Optical Flares in the Luminous Fast Blue Optical Transient AT2022tsd ("Tasmanian Devil")

Abstract: The delayed conversion of a neutron star (NS) into a highly magnetized hybrid star (HS) ejects ~ 0.01Msun of outer NS layers with kinetic energy ~ 10^50 erg (Keranen et al. 2005); the Quark-Nova (QN) ejecta. If this occurs in isolation (or after the SN ejecta had dissipated), the rotational energy of the HS powers a transient with rise and decay times of a few days, consistent with Luminous Fast Blue Optical Transients (LFBOTs) (Ouyed 2025). Breakup of the QN ejecta creates optically thin fragments that release trapped radiation over tens of minutes timescales, producing optical flares with luminosities comparable to the LFBOT peak value. X-ray emission arises from HS spin-down energy leaking through the gradually transparent ejecta, while radio emission is due to synchrotron radiation from the ejecta's interaction with the ambient medium. Our model reproduces key features of AT2022tsd and other LFBOTs, including AT2020xnd, AT2020mrf, and AT2018cow. Flares are absent or dwarfed when fragmentation occurs before or during the LFBOT peak emission phase, as likely in AT2018cow. Our model provides a novel explanation for aged NSs with long spin periods that exhibit youthful magnetar-like activity, such as ASKAP J1832-0911 (Wang et al. 2024). It also carries implications for heavy-element enrichment in the universe, given the formation rate of LFBOTs and the neutron-rich composition of the QN ejecta (Jaikumar et al. 2007, Ouyed et al. 2009).