The Properties of the Host Galaxy and the Immediate Environment of GRB 980425/SN 1998bw from the Multiwavelength Spectral Energy Distribution

We present an analysis of the spectral energy distribution (SED) of the galaxy ESO 184-G82, the host of the closest known long gamma-ray burst (GRB) 980425 and its associated supernova (SN) 1998bw. We use our observations obtained at the Australia Telescope Compact Array (the third >3σ radio detection of a GRB host) as well as archival infrared and ultraviolet (UV) observations to estimate its star formation state. We find that ESO 184-G82 has a UV star formation rate (SFR) and stellar mass consistent with the population of cosmological GRB hosts and of local dwarf galaxies. However, it has a higher specific SFR (per unit stellar mass) than luminous spiral galaxies. The mass of ESO 184-G82 is dominated by an older stellar population in contrast to the majority of GRB hosts. The Wolf-Rayet region ~800 pc from the SN site experienced a starburst episode during which the majority of its stellar population was built up. Unlike that of the entire galaxy, its SED is similar to those of cosmological submillimeter/radio-bright GRB hosts with hot dust content. These findings add to the picture that in general, the environments of GRBs on 1-3 kpc scales are associated with high specific SFR and hot dust.