Parker Solar Probe detects solar radio bursts related with a behind–the–limb active region

¹ Institute of Radio Astronomy, National Academy of Sciences of Ukraine, Mystetstv St., 4, 61002 Kharkiv, Ukraine
e-mail: a.a.stanislavsky@rian.kharkov.ua
² Faculty of Pure and Applied Mathematics, Hugo Steinhaus Center, Wrocław University of Science and Technology, Wyb. Wyspiańskiego 27, 50-370 Wrocław, Poland
³ V.N. Karazin Kharkiv National University, Svobody Sq., 4, 61022 Kharkiv, Ukraine
⁴ Astronomical Institute of the Czech Academy of Sciences, 251 65 Ondřejov, Czech Republic

Received: 7 August 2021
Accepted: 11 October 2021

Abstract

Context. The interpretation of solar radio bursts observed by Parker Solar Probe (PSP) in the encounter phase plays a key role in understanding intrinsic properties of the emission mechanism in the solar corona. Lower time–frequency resolution of the PSP receiver can be overcome by simultaneous ground–based observations using more advanced antennas and receivers.

Aims. In this paper we present such observations for which the active active region 12 765, begetter of type III, J, and U solar bursts, was within sight of ground–based instruments and behind the solar limb of the PSP spacecraft.

Methods. We used a subarray of the Giant Ukrainian Radio Telescope to get the spectral properties of radio bursts at the frequency range of 8–80 MHz, as well as the PSP radio instruments with a bandwidth of 10.5 kHz–19.2 MHz, during solar observations on June 5, 2020.

Results. We directly detected the radio events initiated by the active region behind the solar limb of the PSP spacecraft, using special conditions in the solar corona, due to the absence of active regions from the PSP side. Following the generation mechanism of solar radio emission, we refined the density model for the solar corona above the active region 12765 responsible for the radio bursts. Based on the PSP spacecraft position near the Sun and delays of radio waves between space– and ground–based records, we found the corresponding radio responses on the PSP spectrogram.

Conclusions. The absence of sunspots from the PSP side contributes to the propagation of radio waves from a dense loop of the Sun to quiet regions with low densities, through which PSP instruments can detect the radiation.