An environmental analysis of supernova iPTF13bvn with <i>HST</i> and MUSE

ABSTRACT Searches for supernovae (SNe) progenitors have relied on a direct detection of the star in fortuitous pre-explosion images. We propose an alternative method, using a combination of photometric stellar population fitting alongside integral-field-unit (IFU) spectroscopic analysis of the ionized gas to fully explore the SN environment and constrain the progenitor properties. Isochrone fitting of Hubble Space Telescope (HST)/WFC3 observations reveals the environment of iPTF13bvn contains two stellar populations with unique age ($\tau =\log {t\, \rm {years}}$) and extinction ($A_V$) values, with the closest agreement found between past progenitor studies of iPTF13bvn and our oldest stellar population (P2): $\tau _{P2}=6.97^{+0.06}_{-0.06}$, a corresponding initial mass $M_{\rm {initial},P2} = 20.0\, \rm {M}_\odot$ and $A_{V,P2}=0.53^{+0.10}_{-0.08}\, \rm {mag}$. Further analysis with VLT/MUSE IFU-spectroscopic observations reveals no bright H ii regions associated with iPTF13bvn, suggesting no immediate ongoing star formation. Extinctions derived from the ionized gas are a minimum of $\sim 2.5$ times higher than the resolved stellar population values, assisting in building a 3D picture of the environment. An analysis of the distribution of spaxel extinctions reveals increased variability in the environment of iPTF13bvn, on the edge of a spiral arm. Our study highlights the complex relationship between stars, gas, and dust, and how, when used in a holistic environmental analysis, they can begin to resolve degeneracies that have plagued past progenitor investigations. Specifically for iPTF13bvn, our results support a binary progenitor and a growing consensus for binarity as the predominant mass-loss mechanism for Type Ib SNe progenitors.