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Solar UV bursts are small-scale features that exhibit intermittentbrightenings that are thought to be due to magnetic reconnection. They areobserved abundantly in the chromosphere and transition region, in particular inactive regions. We investigate in detail a UV burst related to a magneticfeature that is advected by the moat flow from a sunspot towards a pore. Themoving feature is parasitic in that its magnetic polarity is opposite to thatof the spot and the pore. We used UV spectroscopic and slit-jaw observationsfrom the IRIS to identify and study chromospheric and transition regionspectral signatures of said UV burst. To investigate the magnetic topologysurrounding the UV burst, we used a two-hour-long time sequence of simultaneousline-of-sight magnetograms from the HMI and performed data-driven 3D magneticfield extrapolations by means of a magnetofrictional relaxation technique. Wecan connect UV burst signatures to the overlying EUV coronal loops observed bythe AIA. The UV burst shows a variety of extremely broad line profilesindicating plasma flows in excess of $\pm$200 km s$^{-1}$ at times. The wholestructure is divided into two spatially distinct zones of predominantly up- anddownflows. The magnetic field extrapolations show a persistent fan-spinemagnetic topology at the UV burst. The associated 3D magnetic null point existsat a height of about 500 km above the photosphere and evolves co-spatially withthe observed UV burst. The EUV emission at the footpoints of coronal loops iscorrelated with the evolution of the underlying UV burst. The magnetic fieldaround the null point is sheared by photospheric motions, triggering magneticreconnection that ultimately powers the observed UV burst and energises theoverlying coronal loops. The location of the null point suggests that the burstis triggered low in the solar chromosphere.

Compact solar UV burst triggered in a magnetic field with a fan-spine topology