Unprecedented X-Ray Emission from the Fast Blue Optical Transient AT2022tsd
David Matthews, R. Margutti, Brian D. Metzger, D. Milisavljević, Giulia Migliori, T. Laskar, Daniel Brethauer, E. Berger, R. Chornock, M. R. Drout, E. Ramírez-Ruiz
Abstract
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 ≈ 10 44 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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mi mathvariant="normal">Γ</mml:mi> <mml:mo>=</mml:mo> <mml:msubsup> <mml:mrow> <mml:mn>1.89</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.08</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.09</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> and marginal evidence at the 3 σ confidence level for intrinsic absorption NH int ≈ 4 × 10 19 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.