Professor Arnold Benz
Swiss Federal Institute of Technology ETH
Institute of Astronomy
Radio Astronomy Group
CH - 8092 Zurich
Tel: 41 1 6324223
Fax: 41 1 6321205
Radiophysical Research Institute
Department of Applied Radiophysics
RU - 603600 Nizhny Novgorod
Moscow Power Engineering Institute
Special Research Bureau
RU - 111250 Moscow
Institute of Radio Astronomy
Department of Decametric Radio Astronomy
UA - 310002 Kharkiv
Consiglio Nazionale delle Ricerche
Istituto di Radioastronomia
IT - 40129 Bologna
Russian Institute of Space Device Engineering
Deep Space Tracking Network Department
RU - 111024 Moscow
P.N.Lebedev Physical Institute
Astro Space Center
RU - 117810 Moscow
Low frequency VLBI research for solar studies and as a precursor to Space VLBI with RadioAstron
It is proposed to join the scientific and technical potentials of research groups from Switzerland, Italy, Russia, Ukraine, India, USA and Sweden for equipping the radio telescopes of the former Soviet Union by standard receiving-recording hardware in the 327 MHz band in order to conduct a multifaceted research programme in interests of future Space VLBI RadioAstron mission and solar studies together with telescopes Noto, Ooty, GMRT, Shanghai, Urumqi using the technique of Very Long Baseline Interferometry (VLBI).
The high sensitivity of this VLBI array in combination with base lengths of different lengts and directions will allow to receive new scientific data on the physics and the turbulence of the interstellar and interplanetary medium, the spatially-temporal structure of non- stationary solar radio sources, the appearance of solar coronal irregularities.
This also will be a first step of the creation of a Ground Telescopes Network for future joint observations with a space VLBI mission. A list of sources for space VLBI will be prepared. The recommendations for the operation of RadioAstron will be made on the basis of scattering effect investigations.
A Low Frequency VLBI Network (LFVN) has been created. The 8 radio telescopes in Russia, Latvia, Ukraine and India were equipped with receiver-recording hardware. Currently, the LFVN is operating at the 327 MHz and 1665 MHz frequency bands with Mk-2 recording terminals and includes the following telescopes: Bear Lakes RT-64 (18 cm and 92 cm) near Moscow, Puschino RT-22 (18 cm and 92 cm) near Moscow, St.Pustyn RT-14 (92 cm) near N.Novgorod and Zimenki RT-15 (92 cm) near N.Novgorod at Russia, Evpatoria RT-70 (92 cm) at Crimea (Ukraine), Torun RT-15 (18 cm and 92 cm) in Poland, ORT (92 cm) at Ooty, India, Urumqi RT-25 (18 cm and 92 cm) in China, and Ventspils RT-32 (92 cm) in Latvia. An Mk2 correlator is developed in the Radiophysical Research Institute, N.Novgorod, Russia. The International Scientific Advisory Council coordinates the LFVN activity. The more detail information about LFVN Project is available from http://lfvn.astronomer.ru/main/lfvn.htm.
A total of 12 VLBI experiments were carried out during 1997-2000, having the scientific goals: (a) pre--launch survey for Space VLBI Radioastron mission, (b) investigation of space medium including solar corona and wind (c) researches of non-stationary solar radio sources - "spikes".
The main results that were obtained are following:
The angular sizes of 60 sources at 327 MHz and 50 sources at 1665 MHz were estimated (the 25 sources were selected as potential targets for future Space VLBI observations at 327 MHz); radio images were constructed for 3C309.1 at both 327 MHz and 1665 MHz, for 3C345 and 3C84 at 327 MHz and PSR0329+54 at 1665 MHz;
the limits, which interplanetary medium puts on the operation of the VLBI-systems at the decimeter wavelength range, were determined (influence of the solar plasma irregularities is essential at the source elongation from the Sun up to 30o at 1665 MHz and up to 80o at 327 MHz, it is still appreciably up to 90o and 140o respectively and for elongation of the sources from the Sun of less then 3o (1665 MHz) and of less then 13o (327 MHz), the phase coherence is disturbed completely;
the existence of average-scale structure of solar wind irregularities in the form of "stream filaments" is suggested, their directions tally with the direction of the solar wind, the cross dimension of such streams is estimated about 1500-2000 km and their longitudinal scale is no less then 100000 km, the irregularities in the region of the separate "streams" are approximately isotropic.
Two solar spike-like events obtained at 18 cm on baseline 118 km (Bear Lakes - Puschino) showed well pronounced interferometric responses. The apparent angular sizes of the relevant solar radio sources are less than 0.5 arc sec. The estimates of the brightness temperature are less than 109 K and 1011 K for the burst durations of 2 sec and 20 msec respectively;
20 "spikes" were detected with ms-time resolution at 540 MHz on baseline 416 m at St. Pustyn, temporal variations of a source position of the radio burst with quasi-periodic sub-second flux pulsations (T = 0.5±0.2 s) were found and it has been shown that the periodicity is connected neither with oscillatory loss-cone instabilities or with an oscillatory electron acceleration mechanism, the peculiarities of that concrete burst agree better with models suggesting that a flare is a combination of quasi-independent "elementary" energy releases occurring in spatially separated non-stable compact regions and as results, the most realistic solar radio spike model was designed.
A new type IIId emission variety having explicit quasi-periodic structure of narrow-band spectral elements has beenfound from solar observation at decameter wavelengths with UTR-2; their complex additional components look like a triple echo. According to amplitude records at the observing frequency of 25 MHz, the initial short radio burst appears to be a weak precursor of a more powerful echo-like burst accompanied by a pair of final pulses somewhat above the background. Nine events of this kind were registered during one type IIId noise storm related to an active region in the central solar longitude sector. The weak Type III bursts with brightness temperatures Tb<107 K (microbursts) were observed.
Properties of propagation and radio emission of fast electron beams in the conditions of the low corona were studied with the aim to explain spike structure of radio emission. It was discovered that high-energy electrons propagate in plasma in the form of a new nonlinear object, beam-plasma structure.
The researches of Solar system bodies by new VLBI Radar method (VLBR) were developed. This method is combined the use of ground radar to provide their visibility at radio frequencies and receiving of reflected echo-signals by array of radio telescopes in VLBI mode. It is allowing to link the sky position of Space body and sky position of source from Radio Reference Frame to define the precise trajectories of movement of Earth group planets and asteroids crossing Earth in quasi-inertial system of coordinates with accuracy up to 0.001". Two pioneer VLBR experiments were carried out with help of planetary radar equipment of Evpatoria RT-70: VLBR99.1 in May 1999 for research of Earth group planets (Mars and Venus), VLBR00.2 in August 2000 for research of two asteroids crossing Earth (Mithra and 2000CE59) and planets Mercury and Venus. The first VLBI fringes confirming the possibility of such kind researches were found for echo-signal reflected by Venus on three baselines Evpatoria - Svetloe - Shanghai.
The first steps in order to organize the International ad-hoc S2 VLBI Array were made. It is planned to joint the RTs with S2 facility in 12 countries for carrying out multi-faceted VLBI researches. The important side of these works will be an integration of large antennas of the NIS with the European VLBI Network.
The Project results were reported 51 times in different scientific conferences and presented in 63 publications.
Mel'nik V.N., Lapshin V.I., Kontar E.P. Propagation of monoenergetic electron beam in the solar corona. Solar Phys. 1999, v.184, pp.353-362
Fleishman G.D., Melnikov V.F. Solar millisecond radio spikes: recent progress, current state, problems for future. - In: Magnetic fields and solar processes, ed. A. Wilson, ESA SP-448, 1999, V.2, PP.1247-1251
Abranin E.P., Bazelyan L.L., Tsybko Ya.G. A new spectral form of decameter Type IIId radio bursts. Observations of superrelativistic, narrow-band radiation sources in the solar vicinity. Izvestia Vuzov. Radiofizika. 1999, v.42, N5, pp.403-417.
Girin I.A., Dementiev A.F., Lipatov B.N., Likhachev S.F., Molotov I.E., Nechaeva M.B., Snegirev S.D., Tikhomirov Yu.V., Chuprikov A.A. VLBI research of fine structure of super compact extragalactic sources and space mediums in the decimetric wavelength band. Izv. VUZov, Radio physics, Vol. XLII, N12, 1999, pp.1127-1135.
Altunin V.I., Dementiev A.F., Lipatov B.N., Netchaeva M.B., Snegirev S.D., Tikhomirov Yu.V., Okmiansky V.A. - Investigations of irregularities of the solar wind plasma by using the VLBI-method on the wavelengths 18 and 90 cm. - Izv.VUZov, Radiofizika, 2000, XLIII, N3, pp.197-206.