Pulsars, transients and relativistic astrophysics

Abstract:

In recent years, certain luminous extragalactic optical transients have been observed to last only a few days¹. Their short observed duration implies a different powering mechanism from the most common luminous extragalactic transients (supernovae), whose timescale is weeks². Some short-duration transients, most notably AT2018cow (ref. ³), show blue optical colours and bright radio and X-ray emission⁴. Several AT2018cow-like transients have shown hints of a long-lived embedded energy source⁵, such as X-ray variability^6,7, prolonged ultraviolet emission⁸, a tentative X-ray quasiperiodic oscillation^9,10 and large energies coupled to fast (but subrelativistic) radio-emitting ejecta^11,12. Here we report observations of minutes-duration optical flares in the aftermath of an AT2018cow-like transient, AT2022tsd (the 'Tasmanian Devil'). The flares occur over a period of months, are highly energetic and are probably nonthermal, implying that they arise from a near-relativistic outflow or jet. Our observations confirm that, in some AT2018cow-like transients, the embedded energy source is a compact object, either a magnetar or an accreting black hole.