Abstract
Abstract Magnetic reconnection is a fundamental physical process in various astrophysical, space, and laboratory environments. Many pieces of evidence for magnetic reconnection have been uncovered. However, its specific processes that could be fragmented and turbulent have been short of direct observational evidence. Here, we present observations of a super-hot current sheet during the SOL2017-09-10T X8.2-class solar flare that display the fragmented and turbulent nature of magnetic reconnection. As bilateral plasmas converge toward the current sheet, significant plasma heating and nonthermal motions are detected therein. Two oppositely directed outflow jets are intermittently expelled out of the fragmenting current sheet, whose intensity shows a power-law distribution in the spatial frequency domain. The intensity and velocity of the sunward outflow jets also display a power-law distribution in the temporal frequency domain. The length-to-width ratio of current sheet is estimated to be larger than the theoretical threshold and thus ensures its occurrence. The observations therefore suggest that fragmented and turbulent magnetic reconnection occurs in the long stretching current sheet.
Highlights
Magnetic reconnection, referring to dissipation and connectivity change of magnetic field, is capable of powering plasma heating, plasma motions, and particle acceleration in relativistic jets (Bloom et al 2011), accretion disks (Balbus & Hawley 1998), solar and stellar flares (Sturrock 1966), and magnetospheres (Phan et al 2006)
At ∼15:53 UT, the loop-like structure ascends to a height of 90 Mm and appears as a well defined bubble consisting of a ring-shaped envelop and a low emission cavity, both of which are visible at most Extreme Ultraviolet (EUV) and X-ray passbands
Magnetic reconnection acts as strong coupling between the coronal mass ejections (CMEs) and the flare as indicated by the simultaneity between the evolution of the CME velocity and the variation of the flare emission (Zhang et al 2001)
Summary
Magnetic reconnection, referring to dissipation and connectivity change of magnetic field, is capable of powering plasma heating, plasma motions, and particle acceleration in relativistic jets (Bloom et al 2011), accretion disks (Balbus & Hawley 1998), solar and stellar flares (Sturrock 1966), and magnetospheres (Phan et al 2006). In the Sweet-Parker model, the current sheet is limited to a long and thin region, in which the reconnection proceeds steadily but too slowly to interpret the real energy release rate. Through invoking slow-mode shocks extending from a shortened Sweet-Parker current sheet, the Petschek model is able to significantly boost the reconnection rate (Petschek 1964). The presence of a thin and long hot plasma sheet underneath an erupting CME fits perfectly into the current sheet structure, as predicted in the theoretical model (Lin & Forbes 2000), and the dynamic behaviours of the plasma within and around the current sheet provide direct and solid evidence of a turbulent and intermittent nature of magnetic reconnection
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