Sequential Magnetic Reconnections in a Fishbone-like Structure Leading to Recurrent Brightenings

Abstract: The fine-scale release of magnetic free energy in the solar atmosphere is a fundamental open question in solar physics. Multi-wavelength observations at high spatiotemporal resolution now offer a direct window into this process. Using data from NVST, SDO, IRIS, and Hinode, we reveal the energy release process in a fishbone-like magnetic structure within active region 12297. The fishbone-like structure consists of a spine along a narrow, elongated positive-polarity field, with herringbone branches rooted in negative-polarity sunspots. Persistent photospheric magnetic flux emergence and shearing motions are observed beneath the fishbone-like structure, which may play a key role in maintaining its topology and producing the recurrent brightenings. During brightenings, compact bright features propagate sequentially from west to east along the spine, accompanied by bidirectional flows along the branches and plasma blobs ejected toward the distant positive sunspot. These propagating features could be interpreted as signatures of sequential magnetic reconnection events occurring in chronological order at nodes along the spine, predominantly in the chromosphere and transition region. Our observations may provide evidence that recurrent brightenings could arise from repeated sequential reconnection events organized by a coherent magnetic structure, deepening our understanding of how such recurrent brightenings are generated and how magnetic free energy is dissipated at fine scales in solar active regions.