We discovered Bowen emission arising from a strongly lensed ( \mu > 20 ) transient stellar object hosted in the Sunburst arc at z=2.37 . Unique ultraviolet lines emerge at the location of the transient . In particular , narrow ( \sigma _ { v } \simeq 40 km s ^ { -1 } ) ionisation lines of several chemical species ( Fe , C , Si ) fluoresce after being exposed to Lyman series ( e.g. , Ly \alpha , Ly \beta ) of H , He i and He ii that pump selectively their atomic levels . Similarities with the Resonance-Enhanced Two Photon-Ionisation ( RETPI ) spectral features observed in the circum-stellar Weigelt blobs of Eta Carinae are observed . Data from VLT/MUSE , X-Shooter and ESPRESSO observations ( the latter placed at the focus of the four UTs ) at increasing spectral resolution of R=2500 , 11400 and R=70000 , respectively , confirm the lasing action since at least 3.3 years ( \simeq 1 year rest-frame ) , and probe the circum-stellar dense gas condensations in radiation-rich conditions . We discuss the physical origin of the transient event , which remains unclear . We expect such transient events ( including also supernova or impostors ) will be easily recognised with ELTs thanks to high angular resolution provided by adaptive optics and large collecting area , especially in modest ( \mu < 3 ) magnification regime .