The Most Luminous Known Fast Blue Optical Transient AT 2024wpp: Unprecedented Evolution and Properties in the X-Rays and Radio

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Abstract We present X-ray (0.3–79 keV) and radio (0.25–203 GHz) observations of the most luminous fast blue optical transient (LFBOT) AT 2024wpp at z = 0.0868, spanning 2–280 days after first light. AT 2024wpp shows luminous ( L X ≈ 1.5 × 10 43 erg s −1 ), variable X-ray emission with a Compton hump peaking at δt ≈ 50 days. The X-ray spectrum evolves from a soft ( F ν ∝ ν −0.6 ) to an extremely hard state ( F ν ∝ ν 1.26 ) accompanied by a rebrightening at δt ≈ 50 days. The X-ray emission properties favor an embedded high-energy source shining through asymmetric expanding ejecta. We detect radio emission peaking at L 9 GHz ≈ 1.7 × 10 29 erg s −1 Hz −1 at δt ≈ 73 days. The spectral evolution is unprecedented: the early millimeter fluxes rise nearly an order of magnitude during δt ≈ 17–32 days, followed by a decline in spectral peak fluxes. We model the radio emission as synchrotron radiation from an expanding blast wave interacting with a dense environment ( M ̇ ∼ 1 0 − 3 M ⊙ yr − 1 for v w = 1000 km s −1 ). The inferred outflow velocities increase from Γ βc ≈ 0.07 c to 0.42 c during δt ≈ 32–73 days, indicating an accelerating blast wave. We interpret these observations as a shock propagating through a dense shell of radius ≈10 16 cm and then accelerating into a steep density profile ρ CSM ( r ) ∝ r −3.1 . All radio-bright LFBOTs exhibit similar circumstellar medium (CSM) density profiles ( ρ CSM ∝ r −3 ), suggesting similar progenitor processes. The X-ray and radio properties favor a progenitor involving super-Eddington accretion onto a compact object launching mildly relativistic disk wind outflows.

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