Decay of a photospheric transient filament at the boundary of a pore and the chromospheric response

Context. The intermediate stages between pores and the formation of sunspots are a rare phenomenon and can be manifested as transient photospheric penumbral-like filaments. Although the magnetic field changes rapidly during the evolution of such filaments, they have not yet been shown to be connected to magnetic reconnection events.Aims. We characterize the evolution of transient photospheric filaments around a pore and search for possible signs of chromospheric responses. Methods. We analyzed observations of a pore in NOAA AR 12739 from the Swedish Solar Telescope, including the spectropolarimetric data of the Fe I 6173 angstrom and the Ca II 8542 angstrom line and spectroscopic data of the Ca II K 3934 angstrom line. The VFISV Milne-Eddington inversion code and the multi-line non-LTE inversion code STiC were utilized to obtain atmospheric parameters in the photosphere and the chromosphere. Results. Multiple filamentary structures of inclined magnetic fields are found in photospheric inclination maps at the boundary of the pore, although the pore had never developed a penumbra. One of the filaments shows a clear counterpart in continuum intensity maps, in addition to photospheric blueshifts. During its decay, a brightening in the blue wing of the Ca II 8542 angstrom line is observed. The Ca II K 3934 angstrom and the Ca II 8542 angstrom lines show complex spectral profiles in this region. Depth-dependent STiC inversion results using data from all available lines yield a temperature increase (roughly 1000 K) and bidirectional flows (magnitudes up to 8 km s(-1)) at log tau=3.5. Conclusions. The temporal and spatial correlations of the decaying filament (observed in the photosphere) to the temperature increase and the bidirectional flows in the high photosphere and low chromosphere suggest that they are connected. We propose scenarios in which magnetic reconnection happens at the edge of a rising magnetic flux tube in the photosphere. This would lead to both the decay of the filament in the photosphere as well as the observed temperature increase and the bidirectional flows in the high photosphere and low chromosphere.

Automated summary

This study observes and analyzes the transient formation of dark filamentary structures in the photosphere, and finds that these structures are connected to magnetic reconnection events. Possible mechanisms of magnetic reconnection are proposed.