J/A+A/710/A33ivo://CDS.VizieR/J/A+A/710/A33CDSChen L.Wang X.Wu Q.Andrews M.Farah J.Ochner P.Reguitti A.,Filippenko A.V.Brink T.G.Zhang J.Song C.Liu J.Sand D.J.,Albanese I.Alexander K.D.Andrews J.Bostroem K.A.Cai Y.-Z.,Christy C.Esamdin A.Farina A.Franz N.Howell D.A.Hsu B.Hu M.,Iskandar A.Li L.Li G.Li D.Li W.Liu J.Mao Y.McCully C.Mo J.,Newsome M.Qi Ni Y.Pastorello A.Padilla Gonzalez E.Pearson J.,Peng H.Ransome C.Shrestha M.Smith N.Subrayan B.Terreran G.,Valerin G.Vinko J.Vasylyev S.S.Wang L.Wang Z.Wang H.,Wheeler J.C.Wynn K.Xiang D.Yan S.Yuan W.Zhang J.Zheng W.,Zhang Y.2026-05-29T06:59:59Z2026-05-29T07:55:42ZCDS support team

CDS, Observatoire de Strasbourg, 11 rue de l'Universite, F-67000 Strasbourg, France

cds-question@unistra.frsupernovaevisible-astronomybroad-band-photometrysloan-photometryultraviolet-astronomyWe present optical, ultraviolet, and X-ray observations of supernova (SN) 2024iss, a Type IIb SN that shows a prominent double-peaked light curve. We modeled the first peak with a semianalytical shock-cooling model and the X-ray emission with a free-free model. We also compare the envelope radius and mass-loss rate with those of other Type IIb SNe to explore the relationships between the progenitor envelope and the circumstellar material (CSM). The shock-cooling peak in the V-band light curve reached MV=-17.33+/-0.26mag, while the ^56^Ni-powered second peak attained MV=-17.43+/-0.26mag. Early spectra show an photospheric velocity of ~19400km/s at 3.82 days from the H{alpha} P Cygni profile. The Balmer lines persist at least +87 days after the explosion, characterizing hydrogen-rich ejecta. Modeling the first light-curve peak with the shock-cooling model suggests an extended hydrogen envelope with a mass of 0.11+/-0.04M_{sun}_ and a radius of 244+/-43R_{sun}_. Fitting the second light-curve peak with an Arnett-like model indicates a typical 56 Ni mass of 0.117+/-0.013M_{sun}_ and a relatively low ejecta mass of 1.272+/-0.343M_{sun}_. X-ray observations reveal bright thermal bremsstrahlung emission and indicate a mass-loss rate of 1.6x10^-5^M_{sun}_/yr, which is similar to that of SN 1993J. SN 2024iss occupies a transitional position between the two subclasses of extended (eIIb) and compact (cIIb) Type IIb SNe. Its envelope radius and pre-explosion mass-loss rate appear to be correlated, in agreement with theoretical predictions. The observational properties of SN 2024iss are compatible with a binary interaction scenario being the dominant mechanism for envelope stripping. Furthermore, the low column density of neutral hydrogen suggests a compact CSM with an outer radius of <~1.3x10^14^cm, indicating that the progenitor star experienced eruptive mass loss within ~4yr of its terminal explosion.2026A&A...710A..33Chttps://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/710/A33CatalogResearchIsServedByTAP VizieR generic servicehttps://cds.unistra.fr/vizier-org/licences_vizier.htmlhttps://vizier.cds.unistra.fr/viz-bin/VizieR-2?-source=J/A+A/710/A33https://vizier.iucaa.in/viz-bin/VizieR-2?-source=J/A+A/710/A33http://vizieridia.saao.ac.za/viz-bin/VizieR-2?-source=J/A+A/710/A33https://vizier.cds.unistra.fr/viz-bin/votable?-source=J/A+A/710/A33https://vizier.iucaa.in/viz-bin/votable?-source=J/A+A/710/A33http://vizieridia.saao.ac.za/viz-bin/votable?-source=J/A+A/710/A33GETtext/xml+votablehttps://tapvizier.cds.unistra.fr/TAPVizieR/tapUVOpticaldefaultJ/A+A/710/A33/table2Photometric observations of SN 2024issrecnoRecord number assigned by the VizieR team. Should Not be used for identification.meta.recordintMJDModified Julian Date of the observationdtime.epochdoublePhaseTime in days relative to MJD = 60442.21dtime;arith.difffloatFilterPhotometric filter used for the observation (1)instr.setup;instr.filtercharmagObserved apparent magnitude in Filtermagphot.magfloate_magUncertainty of the magnitude measurement in Filtermagstat.error;phot.magfloatInstInstrument used to obtain the datainstr.setupchar