  A wide variety of phenomena such as gentle but persistent brightening,
dynamic slender features (~100 km), and compact (~1'') ultraviolet (UV) bursts
are associated with the heating of the solar chromosphere. High spatio-temporal
resolution is required to capture the finer details of the likely magnetic
reconnection-driven, rapidly evolving bursts. Such observations are also needed
to reveal their similarities to large-scale flares, which are also thought to
be reconnection driven, and more generally their role in chromospheric heating.
Here we report observations of chromospheric heating in the form of a UV burst
obtained with the balloon-borne observatory, SUNRISE. The observed burst
displayed a spatial morphology similar to that of a large-scale solar flare
with circular ribbon. While the co-temporal UV observations at 1.5'' spatial
resolution and 24s cadence from the Solar Dynamics Observatory showed a compact
brightening, the SUNRISE observations at diffraction-limited spatial resolution
of 0.1'' at 7s cadence revealed a dynamic sub-structure of the burst that it is
composed of extended ribbon-like features and a rapidly evolving arcade of thin
(~0.1'' wide) magnetic loop-like features, similar to post-flare loops. Such a
dynamic sub-structure reveals the small-scale nature of chromospheric heating
in these bursts. Furthermore, based on magnetic field extrapolations, this
heating event is associated with a complex fan-spine magnetic topology. Our
observations strongly hint at a unified picture of magnetic heating in the
solar atmosphere from some large-scale flares to small-scale bursts, all being
associated with such a magnetic topology.
