Observations spanning a large wavelength range , from X-ray to radio , of the Type IIb supernova 2011hs are presented , covering its evolution during the first year after explosion .
The optical light curve presents a narrower shape and a fainter luminosity at peak than previously observed for Type IIb SNe .
High expansion velocities are measured from the broad absorption H I and He I lines .
From the comparison of the bolometric light curve and the time evolution of the photospheric velocities with hydrodynamical models , we found that SN 2011hs is consistent with the explosion of a 3–4 M _ { \odot } He-core progenitor star , corresponding to a main sequence mass of 12–15 M _ { \odot } , that ejected a mass of ^ { 56 } Ni of about 0.04 M _ { \odot } , with an energy of E = 8.5 \times 10 ^ { 50 } erg .
Such a low-mass progenitor scenario is in full agreement with the modelling of the nebular spectrum taken at \sim 215 days from maximum .
From the modelling of the adiabatic cooling phase , we infer a progenitor radius of \approx 500–600 R _ { \odot } , clearly pointing to an extended progenitor star .
The radio light curve of SN 2011hs yields a peak luminosity similar to that of SN 1993J , but with a higher mass loss rate and a wind density possibly more similar to that of SN 2001ig .
Although no significant deviations from a smooth decline have been found in the radio light curves , we can not rule out the presence of a binary companion star .