We report on multi-wavelength ultraviolet (UV) high-resolution observations taken with the IRIS satellite during the emergence phase of an emerging flux region embedded in the unipolar plage of active region NOAA 12529. These data are complemented by measurements taken with the spectropolarimeter aboard the Hinode satellite and by observations from SDO.
In the photosphere, we observe the appearance of opposite emerging polarities, separating from each other, and cancellation with a pre-existing flux concentration of the plage.
In the upper atmospheric layers, recurrent brightenings resembling UV bursts, with counterparts in all UV/EUV filtergrams, are identified in the EFR site. In addition, plasma ejections are observed at chromospheric level. Most important, we unravel a signature of plasma heated up to 1 MK detecting Fe XII emission in the core of the brightening sites.
Comparing these findings with previous observations and numerical models, we suggest evidence of several long-lasting, small-scale magnetic reconnection episodes between the new bipolar EFR and the ambient field.