  Penumbral microjets are short-lived, fine-structured and bright jets that are
generally observed in chromospheric imaging of the penumbra of sunspots. Here
we investigate their potential transition region signature, by combining
observations with the Swedish 1-m Solar Telescope (SST) in the Ca II H and Ca
II 8542{\AA} lines with ultraviolet imaging and spectroscopy obtained with the
Interface Region Imaging Spectrograph (IRIS), which includes the C II
1334/1335{\AA}, Si IV 1394/1403{\AA} and Mg II h & k 2803/2796{\AA} lines. We
find a clear corresponding signal in the IRIS Mg II k, C II and Si IV slit-jaw
images, typically offset spatially from the Ca II signature in the direction
along the jets: from base to top, the penumbral microjets are predominantly
visible in Ca II, Mg II k and C II/Si IV, suggesting progressive heating to
transition region temperatures along the jet extent. Hence, these results
support the suggestion from earlier studies that penumbral microjets may heat
to transition region temperatures.
