The disappearance of the helium-giant progenitor of the Type Ib supernova iPTF13bvn and constraints on its companion

We report and discuss post-explosion observations of supernova iPTF13bvn. We find that the brightness of the supernova (SN) at +740 d is below the level of the pre-explosion source and thus confirm that the progenitor has exploded. We estimate that the late-time brightness is still dominated by the SN, which constrains the magnitude and thus mass of a possible companion star to below approximately 10 M_⊙. In turn, this implies that the progenitor's initial mass is constrained to a narrow range between 10 and 12 M_⊙. The progenitor of iPTF13bvn would have been a helium giant rather than a Wolf-Rayet star. In addition, we suggest that sufficiently deep observations acquired in 2016 would now stand a chance to directly observe the companion star.