D. A. Perley, A. Ho, Zoë McGrath, Michael Camilo, Cassie Sevilla, P. Chen, Genevieve Schroeder, Taya Govreen-Segal, Aleksandra Bochenek, Yu-Jing Qin, J. H. Gillanders, Benjamin Amend, J. P. Anderson, Igor Andreoni, Amar Aryan, Eric C. Bellm, J. S. Bloom, T. de Boer, Jonathan Carney, Ilaria Caiazzo, Ken C. Chambers, P. Charalampopoulos, Ting-Wan Chen, Tracy X Chen, Eric R. Coughlin, Michael Coughlin, M. Dennefeld, Georgios Dimitriadis, C. Fremling, Danielle Frostig, Avishay Gal-Yam, Lluís Galbany, Anjashay Gangopadhyay, Melzie Ghendrih, M. J. Graham, M. Gromadzki, Steven L Groom, Claudia P Gutiérrez, K-Ryan Hinds, M. E. Huber, C. Inserra, Benjamin C. Kaiser, M. M. Kasliwal, Niilo E Koivisto, Chien-Cheng Lin, Chang Liu, T. Lowe, Eugene Magnier, A. Mahabal, Andrew Milligan, P. Mínguez, Geoffrey Mo, Tomás E Müller-Bravo, M. Nicholl, P. J. Pessi, Giuliano Pignata, Josiah Purdum, Nabeel Rehemtulla, R Michael Rich, Anwesha Sahu, Avinash Singh, S. J. Smartt, Ian A Smith, J. Sollerman, Gokul P. Srinivasaragavan, Shubham Srivastav, Robert D Stein, S. Schulze, Jack W. Tweddle, R. Wainscoat, J. Wise, Lin Yan, D. W. Young
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 ($2\times 10^{45}$ erg s$^{-1}$), maximum photospheric radius ($10^{15}$ cm), and total radiated energy ($10^{51}$ erg) of an 18cow-like object. We present results from a comprehensive multiwavelength observing campaign, including a far-ultraviolet spectrum from the Cosmic Origins Spectrograph on the Hubble Space Telescope and deep imaging extending $\,\gt\,$100 d post-explosion from the Very Large Telescope, Hubble Space Telescope, Very Large Array, and Atacama Large Millimetre Array. We interpret the observations under a model in which a rapidly accreting central engine blows a fast ($\sim$ 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 d in the form of double-peaked narrow lines. Each peak is individually narrow (full width $\delta v \sim 3000$ km s$^{-1}$) but the two components are separated by $\Delta v \sim 6600$ km s$^{-1}$, indicating stable structures of denser material, possibly representing streams of tidal ejecta or an ablated companion star.