Unprecedented X-Ray Emission from the Fast Blue Optical Transient AT2022tsd

Abstract

We present the X-ray monitoring campaign of AT2022tsd in the time range δ t 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 δ t 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 and marginal evidence at the 3σ confidence level for intrinsic absorption NHint ≈ 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.