CaltechAUTHORS
Published November 1, 2025 | Version Published
Journal Article Open

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

Creators

  • 1. ROR icon University of California, Berkeley
  • 2. ROR icon University of Utah
  • 3. ROR icon Istituto di Radioastronomia di Bologna
  • 4. ATNF, CSIRO Space & Astronomy, P.O. Box 1130, Bentley, WA 6102, Australia
  • 5. ROR icon University of Copenhagen
  • 6. ROR icon University of Arizona
  • 7. ROR icon California Institute of Technology
  • 8. ROR icon University of Tokyo
  • 9. ROR icon National Autonomous University of Mexico
  • 10. ROR icon Columbia University
  • 11. ROR icon Flatiron Institute
  • 12. ROR icon Open University of Israel
  • 13. ROR icon Lawrence Berkeley National Laboratory
  • 14. ROR icon Harvard-Smithsonian Center for Astrophysics
  • 15. ROR icon Indian Institute of Astrophysics
  • 16. ROR icon University of Warwick
  • 17. ROR icon Search for Extraterrestrial Intelligence
  • 18. ROR icon University of Oxford
  • 19. ROR icon University of Toronto
  • 20. ROR icon Purdue University West Lafayette
  • 21. ROR icon Lawrence Livermore National Laboratory
  • 22. ROR icon American University
  • 23. ROR icon Rutgers, The State University of New Jersey
  • 24. ROR icon University of Manchester
  • 25. ROR icon University of Malta
  • 26. ROR icon Tartu Observatory

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 (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 (M ̇∼10−³ M⊙ 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.

Copyright and License

© 2025. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

Acknowledgement

We thank the anonymous referee for feedback. This Letter makes use of the following ALMA data: ADS/JAO.ALMA#2024.A.00003.T and ADS/JAO.ALMA#2024.A.00009.T. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada), MOST and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ. The Allen Telescope Array refurbishment program and its ongoing operations are being substantially funded through the Franklin Antonio Bequest. Additional contributions from Frank Levinson, Greg Papadopoulos, the Breakthrough Listen Initiative, and other private donors have been instrumental in the renewal of the ATA. Breakthrough Listen is managed by the Breakthrough Initiatives, sponsored by the Breakthrough Prize Foundation. The Paul G. Allen Family Foundation provided major support for the design and construction of the ATA, alongside contributions from Nathan Myhrvold, Xilinx Corporation, Sun Microsystems, and other private donors. The ATA has also been supported by contributions from the US Naval Observatory and the US National Science Foundation. We thank the GMRT staff for making these observations possible. The GMRT is run by the National Centre for Radio Astrophysics of the Tata Institute of Fundamental Research. This research has made use of the NuSTAR Data Analysis Software (NuSTARDAS) jointly developed by the ASI Space Science Data Center (SSDC, Italy) and the California Institute of Technology (Caltech, USA). This research has made use of data obtained from the Chandra Data Archive provided by the Chandra X-ray Center (CXC). This Letter employs a list of Chandra data sets, obtained by the Chandra X-ray Observatory, contained in the Chandra Data Collection doi:10.25574/cdc.463. This research has made use of the XRT Data Analysis Software (XRTDAS) developed under the responsibility of the ASI Science Data Center (ASDC), Italy. This work made use of data supplied by the UK Swift Science Data Centre at the University of Leicester. This research has made use of data and software provided by the High Energy Astrophysics Science Archive Research Center (HEASARC), which is a service of the Astrophysics Science Division at NASA/GSFC.

R.M. acknowledges support by the National Science Foundation under award No. AST-2224255 and by NASA under grants 80NSSC22K1587, 80NSSC25K7591, and 80NSSC22K0898. G.M. acknowledges financial support from the INAF mini-grant “The high-energy view of jets and transient” (Bando Ricerca Fondamentale INAF 2022). B.D.M. acknowledges support from NASA AAG (grant No. 80NSSC22K0807), the Fermi Guest Investigator Program (grant No. 80NSSC24K0408), and the Simons Foundation (grant No. 727700). The Flatiron Institute is supported by the Simons Foundation. D.T. is supported by the Sherman Fairchild Postdoctoral Fellowship at Caltech. F.D.C. acknowledges support from the DGAPA/PAPIIT grant IN113424. D.L.C. acknowledges support from the Science and Technology Facilities Council (STFC) grant ST/X001121/1. N.L. thanks the LSST-DA Data Science Fellowship Program, which is funded by LSST-DA, the Brinson Foundation, the WoodNext Foundation, and the Research Corporation for Science Advancement Foundation; her participation in the program has benefited this work. C.T.C. and K.D.A. gratefully acknowledge support from NSF under grant AST-2307668 and from the Alfred P. Sloan Foundation.

Facilities

Swift - Swift Gamma-Ray Burst Mission (XRT and UVOT), AAVSO - American Association of Variable Star Observers International Database, CTIO:1.3m - Cerro Tololo Inter-American Observatory's 1.3 meter Telescope, CTIO:1.5m - Cerro Tololo Inter-American Observatory's 1.5 meter Telescope, CXO - Chandra X-ray Observatory satellite.

Software References

astropy (Astropy Collaboration et al. 2013,2018, 2022).

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Additional details

Related works

Is new version of
Discussion Paper: arXiv:2509.00952 (arXiv)
Is supplemented by
Dataset: 10.25574/cdc.463 (DOI)

Funding

Breakthrough Prize Foundation
National Science Foundation
AST-2224255
National Aeronautics and Space Administration
80NSSC22K1587
National Aeronautics and Space Administration
80NSSC25K7591
National Aeronautics and Space Administration
80NSSC22K0898
National Institute for Astrophysics
National Aeronautics and Space Administration
80NSSC22K0807
National Aeronautics and Space Administration
80NSSC24K0408
Simons Foundation
727700
Sherman Fairchild Foundation
Universidad Nacional Autónoma de México
DGAPA/PAPIIT IN113424
Science and Technology Facilities Council
ST/X001121/1
Vera C. Rubin Observatory
LSST-DA Data Science Fellowship Program -
Brinson Foundation
Research Corporation for Science Advancement
National Science Foundation
AST-2307668
Alfred P. Sloan Foundation

Dates

Accepted
2025-09-20
Available
2025-10-24
Published

Caltech Custom Metadata

Caltech groups
Space Radiation Laboratory , TAPIR , Division of Physics, Mathematics and Astronomy (PMA) , Physics Department
Publication Status
Published