# Cut-off features in interplanetary solar radio type IV emission

## TL;DR

This study investigates the directivity of solar radio type IV bursts, analyzing three events to understand whether their emission is affected by absorption, emission mechanisms, or propagation effects, especially in relation to associated shock waves and CMEs.

## Contribution

The paper provides new observational evidence linking partial cut-offs in type IV bursts to shock-related phenomena and absorption effects near CME regions.

## Key findings

- Type IV burst emissions can experience partial cut-offs.
- Absorption near shock regions influences burst directivity.
- Associated type II shocks coincide with emission cut-offs.

## Abstract

Solar radio type IV bursts can sometimes show directivity, so that no burst is observed when the source region in located far from the solar disk center. This has recently been verified also from space observations, at decameter wavelengths, using a 3D-view to the Sun with STEREO and Wind satellites. It is unclear whether the directivity is caused by the emission mechanism, by reduced radio wave formation toward certain directions, or by absorption/blocking of radio waves along the line of sight. We present here observations of three type IV burst events that occurred on 23, 25, and 29 July 2004, and originated from the same active region. The source location of the first event was near the solar disk center and in the third event near the west limb. Our analysis shows that in the last two events the type IV bursts experienced partial cut-offs in their emission, that coincided with the appearance of shock-related type II bursts. The type II bursts were formed at the flanks and leading fronts of propagating coronal mass ejections (CMEs). These events support the suggestion of absorption toward directions where the type II shock regions are located.