Novara, GiovanniGiovanniNovaraESPOSITO, PAOLOPAOLOESPOSITOTIENGO, ANDREAANDREATIENGOVianello, GiacomoGiacomoVianelloSALVATERRA, RubenRubenSALVATERRABELFIORE MONDONI, AndreaAndreaBELFIORE MONDONIDE LUCA, AndreaAndreaDE LUCAD'AVANZO, PaoloPaoloD'AVANZOGreiner, JochenJochenGreinerSCODEGGIO, MARCOMARCOSCODEGGIORosen, SimonSimonRosenDelvaux, CorentinCorentinDelvauxPIAN, ElenaElenaPIANCAMPANA, SergioSergioCAMPANALisini, GianniGianniLisiniMEREGHETTI, SandroSandroMEREGHETTIISRAEL, Gian LucaGian LucaISRAEL2025-02-202025-02-2020200004-637Xhttp://hdl.handle.net/20.500.12386/36106During a search for X-ray transients in the XMM-Newton archive within the EXTraS project, we discovered a new X-ray source that is detected only during an ∼5 min interval of an ∼21 hr-long observation performed on 2011 June 21 (EXMM 023135.0-603743, probability of a random Poissonian fluctuation: ∼1.4 × 10<SUP>-27</SUP>). With dedicated follow-up observations, we found that its position is consistent with a star-forming galaxy (SFR = 1-2 M<SUB>⊙</SUB> yr<SUP>-1</SUP>) at redshift z = 0.092 ± 0.003 (d = 435 ± 15 Mpc). At this redshift, the energy released during the transient event was 2.8 × 10<SUP>46</SUP> erg in the 0.3-10 keV energy band (in the source rest frame). The luminosity of the transient, together with its spectral and timing properties, make EXMM 023135.0-603743 a gripping analog to the X-ray transient associated to SN 2008D, which was discovered during a Swift/XRT observation of the nearby (d = 27 Mpc) supernova-rich galaxy NGC 2770. We interpret the XMM-Newton event as a supernova shock break-out or an early cocoon, and show that our serendipitous discovery is broadly compatible with the rate of core-collapse supernovae derived from optical observations and much higher than that of tidal disruption events.STAMPAenArticle10.3847/1538-4357/ab98f82-s2.0-85089310177https://iopscience.iop.org/article/10.3847/1538-4357/ab98f8https://api.elsevier.com/content/abstract/scopus_id/850893101772020ApJ...898...37NFIS/05 - ASTRONOMIA E ASTROFISICA