The Most Luminous Known Fast Blue Optical Transient AT 2024wpp: Unprecedented Evolution and Properties in the X-Rays and Radio
A. J. Nayana, R. Margutti, Eli Wiston, T. Laskar, Giulia Migliori, R. Chornock, Timothy J. Galvin, Natalie LeBaron, A. Hajela, Collin T. Christy, Itai Sfaradi, D. Tsuna, Olivia Aspegren, Fabio De Colle, Brian D. Metzger, Wenbin Lu, Paz Beniamini, Daniel Kasen, E. Berger, Brian W. Grefenstette, K. D. Alexander, G. C. Anupama, D. L. Coppejans, Luigi F. Cruz, David R. DeBoer, M. R. Drout, Wael Farah, Xiaoshan Huang, W. V. Jacobson-Galán, D. Milisavljević, Alexander W. Pollak, Nathaniel Roth, Huei Sears, Andrew Siemion, Sofia Z. Sheikh, James F. Steiner, Indrek Vurm
Abstract
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 ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover accent="true"> <mml:mi>M</mml:mi> <mml:mo>̇</mml:mo> </mml:mover> <mml:mo>∼</mml:mo> <mml:mn>1</mml:mn> <mml:msup> <mml:mn>0</mml:mn> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>3</mml:mn> </mml:mrow> </mml:msup> <mml:mspace width="0.25em"/> <mml:msub> <mml:mi>M</mml:mi> <mml:mo>⊙</mml:mo> </mml:msub> <mml:mspace width="0.25em"/> <mml:msup> <mml:mi>yr</mml:mi> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:math> 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.