, the energy distribution of electrons responible for the radio emission by synchrotron radiation, is derived as a funcion of ratio between the magnetic field at the top and at the feet of the loop. The comparison with the observed flux at the two mentioned radio frequencies, can provide this ratio as well as the value of the thermal density, which strongly affects the synchrotron radio emission at low frequ$
(*) Name added after the first submission of the proposal.