The persistent soft X-ray emission from the location of the so-far most luminous supernova ( SN ) , ASASSN-15lh ( or SN 2015L ) , with L \sim 10 ^ { 42 } \mathrm { erg~ { } s ^ { -1 } } , is puzzling . We show that it can be explained by radiation from the SN-shock accelerated electrons inverse-Compton scattering the intense UV photons . The non-detection in radio requires strong free-free absorption in the dense medium . In these interpretations , the circumstellar medium is derived to be a wind ( n \propto R ^ { -2 } ) with mass-loss rate of \dot { M } \gtrsim 3 \times 10 ^ { -3 } M _ { \odot } ( v _ { w } / 10 ^ { 3 } km s ^ { -1 } ) yr ^ { -1 } , and the initial velocity of the bulk SN ejecta is \lesssim 0.02 c . These constraints imply a massive ejecta mass of \gtrsim 60 ( E _ { 0 } / 2 \times 10 ^ { 52 } \mathrm { erg } ) M _ { \odot } in ASASSN-15lh , and a strong wind ejected by the progenitor star within \sim 8 ( v _ { w } / 10 ^ { 3 } km s ^ { -1 } ) ^ { -1 } yrs before explosion .