Radio Signature of a Distant behind-the-limb CME on 2017 September 6

We discuss properties of a Type IV burst, which was observed on 2017 September 6, as a result of the powerful flare X 9.3. At decameter wavelengths this burst was observed by the radio telescopes STEREO A, URAN-2, and the Nancay Decameter Array at frequencies 5–35 MHz. This moving Type IV burst was associated with a coronal mass ejection (CME) propagating in the southwest direction with a speed of 1570 km s⁻¹. The maximum radio flux of this burst was about 300 s.f.u. and the polarization was more than 40%. In the frequency range of 8–33 MHz it continued for more than 2 hr. For STEREO A the associated CME was behind the limb, and its longitudinal angle was about 160°. This moving Type IV burst was observed by STEREO A at frequencies of 5–15 MHz in spite of the low sensitivity of STEREO A. This means that the radio emission directivity of a Type IV burst is rather wide. Assuming the plasma mechanism of Type IV radio emission we derived the plasma density distribution in the CME core at distances of 5.6 R_s and 9.8 R_s (R_s is the solar radius), and its mass to be about 10¹⁶ g. It is planned that the minimum perihelion of the Parker Solar Probe (PSP) spacecraft will be at about 9 R_s. So we discuss in what conditions PSP will be in if it crosses a similar CME core.