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The Sun

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Solar radio bursts study with high spatial and temporal resolution
V.A. Alexeev, A.F. Dementyev, B.N. Lipatov, V.F. Melnikov, M.B. Nechaeva, S.D. Snegirev, Yu.V. Tikhomirov
Radiophysical Research Institute NIRFI, Nizhny-Novgorod, Russia Theoretical and experimental researches of the energy release fragmentation in solar ares need observations with high spatial 0.01 1 arcsec and temporal 1 ms resolution. An important role for these studies as well as for the theory of short lived radio bursts can play VLBI observations. They could allow: a to study the spatial and temporal development of the are fragmentation; b to determine the size and the brightness temperature of the `elementary' burst sources; c to learn how di erent micro fragments of a are relate each other in space and in time; are there any deterministic connections exist between them or not. From 1994 we carry out interferometric observations of spatially fragmented energy release processes on the Sun including the study of spike-like radio bursts. During this time the receivers and other equipment for VLBI observations at the frequencies 327, 610 and 1665 MHz have been developed and constructed in NIRFI. Several VLBI stations all over the Russia were supplied by this set of equipment. The equipment for the new two-element radio interferometer with the intermediate baseline length of 70 km at 327 MHz has been installed at RAS NIRFI Zimenki" and Staraya Pustyn". In 1998 this interferometer operated as a part of the Russian and international radio interferometry networks. The similar equipment for the frequency of 610 MHz is under development now. To study solar ares and coronal plasmas with di erent baseline orientations and lengths from hundreds to several thousands kilometers at frequencies 327 and 1665 MHz a number of VLBI experiments have been carried out during 1994-1998 see Table 1. Until now the preliminary processing of magnetic tapes with data is done with the correlator Block 2 JPL Caltech, Pasadena, USA. ing is carried out by NIRFI group. However, in near future our broughtinto operation. This correlator is now under tests, and it data on magnetic tapes with the millisecond time resolution. The following main observational results have been obtained: a High precision of relative position measurements with millisecond time resolution via measuring phase variations of the interferometric signal is realized in interferometric observations of solar radio bursts in October-November 1994 at RAS NIRFI "Staraya Pustyn". For most intense bursts the precision of position measurements in these experiments was 1-2 arc seconds. It is shown for the rst time that the positions of sources of neighboring peaks in the course of the multi component bursts are sometimes remarkably di erent from each other and this di erence can reach 15 arc sec for the peaks separated only by 100-500 milliseconds. This fact puts new limitations on the theory of are fragmentation. in the MARK-2 format The nal data processown correlator will be will allow us to process


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The Sun

b The analysis of data obtained in the VLBI experiment of February 28, 1995 VA01, 18 cm wavelength, Medvezhie Ozera - Puschino baseline has been done. Two solar spikelikeevents with duration less than 2 s showed well pronounced interferometric responses with the excess over noise of 3-5 times. It is shown that the apparent angular sizes of the relevant solar radio sources are less than 5 arc sec. c To study of inhomogeneities in the solar corona and to research its e ect on size of spike sources the data analysis of the VLBI observations were carried out in 1994-1997. The in uence of coronal inhomogeneities on the interferometric spectrum of signals from far space radio source at 18 and 92 cm wavelengths for wide region of elongation angles 3-150 degrees was studied. New data on the structure of small scale and large scale inhomogeneities have been derived. It was found that inhomogeneity sizes are more than 200000 km along solar wind and 1500 2000 km across it. Hence, the radio interferometric equipment performed by our group and radio interferometric observations carried out autonomously and in the frame of VLBI networks allowus to found out some new spatial and temporal characteristics of sources of solar spike-like radio bursts. Proposed method of investigation of solar system allowed us to get new data on the structure of solar coronal plasma. Table 1 Date Interval of observation Stations UT 27.10.94 06:24-07:30 Ussuriysk, Puschino 28.10.94 05:42-07:00 28.02.95 05:20-08:20 Puschino, Medvezhie Ozera 24.10.95 25.10.95 27.10.95 30.11.97 01.12.97 02.12.97 05:30-07:30 05:30-07:30 05:30-07:30 07:30-08:23 07:27-08:23 07:32-08:25 08:50-09:26 03.12.97 06:57-10:44 04.12.97 06:57-10:42 04.04.98 06:00-08:40 Puschino, Medvezhie Ozera Puschino, Staraya Pustyn, Ooty, GMRT, Noto Frequency MHz 327 1665 327 327 1665 327 1666 327 Results no interferometric response spike-likeevents are found no interferometric response data is in process data pro data pro data pro is in cess is in cess is in cess

Puschino, Medvezhie Ozera, Noto, Urumchi 03.08.98 02:30-04:20 Zimenki, Staraya Pustyn 05:40-07:40 21.08.98 08:10-11:45 Medvezhie Ozera, Puschino, Urumchi, Medichina, Hart RAO 31.10.98 06:25-08:25 Puschino, Evpatoria, Staraya Pustyn, Urumchi, Ooty

data is in process