2023MNRAS.522.4028M

AT 2022cmc is a luminous optical transient (νL_ν ≳ 10⁴⁵ erg s^–1) accompanied by decaying non-thermal X-rays (peak duration t_X ≲ days and isotropic energy E_X,iso ≳ 10⁵³ erg) and a long-lived radio/mm synchrotron afterglow, which has been interpreted as a jetted tidal disruption event (TDE). Both an equipartition analysis and a detailed afterglow model reveal the radio/mm emitting plasma to be expanding mildly relativistically (Lorentz factor $\Gamma \gtrsim \, \mathrm{ few}$ ) with an opening angle θ_j ≃ 0.1 and roughly fixed energy E_j,iso ≳ few × 10⁵³ erg into an external medium of density profile n ∝ R^–k with k ≃ 1.5-2, broadly similar to that of the first jetted TDE candidate Swift J1644+57 and consistent with Bondi accretion at a rate of ∼$10^{-3}\,\dot{M}_{\rm Edd}$ on to a 10⁶ M_⊙ black hole before the outburst. The rapidly decaying optical emission over the first days is consistent with fast-cooling synchrotron radiation from the same forward shock as the radio/mm emission, while the bluer slowly decaying phase to follow likely represents a separate thermal emission component. Emission from the reverse shock may have peaked during the first days, but its non-detection in the optical band places an upper bound Γ_j ≲ 100 on the Lorentz factor of the unshocked jet. Although a TDE origin for AT 2022cmc is indeed supported by some observations, the vast difference between the short-lived jet activity phase t_X ≲ days and the months-long thermal optical emission also challenges this scenario. A stellar core-collapse event giving birth to a magnetar or black hole engine of peak duration ∼1 d offers an alternative model also consistent with the circumburst environment, if interpreted as a massive star wind.