High star cluster formation efficiency in the strongly lensed Sunburst Lyman-continuum galaxy at <i>z</i> = 2.37

We investigate the strongly lensed (\mu x10-100) Lyman continuum (LyC) galaxy, dubbed Sunburst, at z=2.37, taking advantage of a new accurate model lens. A characterization intrinsic (delensed) properties galaxy yields size ~3 sq.kpc, luminosity Muv=-20.3,and stellar mass M~10^9 Msun;16% ultraviolet light is located in 3 Myr old gravitationally-bound young massive star cluster (YMC) with an effective radius Re~8 pc and dynamical ~10^7 Msun (similar to mass), from which LyC radiation detected (\lambda < 912A). The inferred outflowing gas velocity (>300 km/s) exceeds escape cluster. resulting fraction ionizing emerging Sunburst >6-12%, whilst it >46-93% if YMC. 12 additional likely clusters 3~30%, consistent high \Gamma derived local galaxies experiencing extreme physical conditions. presence YMC influences morphology (nucleation), photometry (photometric jumps) spectroscopic output (nebular emission) entire galaxy. de-lensed UV (1600A) magnitudes ~30.6 ~26.9, has m1600~24.8. relatively large rest-frame equivalent width EWrest(Hb+[OIII]4959-5007)~450A emerges contributing ~30%. If O-type stars mainly forged clusters, then such engines were key agents during reionization increasing occurrence EW lines (Hb+[OIII]) observed z>6.5 might be indirect signature reionization.Future facilities (like VLT/MAVIS or ELT), will probe bound on moderately magnified (\mu<5-10) across cosmic epochs up reionization[ABRIDGED]