Bidirectional outflows as evidence of magnetic reconnection leading to a solar microflare

Abstract

Magnetic reconnection is a rapid energy release process that is believed to be responsible for flares on the Sun and stars. Nevertheless, such flare-related reconnection is mostly detected to occur in the corona, while there have been few studies concerning the reconnection in the chromosphere or photosphere. Here we present both spectroscopic and imaging observations of magnetic reconnection in the chromosphere leading to a microflare. During the flare peak time, chromospheric line profiles show significant blueshifted/redshifted components on the two sides of the flaring site, corresponding to upflows and downflows with velocities of $\pm$(70--80) km s${}^{-1}$, comparable with the local Alfvén speed as expected by the reconnection in the chromosphere. The three-dimensional nonlinear force-free field configuration further discloses twisted field lines (a flux rope) at a low altitude, cospatial with the dark threads in He I 10830 Å images. The instability of the flux rope may initiate the flare-related reconnection. These observations provide clear evidence of magnetic reconnection in the chromosphere and show the similar mechanisms of a microflare to those of major flares.

arXiv comment16 pages, 5 figures, accepted for publication in ApJL

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• IRIS Si IV Line Profiles at Flare Ribbons as Indications of Chromospheric Condensation
• Transition-region explosive events produced by plasmoid instability
• Multi-wavelength Observation of a Failed Eruption from a Helical Kink-unstable Prominence
• Ca II 8542 Å brightenings induced by a solar microflare
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• Chromospheric Inversions of a Micro-flaring Region
• Three-dimensional Magnetic and Thermodynamic Structures of Solar Microflares
• Decay of a photospheric transient filament at the boundary of a pore and the chromospheric response