We present an unprecedented high-resolution H \alpha imaging spectroscopic observation of a C4.1 flare taken with the Interferometric Bidimensional Spectrometer ( IBIS ) in conjunction with the adaptive optics system at the 76 cm Dunn Solar Telescope on 2011 October 22 in active region NOAA 11324 .
Such a two-dimensional spectroscopic observation covering the entire evolution of a flare ribbon with high spatial ( 0.1 ^ { \prime \prime } pixel ^ { -1 } image scale ) , cadence ( 4.8 s ) and spectral ( 0.1 Å stepsize ) resolution is rarely reported .
The flare consists of a main circular ribbon that occurred in a parasitic magnetic configuration and a remote ribbon that was observed by the IBIS .
Such a circular-ribbon flare with a remote brightening is predicted in 3D fan-spine reconnection but so far has been rarely observed .

During the flare impulsive phase , we define “ core ” and “ halo ” structures in the observed ribbon based on IBIS narrowband images in the H \alpha line wing and line center .
Examining the H \alpha emission spectra averaged in the flare core and halo areas , we find that only those from the flare cores show typical nonthermal electron beam heating characteristics that have been revealed by previous theoretical simulations and observations of flaring H \alpha line profiles .
These characteristics include : broad and centrally reversed emission spectra , excess emission in the red wing with regard to the blue wing ( i.e. , red asymmetry ) , and redshifted bisectors of the emission spectra .
We also observe rather quick timescales for the heating ( \sim 30 s ) and cooling ( \sim 14–33 s ) in the flare core locations .
Therefore , we suggest that the flare cores revealed by IBIS track the sites of electron beam precipitation with exceptional spatial and temporal resolution .
The flare cores show two-stage motion ( a parallel motion along the ribbon followed by an expansion motion perpendicular to the ribbon ) during the two impulsive phases of the flare .
Some cores jump quickly ( 30 km s ^ { -1 } ) between discrete magnetic elements implying reconnection involving different flux tubes .
We observe a very high temporal correlation ( \gtrsim 0.9 ) between the integrated H \alpha and HXR emission during the flare impulsive phase .
A short time delay ( 4.6 s ) is also found in the H \alpha emission spikes relative to HXR bursts .
The ionization timescale of the cool chromosphere and the extra time taken for the electrons to travel to the remote ribbon site may contribute to this delay .