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

Understand

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 $\gamma$-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, as well as 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 ($A_V\sim0.1\ \mathrm{mag}$) progenitor of zero-age main-sequence mass between 25 $M_{\odot}$ and 40 $M_{\odot}$ and oxygen abundance 12+log(O/H)~8.2 ($Z\sim0.3\ {Z}_\odot$), which is slightly lower than the one of an integrated measurement of the galaxy (12+log(O/H)~8.3) and a prominent nearby HII region (12+log(O/H)~8.4).