  We present an analysis of the electron dynamics during rapid island merging
in asymmetric magnetic reconnection. We consider a doubly periodic system with
two asymmetric transitions. The upper layer is an asymmetric Harris sheet
initially perturbed to promote a single reconnection site. The lower layer is a
tangential discontinuity that promotes the formation of many X-points,
separated by rapidly merging islands. Across both layers the magnetic field and
the density have a strong jump, but the pressure is held constant. Our analysis
focuses on the consequences of electron energization during island coalescence.
We focus first on the parallel and perpendicular components of the electron
temperature to establish the presence of possible anisotropies and
non-gyrotropies. Thanks to the direct comparison between the two different
layers simulated, we can distinguish three main types of behavior
characteristic of three different regions of interest. The first type
represents the regions where traditional asymmetric reconnections take place
without involving island merging. The second type of regions instead show
reconnection events between two merging islands. Finally, the third regions
identifies the regions between two diverging island and where typical signature
of reconnection is not observed. Electrons in these latter regions additionally
show a flat-top distribution resulting from the saturation of a two-stream
instability generated by the two interacting electron beams from the two
nearest reconnection points. Finally, the analysis of agyrotropy shows the
presence of a distinct double structure laying all over the lower side facing
the higher magnetic field region. The distinguishing features found for the
three types of regions investigated provide clear indicators to the recently
launched MMS NASA mission for investigating magnetopause reconnection involving
multiple islands.
