Shock cooling emission from explosions of massive stars – III. Blue supergiants

ABSTRACT Light emission in the first hours and days following core-collapse supernovae is dominated by the escape of photons from the expanding shock-heated envelope. In preceding papers, we provided a simple analytic description of the time-dependent luminosity, L, and colour temperature, $T_{\rm col}$, as well as of the small (${\simeq} 10 {{\, \rm per\, cent}}$) deviations of the spectrum from a blackbody at low frequencies, $h\nu \lt 3T_{\rm col}$, and of ‘line dampening’ at $h\nu \gt 3T_{\rm col}$, for explosions of red supergiants (RSGs) with convective polytropic envelopes (without significant circumstellar medium). Here, we extend our work to provide similar analytic formulae for explosions of blue supergiants with radiative polytropic envelopes. The analytic formulae are calibrated against a large set of spherically symmetric multigroup (frequency-dependent) calculations for a wide range of progenitor parameters (mass, radius, and core/envelope mass ratios) and explosion energies. In these calculations, we use the opacity tables we constructed (and made publicly available), which include the contributions of bound–bound and bound–free transitions. The analytic formulae reproduce the numeric L and $T_{\rm col}$ to within 10 and 5 per cent accuracy, and the spectral energy distribution to within ${\sim} 20\!-\!40 {{\, \rm per\, cent}}$. The accuracy is similar to that achieved for RSG explosions.