arXiv subjects

Maoshui Lv

Publications and source records attributed to Maoshui Lv.

3 recordsLinked to original sources

arXiv2025

A Flare-related Decimetric Type-IV Radio Burst Induced by the X2 Radiation of Electron Cyclotron Maser Emission

The radiation mechanism of decimetric wideband and pulsating radio bursts from the Sun (in terms of decimetric type-IV (t-IVdm) burst) and other flaring stars is a long-standing problem. Early investigations were based on the leading-spot hypothesis for the sun and yielded contradictory results. Here, we analyzed the flare-associated t-IVdm burst on 20110924 with medium-strong levels of polarization and from sources near a sunspot. We found that the emission is intermittent and the maximum $T_B$ exceeds 10$^{11}$ K, with well-defined upper and lower frequency cutoffs. The radio sources are left-handed polarized, located above the sunspot with a negative polarity. The sources align well with the sites of the second harmonic of the local electron gyrofrequency. These findings provide essential evidence that the burst is induced by the electron cyclotron maser emission (ECME) in the harmonic X mode. We further modeled the transport of downward-streaming energetic electrons along a coronal loop and found most electrons get mirrored within the specific altitude range of 20-100 Mm. This explains why such bursts tend to have well-defined spectral ranges. We also found the ECME-radiating energetic electrons exhibit a shell-like VDF instead of the generally-presumed loss-cone distribution. The study greatly expands the application of ECME in solar radio astronomy and provides solar samples for similar bursts from other flaring stars.

astro-ph.SR↗

arXiv2023

Imaging Preflare Broadband Pulsations in the Decimetric-metric Wavelengths

Preflare activities contain critical information about the pre-cursors and causes of solar eruptions. Here we investigate the characteristics and origin of a group of broadband pulsations (BBPs) in the decimetric-metric wavelengths, taking place during the preflare stage of the M7.1 flare dated on 2011 September 24. The event was recorded by multiple solar instruments including the Nan\c{c}ay Radioheliograh that measure the properties of the radio source. The BBPs start $\sim$24 min before the flare onset, extending from $<$ 360 to above 800 MHz with no discernible spectral drift. The BBPs consist of two stages, during the first stage the main source remains stationary, during the second stage it moves outward along with a steepening extreme-ultraviolet (EUV) wave driven by the eruption of a high-temperature structure. In both stages, we observe frequent EUV brightenings and jets originating from the flare region. During the second stage, the BBPs become denser in number and stronger in general, with the level of the polarization increasing gradually from $<$ 20% to $>$ 60% in the right-handed sense. These observations indicate the steepening EUV wave is important to the BBPs during the second stage, while the preflare reconnections causing the jets and EUV brightenings are important in both stages. This is the first time such a strong association of an EUV wave with BBPs is reported. We suggest a reconnection plus shock-sweeping-across-loop scenario for the cause of the BBPs.

astro-ph.SR↗

arXiv2018

Source Imaging of a Moving Type-IV Solar Radio Burst and its Role in Tracking Coronal Mass Ejection From the Inner to the Outer Corona

Source imaging of solar radio bursts can be used to track energetic electrons and associated magnetic structures. Here we present a combined analysis of data at different wavelengths for an eruption associated with a moving type-IV (t-IVm) radio burst. In the inner corona, the sources are correlated with a hot and twisted eruptive EUV structure, while in the outer corona the sources are associated with the top front of the bright core of a white light coronal mass ejection (CME). This reveals the potential of using t-IVm imaging data to continuously track the CME by lighting up the specific component containing radio-emitting electrons. It is found that the t-IVm burst presents a clear spatial dispersion with observing frequencies. The burst manifests broken power-law like spectra in brightness temperature, which is as high as $10^7$-$10^9$ K while the polarization level is in-general weak. In addition, the t-IVm burst starts during the declining phase of the flare with a duration as long as 2.5 hours. From the differential emission measure analysis of AIA data, the density of the T-IVm source is likely at the level of 10$^8$ cm$^{-3}$ at the start of the burst, and the temperature may reach up to several MK. These observations do not favor gyro-synchrotron to be the radiation mechanism, yet in line with a coherent plasma emission excited by energetic electrons trapped within the source. Further studies are demanded to elucidate the emission mechanism and explore the full diagnostic potential of t-IVm bursts.

astro-ph.SR↗