AT 2024wpp: An extremely luminous fast ultraviolet transient powered by accretion onto a black hole

Perley, Daniel A., Ho, Anna Y. Q., McGrath, Zoë, Camilo, Michael, Sevilla, Cassie and Inserra, Cosimo ORCID: https://orcid.org/0000-0002-3968-4409 2026. AT 2024wpp: An extremely luminous fast ultraviolet transient powered by accretion onto a black hole. Monthly Notices of the Royal Astronomical Society 549 (1) , stag678. 10.1093/mnras/stag678

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Abstract

We present the discovery of AT 2024wpp (‘Whippet’), a fast and luminous 18cow-like transient. At a redshift of z = 0.0868, revealed by Keck Cosmic Web Imager spectroscopy of its faint star-forming host, it is the fourth-nearest example of its class to date. Rapid identification of the source in the Zwicky Transient Facility data stream permitted ultraviolet-through-optical observations to be obtained prior to peak, allowing the first determination of the peak bolometric luminosity (2 × 1045 erg s−1), maximum photospheric radius (1015 cm), and total radiated energy (1051 erg) of an 18cow-like object. We present results from a comprehensive multiwavelength observing campaign, including a far-UV spectrum from the Cosmic Origins Spectrograph on the Hubble Space Telescope and deep imaging extending >100 days post-explosion from the Very Large Telescope, Hubble Space Telescope, Very Large Array, and Atacama Large Millimetre Array. We interpret the observations under a model in which a rapidly-accreting central engine blows a fast (∼ 0.2 c) wind into the surrounding medium and irradiates it with X-rays. The high Doppler velocities and intense ionization within this wind prevent identifiable spectroscopic features from appearing in the ejecta or in the surrounding circumstellar material. Weak H and He signatures do emerge in the spectra after 35 days in the form of double-peaked narrow lines. Each peak is individually narrow (full width δv ∼ 3000 km s−1) but the two components are separated by Δv ∼ 6600 km s−1, indicating stable structures of denser material, possibly representing streams of tidal ejecta or an ablated companion star.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Schools > Physics and Astronomy
Additional Information:	Full list of authors available at: https://doi.org/10.1093/mnras/stag678
Publisher:	Oxford University Press (OUP)
ISSN:	0035-8711
Date of First Compliant Deposit:	20 April 2026
Date of Acceptance:	7 April 2026
Last Modified:	02 Jun 2026 10:35
URI:	https://orca.cardiff.ac.uk/id/eprint/186494

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