V Krupar, O Kruparova, A Szabo, L Wilson, L Jian, D Lario, T Nieves-Chinchilla, A. Weiss, A Iampietro, H Reid, L Green, E Kontar, R. F. Pinto, K Goetz
Abstract
We report a hectometric (0.5─3 MHz) type IV continuum observed over nearly 19 days (2025 August 21─September 9) in three successive visibility windows as the source corotates with the Sun—first at Solar Orbiter, then 12 days later in the near-Earth sector where Wind and Parker Solar Probe observed overlapping intervals, and finally 1 day later at STEREO-A—indicating a long-lived source that rotates through favorable viewing geometries. During the STEREO-A interval, the continuum is strongly left-hand circularly polarized (∣V/I∣ ≳ 0.9) and quasiperiodic pulsations (45─60 minutes). We interpret these quasiperiodic pulsations as consistent with standing fast-mode MHD oscillations of a large coronal trap. We introduce a single-spacecraft localization technique, the wavevector-corrected ray sphere (WCRS), which applies a correction to direction-finding angles combined with a coronal density model. WCRS places the source near a helmet streamer. Independent size estimates from solar rotation geometry and magnetoseismology are consistent with a transverse diameter of W ≍ 2.5─3.0 R⊙ at the inferred source heights (r ≃ 6─10 R⊙), with the seismology providing a lower bound. The goniopolarimetric apparent half-width at the spacecraft (γ ≍ 20°) exceeds the geometric width by a factor of B∼60±18 , highlighting strong interplanetary scattering. Three fast coronal mass ejections (CMEs) plausibly helped sustain the electron population (e.g., by reorganizing the large-scale trap and/or enabling continued injection from the low corona), maintaining the continuum. This event sets a new duration benchmark for type IV emission and shows that WCRS enables single-spacecraft localization, with potential relevance for operational space weather forecasting, including single-point tracking of CME-driven shocks (type II bursts) and open field connections (type III bursts).
Keywords
Heliosphere / Solar coronal mass ejections / Solar coronal radio emission / Solar radio emission / Solar wind / 711 / 310 / 1993 / 1522 / 1534
The Astrophysical Journal Letters
Volume 1003, Number L5, Page 18
2026 May
