Spectral steepening is a phenomenon observed in astrophysics and astronomy where the spectral index of a source becomes steeper at higher frequencies. This means that the intensity or brightness of the source decreases more rapidly with increasing frequency. Spectral steepening is often seen in objects such as supernova remnants, pulsars, and active galactic nuclei, and can provide important insights into the physical processes at work in these sources. Researchers study spectral steepening to better understand the emission mechanisms and composition of these celestial objects.