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

Journal article

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 (LX ≈ 1.5 × 1043 erg s−1), variable X-ray emission with a Compton hump peaking at δt ≈ 50 days. The X-ray spectrum evolves from a soft (Fν ∝ ν−0.6) to an extremely hard state (Fν ∝ ν1.26) 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 L9 GHz ≈ 1.7 × 1029 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 ( Ṁ∼10−3M⊙yr−1 for vw = 1000 km s−1). The inferred outflow velocities increase from Γβc ≈ 0.07c to 0.42c during δt ≈ 32–73 days, indicating an accelerating blast wave. We interpret these observations as a shock propagating through a dense shell of radius ≈1016 cm and then accelerating into a steep density profile ρCSM(r) ∝ r−3.1. All radio-bright LFBOTs exhibit similar circumstellar medium (CSM) density profiles (ρCSM ∝ 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.

Authors: A. J., N; Margutti, R; Wiston, E; Laskar, T; Migliori, G

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: American Astronomical Society
• Journal: The Astrophysical Journal Letters
• Volume: 993
• Issue: 1
• Article number: L6
• Publication date: 2025-10-24
• Acceptance date: 2025-09-20
• DOI: 10.3847/2041-8213/ae0b4d
• EISSN: 2041-8213
• ISSN: 2041-8205
• Language: English
• Keywords: Transient sources; Time domain astronomy; High energy astrophysics