Hot gas around SN 1998bw: Inferring the progenitor from its environment

Spatially resolved spectroscopy of the environments of explosive transients carries detailed information about the physical properties of the stellar population that gave rise to the explosion, and thus the progenitor itself. Here, we present new observations of ESO184-G82, the galaxy hosting the archetype of the γ-ray burst/supernova connection, GRB 980425/SN 1998bw, obtained with the integral field spectrograph MUSE mounted at the Very Large Telescope. These observations have yielded detailed maps of emission-line strength for various nebular lines along with physical parameters such as dust extinction, stellar age, and oxygen abundance on spatial scales of 160 pc. The immediate environment of GRB 980425 is young (5–8 Myr) and consistent with a mildly extinguished (AV ~ 0.1 mag) progenitor of zero-age main-sequence mass between 25 M⊙ and 40 M⊙ and an oxygen abundance 12 + log (O / H) ~ 8.2 (Z ~ 0.3 Z⊙), which is slightly lower than that of an integrated measurement of the whole galaxy (12 + log (O / H) ~ 8.3) and a prominent nearby H i