Description
We present Optical/UV photometric and spectroscopic observations, as well as X-ray and radio follow-up, of the extraordinary event AT2019cmw. With a peak bolometric luminosity of ~10^45.6 erg/s, it is one of the most luminous thermal transients ever discovered. Extensive spectroscopic follow-up post-peak showed only a featureless continuum throughout its evolution. This, combined with its nuclear location, blue colour at peak and lack of prior evidence of an AGN in its host lead us to classify this event as a “featureless” tidal disruption event (TDE). It displays blackbody evolution atypical of most TDEs, cooling from ~30kK to ~10kK in the first ~300 days post-peak, with potential implications for future photometric selection of candidate TDEs. We also do not find significant evidence of X-ray or Radio emission, placing constraints on the presence of on-axis jetted emission or visible inner-accretion disk. Our lightcurve modelling suggests that AT2019cmw may be the disruption of a star in the tens of solar masses by a supermassive black hole (SMBH). Combined with a lack of detectable star formation in its host galaxy, it could imply the existence of a localised region of star formation around the SMBH. With the expected discovery of >35000 TDEs by the upcoming Vera C. Rubin Observatory, this could provide a new window to probe star formation rates and the initial mass function (IMF) in close proximity to SMBHs out to relatively high redshifts.
