A Supernova Candidate at z = 0.092 in XMM–Newton Archival Data
Giovanni Novara, Paolo Esposito, Andrea Tiengo, Giacomo Vianello, Ruben Salvaterra, Andrea Belfiore, Andrea De Luca, Paolo D’Avanzo, Jochen Greiner, Marco Scodeggio, Simon Rosen, Corentin Delvaux, Elena Pian, Sergio Campana, Gianni Lisini, Sandro Mereghetti, G. L. Israel
Abstract
Abstract During 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 −27 ). With dedicated follow-up observations, we found that its position is consistent with a star-forming galaxy (SFR = 1–2 M ⊙ yr −1 ) 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 46 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.