SN2024iss: A double-peaked Type IIb supernova with evidence of circumstellar interaction

We 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 compared 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. The shock-cooling peak in the V-band light curve reached M_V = -17.33 ± 0.26 mag, while the 56 Ni-powered second peak attained M_V = -17.43 ± 0.26$ mag. Early spectra show a photospheric velocity of approximately 19,400,km,s^-1 at 3.82 days from the Hα P Cygni profile. The Balmer lines persist for at least more than 87 days after the explosion, which is characteristic of 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 ̊m M_⊙ and a radius of 244 ± 43 ̊m R_⊙. Fitting the second light-curve peak with an Arnett-like model indicates a typical ^56Ni mass of 0.117 ± 0.013 ̊m M_⊙ and a relatively low ejecta mass of 1.27 ± 0.34,̊m M_⊙. X-ray observations revealed bright thermal bremsstrahlung emission and indicate a mass-loss rate of $1.6 10^ -5 ̊m M_⊙ yr ^ -1 , which is similar to that of SN,1993J. Supernova,2024iss occupies a transitional position between the two subclasses of extended and compact Type IIb SNe. Its envelope radius and preexplosion mass-loss rate appear to be consistent with the correlation observed in the broader sample. The observational properties of SN,2024iss are compatible with a binary-interaction scenario being the dominant mechanism for envelope stripping.