2023RNAAS...7..126M

We present the X-ray monitoring campaign of AT2022tsd in the time range δt_rest = 23-116 days rest-frame since discovery. With an initial 0.3-10 keV X-ray luminosity of L_x ≈ 10⁴⁴ erg s^–1 at δt_rest ≈ 23 days, AT2022tsd is the most luminous FBOT to date and rivals the most luminous GRBs. We find no statistical evidence for spectral evolution. The average X-ray spectrum is well-described by an absorbed simple power-law spectral model with best-fitting photon index ${\rm{\Gamma }}={1.89}_{-0.08}^{+0.09}$ and marginal evidence at the 3σ confidence level for intrinsic absorption NH_int ≈ 4 × 10¹⁹ cm^–2. The X-ray light-curve can be either interpreted as a power-law decay L_x ∝ t^α^ with α ≈ - 2 and superimposed X-ray variability, or as a broken power-law with a steeper post-break decay as observed in other FBOTs such as AT2018cow. We briefly compare these results to accretion models of TDEs and GRB afterglow models.