  The study examines the heating profile of hot solar transition region loops,
particularly focusing on transient brightenings observed in IRIS 1400{\AA}
slit-jaw images. The findings challenge the adequacy of simplistic, singular
heating mechanisms, revealing that the heating is temporally impulsive and
requires a spatially complex profile with multiple heating scales. A forward
modeling code is utilized to generate synthetic IRIS emission spectra of these
loops based on HYDRAD output, confirming that emitting ions are out of
equilibrium. The modeling further indicates that density-dependent dielectronic
recombination rates must be included to reproduce the observed line ratios.
Collectively, this evidence substantiates that the loops are subject to
impulsive heating and that the components of the transiently brightened plasma
are driven far from thermal equilibrium. Heating events such as these are
ubiquitous in the transition region and the analysis described above provides a
robust observational diagnostic tool for characterizing the plasma.
