Lense-Thirring precessing magnetar engine drives a superluminous supernova.

Abstract

Type I superluminous supernovae (SLSNe-I) are at least an order of magnitude brighter than standard SNe, with the power source for their luminosity still unknown^1-3. The central engines of SLSNe-I are suggested to be magnetars^4,5 but most of the SLSNe-I light curves have several bumps that are unexplained by the standard magnetar model^6-8. Existing explanations for the bumps either modulate the engine luminosity or invoke interactions with circumstellar material (CSM). Surveys of the limited sample of SLSN-I light curves find no compelling evidence favouring either scenario^7,9, leaving both the nature of the light-curve fluctuations and the applicability of the magnetar model unresolved. Here we report high-cadence multiband observations of a SLSN-I with clear 'chirped' (that is, decreasing period) light-curve bumps that can be directly linked to the properties of the magnetar central engine. Our observations are consistent with a magnetar centrally located within the expanding supernova ejecta, surrounded by an infalling accretion disk undergoing Lense-Thirring precession. Our analysis demonstrates that the light curve and bump frequency independently and self-consistently constrain the magnetar spin period to P = 4.2 ± 0.2 ms and the magnetic-field strength to B = (1.6 ± 0.1) × 10¹⁴ G. These results provide the first observational evidence of the Lense-Thirring effect in the environment of a magnetar and confirm the magnetar spin-down model as an explanation for the extreme luminosity observed in SLSNe-I. We anticipate that this discovery will create avenues for testing general relativity in a new regime-the violent centres of young SNe.