Abstract
To locate two-dimensional positions of the solar decametric radio bursts a heliograph was developed on the basis of the UTR-2 radiotelescope (Khar'kov) operated in the range 10–26 MHz. The beamwidth of the heliograph rapid-scanning pencil-beam is 25 arc min at 25 MHz, and its field of view is about 3.5° (E-W) × 2.0° (N-S). The instrument yields rapidly forty records of the radio brightness of all (8 × 5) elementary parts (each 25 arc min in diameter) of the investigated sky area during every period of 1/4 s. Both coordinates of a burst center are measured with an accuracy 5 arc min. The bandwidth of the receiving system is 10 kHz. The heliograph operates in conjunction with a radiospectrograph connected to the output of a N-S arm of the UTR-2 array. The data observations with the UTR-2 correspond only to one linear polarized component.
The ionospheric distortion of the test records of the radio source Cassiopeia-A that occurred sometimes is illustrated.
First results of 25 MHz observations of the solar radio storm in August, 1976 with the heliograph are presented here. This storm is accompanied by the compact sunspot group travelling all over the optical disk. The type III and stria bursts were predominant during the storm. On the given day the scattering regions of their apparent centers were overlapped and the sizes of these regions were usually not more than 5 arc min. On some days there occurred additional burst sources displaced in position from the persistent storm region. It was found out that, as a rule, 25 MHz stria-bursts from the type IIIb chain coincided in position with the following type III burst at the same frequency. The difference of the daily averaged coordinates of both stria and type III bursts was considerably smaller than the mean diameter of their sources.
The radial distance of the 25 MHz storm region from the solar center was calculated by using the three methods. The storm height was estimated as 1.8R ⊙ from the rotation rate close to the central meridian of the storm center. Definite association of the spots with the storm near the limb allowed to determine the average value 2.1R ⊙ for the height. The limb measurements give the mean height of 2.3R ⊙.
The center-to-limb variation of the storm source height is a known fact in the meter-wavelength range. This is the evidence of the propagation effects in the solar corona being essential to interpret the results of the radio source location.
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Abranin, E.P., Baselyan, L.L., Goncharov, N.Y. et al. Positions of solar storm burst sources by observations with a heliograph based on the UTR-2 antenna at 25 MHz. Sol Phys 66, 393–409 (1980). https://doi.org/10.1007/BF00150593
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DOI: https://doi.org/10.1007/BF00150593