The Extraplanar Type II Supernova ASASSN-14jb in the Nearby Edge-on Galaxy ESO 467-G051

Abstract

We present optical photometry and spectroscopy of the Type II supernova ASASSN-14jb, together with VLT MUSE IFU observations of its host galaxy and a nebular-phase spectrum. This SN, in the nearby galaxy ESO 467-G051 ($z=0.006$), was discovered and followed-up by the All Sky Automated Survey for SuperNovae (ASAS-SN). We present LCOGTN $BVgri$ and $Swift$ $w2m1w1ubv$ optical and near-UV/optical light curves and several optical spectra in the early photospheric phase. ASASSN-14jb exploded $\sim 2$ kpc above the star-forming disk of ESO 467-G051, an edge-on disk galaxy. The large projected distance from the disk and non-detection of any H II region in a 1.4 kpc radius in projection are in conflict with the standard environment of core-collapse supernova progenitors and suggests the possible scenario that the progenitor received a kick in a binary interaction. Our analysis yields $D=25\pm 1$ Mpc, $M(^{56}Ni) = 0.0210 \pm 0.0025$ M$_\odot$, $E_{exp}\approx 0.25 \times 10^{51}$ ergs, $M_{ej}\approx 6$ M$_\odot$, and progenitor $R_* = 580 \pm 28$ R$_\odot$, which seems to be consistent with the sub-Solar metallicity of $0.3 \pm 0.1$ Z$_\odot$ derived from the SN spectrum. The nebular spectrum constrains $M_{prog} \simeq 10-12 $ M$_{\odot}$. We discuss the low oxygen abundance of the host galaxy derived from the MUSE data, $12+\log{(O/H)} = 8.27^{+0.16}_{-0.20}$ (O3N2 strong line method), and compare it with the supernova spectra, which is also consistent with a sub-Solar metallicity progenitor. We finally discuss the possible scenarios for the unusual environment for ASASSN-14jb and conclude that either the in-situ star formation or a runaway would imply a low mass progenitor, agreeing with our estimate from the supernova nebular spectrum. We show that the detailed study of the environment can agree with the stronger constrains of the transient observations. (abridged)