Kalpha emission of high-Z solid targets irradiated by an intense, short (<100 fs) laser pulse in the 10 keV region is shown to be sensitive to the electron energy cutoff, which is strongly dependent on the density gradient of the plasma corona formed by a long prepulse. The absorption rate of short laser pulses, the hot electron distribution, and x-ray emission from a Cu slab target are studied via a hybrid model, which combines the hydrodynamics, collisional particle-in-cell, and Monte Carlo simulation techniques, and via a direct spectroscopic measurement. An absorption mechanism originating from the interaction of the laser pulse with plasma waves is found to increase the absorption rate by over 30% even for a very short, s-polarized laser pulse. Calculated and measured x-ray spectra are in good agreement, confirming the electron energy cutoff.