SN 2024iss: A Multiwavelength Exposé of a Type IIb Supernova with an Early-time Ultraviolet Spectrum and Shock-breakout Constraints

We thank Lars Bildsten, Yan-Fei Jiang, and Matteo Cantiello for valuable discussions regarding the CSM profiles for the 3D SN IIb progenitor model shown in Figure 17. R.J.Y. and F.F. acknowledge support from the Caltech Summer Undergraduate Research Fellowship (SURF) program. W.J.-G. is supported by NASA through Hubble Fellowship grant HST-HF2-51558.001-A, awarded by the Space Telescope Science Institute, which is operated for NASA by the Association of Universities for Research in Astronomy, Inc., under contract NAS5-26555. The UCSC team is supported in part by NASA grant Nos. 80NSSC23K0301 and 80NSSC24K1411, and a fellowship from the David and Lucile Packard Foundation to R.J.F. I.A. is supported by the National Science Foundation award AST-2505775, NASA grant 24-ADAP24-0159, Scialog awards SA-LSST-2024-102a and SA-LSST-2025-112b, and the Discovery Alliance Catalyst Fellowship Mentors award 2025-62192-CM-19. Parts of this research were supported by the Australian Research Council Centre of Excellence for Gravitational Wave Discovery (OzGrav), through project number CE230100016. M.W.C. acknowledges support from the National Science Foundation with grant Nos. PHY-2117997, PHY-2308862, and PHY-2409481. C.G. is supported by a VILLUM FONDEN Villum Experiment grant (VIL69896). A.G. acknowledges the support from the research project grant "Understanding the Dynamic Universe," funded by the Knut and Alice Wallenberg Foundation under Dnr KAW 2018.0067. J.A.G. acknowledges financial support from NASA grant 23-ATP23-0070. J.K. acknowledges support from the National Science Foundation Graduate Research Fellowship Program. C.D.K. gratefully acknowledges support from the NSF through AST-2432037, the HST Guest Observer Program through HST-SNAP-17070 and HST-GO-17706, and from JWST Archival Research through JWST-AR-6241 and JWST-AR-5441. R.M. acknowledges support by the National Science Foundation under award No. AST-2224255. M.R.S. is supported by the STScI Postdoctoral Fellowship. A.S. acknowledges support from the Knut and Alice Wallenberg Foundation through the "Gravity Meets Light" project. S.T. is supported by the Fundamental Fund of Thailand Science Research and Innovation (TSRI) through the National Astronomical Research Institute of Thailand (Public Organization; FFB690078/0269). Q.W. is supported by the Sagol Weizmann-MIT Bridge Program. Based on observations obtained with the Samuel Oschin Telescope 48 inch and the 60 inch Telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. ZTF is supported by the National Science Foundation under grant Nos. AST-1440341 and AST-2034437, and a collaboration including current partners Caltech, IPAC, the Oskar Klein Center at Stockholm University, the University of Maryland, University of California, Berkeley, the University of Wisconsin-Milwaukee, University of Warwick, Ruhr University, Cornell University, Northwestern University, and Drexel University. Operations are conducted by COO, IPAC, and UW. Zwicky Transient Facility access was supported by Northwestern University and the Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA). SED Machine is based upon work supported by the National Science Foundation under grant No. 1106171. The ZTF forced-photometry service was funded under the Heising-Simons Foundation, grant No. 12540303 (PI: Graham). The Gordon and Betty Moore Foundation, through both the Data-Driven Investigator Program and a dedicated grant, provided critical funding for SkyPortal. The Young Supernova Experiment (YSE) and its research infrastructure is supported by the European Research Council under the European Union's Horizon 2020 research and innovation program (ERC Grant Agreement 101002652, PI: K. Mandel), the Heising-Simons Foundation (2018-0913, PI: R. Foley; 2018-0911, PI: R. Margutti), NASA (NNG17PX03C, PI: R. Foley), NSF (AST-1720756, AST-1815935, PI: R. Foley; AST-1909796, AST-1944985, PI: R. Margutti), the David & Lucille Packard Foundation (PI: R. Foley), VILLUM FONDEN (project 16599, PI: J. Hjorth), and the Center for AstroPhysical Surveys (CAPS) at the National Center for Supercomputing Applications (NCSA) and the University of Illinois Urbana-Champaign. Pan-STARRS is a project of the Institute for Astronomy of the University of Hawai'i, and is supported by the NASA SSO Near Earth Observation Program under grant Nos. 80NSSC18K0971, NNX14AM74G, NNX12AR65G, NNX13AQ47G, NNX-08AR22G, and 80NSSC21K1572, and by the State of Hawai'i. The Pan-STARRS1 Surveys (PS1) and the PS1 public science archive have been made possible through contributions by the Institute for Astronomy, the University of Hawai'i, the Pan-STARRS Project Office, the Max-Planck Society and its participating institutes, the Max Planck Institute for Astronomy, Heidelberg and the Max Planck Institute for Extraterrestrial Physics, Garching, The Johns Hopkins University, Durham University, the University of Edinburgh, the Queen's University Belfast, the Harvard-Smithsonian Center for Astrophysics, the Las Cumbres Observatory Global Telescope Network Incorporated, the National Central University of Taiwan, STScI, NASA under grant NNX08AR22G issued through the Planetary Science Division of the NASA Science Mission Directorate, NSF grant AST-1238877, the University of Maryland, Eotvos Lorand University (ELTE), the Los Alamos National Laboratory, and the Gordon and Betty Moore Foundation. This publication has made use of data collected at Lulin Observatory, partly supported by the TAOvA with the NSTC grant 112-2740-M-008-002. We acknowledge the use of public data from the Swift data archive. YSE-PZ was developed by the UC Santa Cruz Transients Team. The UCSC team is supported in part by NASA grant Nos. NNG17PX03C, 80NSSC19K1386, and 80NSSC20K0953; NSF grant Nos. AST-1518052, AST-1815935, and AST-1911206; the Gordon & Betty Moore Foundation; the Heising-Simons Foundation; a fellowship from the David and Lucile Packard Foundation to R.J.F.; Gordon and Betty Moore Foundation postdoctoral fellowships and a NASA Einstein fellowship, as administered through the NASA Hubble Fellowship program and grant HST-HF2-51462.001, to D.O.J.; and a National Science Foundation Graduate Research Fellowship, administered through grant No. DGE-1339067, to D.A.C. Some/all of the data presented in this paper were obtained from the Mikulski Archive for Space Telescopes (MAST) at the Space Telescope Science Institute. The specific observations analyzed can be accessed via doi:10.17909/wqem-3c51. STScI is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. Support to MAST for these data is provided by the NASA Office of Space Science via grant NAG5-7584 and by other grants and contracts. This research is based on observations made with the NASA/ESA Hubble Space Telescope obtained from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with programs HST-GO-17507 (PI: Jacobson-Galan). A major upgrade of the Kast spectrograph on the Shane 3 m telescope at Lick Observatory, led by Brad Holden, was made possible through gifts from the Heising-Simons Foundation, William and Marina Kast, and the University of California Observatories. Research at Lick Observatory is partially supported by a generous gift from Google. The data presented here were obtained in part with ALFOSC, which is provided by the Instituto de Astrofisica de Andalucia (IAA) under a joint agreement with the University of Copenhagen and NOT. The Liverpool Telescope is operated on the island of La Palma by Liverpool John Moores University in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias with financial support from the UK Science and Technology Facilities Council. Some of the data presented herein were obtained at Keck Observatory, which is a private 501(c)3 nonprofit organization operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the Native Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain.