Synchrotron afterglow model for AT 2022cmc: jetted tidal disruption event or engine-powered supernova?
Abstract
AT 2022cmc is a luminous optical transient (νLν ≳ 1045 erg s-1) accompanied by decaying non-thermal X-rays (peak duration tX ≲ days and isotropic energy EX,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 θj ≃ 0.1 and roughly fixed energy Ej,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 Γj ≲ 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 tX ≲ 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.
- Publication:
-
Monthly Notices of the Royal Astronomical Society
- Pub Date:
- July 2023
- DOI:
- 10.1093/mnras/stad1182
- arXiv:
- arXiv:2301.11939
- Bibcode:
- 2023MNRAS.522.4028M
- Keywords:
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- transients: tidal disruption events;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 11 pages, 9 figures, 2 tables, accepted for publication in MNRAS