What specific signature observed in X-ray spectra confirms the passage of the shock front through surrounding gas?

Answer

The presence of highly ionized elements

The extreme heat and ionization deposited by the moving shock front results in specific emission lines from highly ionized elements, providing observational proof of the shock's energy deposition.

What specific signature observed in X-ray spectra confirms the passage of the shock front through surrounding gas?
Elementsupernovashockwave