Cooling of electrons within the pulsar wind nebula HESS J1825-137. Trend of fitted spectral power-law index with distance, flux from 1 to 5 TeV with distance, and of flux from 1 to 5 TeV with a power-law index from the power-law fits to the spectral boxes depicted in Fig. 8. Correlation coefficients of 0.89 ± 0.06_stat. ± 0.17_sys., − 0.83 ± 0.03_stat. ± 0.01_sys., and − 0.92 ± 0.03_stat. ± 0.4_sys. were found.