Microwave imaging of quasi-periodic pulsations at flare current sheet

Quasi-periodic pulsations (QPPs; also called quasi-periodic oscillations, i.e., QPOs) are electromagnetic emission phenomena that change quasi-periodically with time. They seem in celestial transient occasions with completely different temporal/spatial scales, reminiscent of stellar flares, gamma ray bursts and quick radio bursts.

The sun, an abnormal star closest to us, is a spot the place flares with QPPs seem regularly. In the usual flare mannequin, magnetic reconnection performs an essential function in releasing vitality from the coronal magnetic area, ejecting plasmoid and accelerating electrons. After escaping from the reconnection area, these energetic electrons propagating alongside magnetic field lines will induce microwave emissions by a gyrosynchrotron mechanism. Thus, the temporal variation of microwave emissions is intently associated to the method of electron acceleration. As soon as the magnetic reconnection occurs quasi-periodically, the electron acceleration can even be quasi-periodic and QPPs will probably be generated.

Within the current paper printed in Nature Communications, Youankun Kou and colleagues describe the brand new imaging commentary of microwave QPPs on the flare present sheet area for the primary time, by utilizing the microwave radioheliograph Expanded Owens Valley Photo voltaic Array (EOVSA) with the state-of-art spectral-imaging functionality.

It has been discovered that the microwave sources on the present sheet are a lot weaker than these at flaring loops, and thus are typically overwhelmed by background noise. Because of EOVSA’s excessive dynamic vary and spectral-imaging functionality, the authors discovered that temporal variations of brightness temperatures and spectral indices (smaller spectral indices, i.e., tougher spectra, similar to larger non-thermal high quality) of all these sources, irrespective of robust or weak, current comparable quasi-periodicities. Furthermore, a 2.5-dimensional MHD simulation additional validates that magnetic islands generated within the present sheet modulate magnetic reconnection right into a quasi-periodic kind.

All these outcomes strongly assist the state of affairs that quasi-periodic magnetic reconnection within the present sheet accelerates electrons quasi-periodically after which generates QPPs.