AT2019cmw: A highly luminous, cooling featureless TDE candidate from the disruption of a high mass star in an early-type galaxy

TL;DR

AT2019cmw is an exceptionally luminous, featureless tidal disruption event caused by a high-mass star's disruption near a supermassive black hole, with unique cooling and spectral properties, offering insights into nuclear star formation.

Contribution

This study presents detailed multi-wavelength observations of a rare, luminous, featureless TDE, highlighting its unique photometric evolution and implications for understanding star formation near SMBHs.

Findings

One of the most luminous thermal transients observed.

Features a cooling from 30,000 K to 10,000 K over 300 days.

No X-ray or radio emission detected, constraining jet activity.

Abstract

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 ~$\mathrm{10^{45.6}\,erg\,s^{-1}}$, 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 interpret this event as a `featureless' tidal disruption event (TDE). It displays photometric evolution atypical of most TDEs, cooling from ~30 kK to ~10 kK in the first ~300 days post-peak, with potential implications for future photometric selection of candidate TDEs. No X-ray or radio emission is detected, placing constraints on the presence of on-axis jetted emission or a visible inner-accretion disk. Modelling the optical light curve with existing theoretical prescriptions, we find that AT2019cmw may be the result of 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. This could provide a new window to probe nuclear star formation and the shape of the initial mass function (IMF) in close proximity to SMBHs out to relatively high redshifts.