Core-collapse supernovae (SNe) are the spectacular finale to massive stellar evolution. In this Letter, we identify a progenitor for the nearby core-collapse SN 2012aw in both ground based near-infrared, and space based optical pre-explosion imaging.
The SN itself appears to be a normal Type II Plateau event, reaching a bolometric luminosity of 10$^{42}$ erg s$^{-1}$ and photospheric velocities of $sim$11,000 kms from the position of the H$beta$ P-Cygni minimum in the early SN spectra. We use an adaptive optics image to show that the SN is coincident to within 27 mas with a faint, red source in pre-explosion HST+WFPC2, VLT+ISAAC and NTT+SOFI images. The source has magnitudes $F555W$=26.70$pm$0.06, $F814W$=23.39$pm$0.02, $J$=21.1$pm$0.2, $K$=19.1$pm$0.4, which when compared to a grid of stellar models best matches a red supergiant. Interestingly, the spectral energy distribution of the progenitor also implies an extinction of $A_V>$1.2 mag, whereas the SN itself does not appear to be significantly extinguished. We interpret this as evidence for the destruction of dust in the SN explosion. The progenitor candidate has a luminosity between 5.0 and 5.6 log L/lsun, corresponding to a ZAMS mass between 14 and 26 msun (depending on $A_V$), which would make this one of the most massive progenitors found for a core-collapse SN to date.
We present the detection of the progenitor of the Type II SN 2011dh in archival pre-explosion Hubble Space Telescope images. Using post-explosion Adaptive Optics imaging with Gemini NIRI+ALTAIR, the position of the SN in the pre-explosion images was
determined to within 23mas. The progenitor object was found to be consistent with a F8 supergiant star (log L/L_{odot}=4.92+/-0.20 and T_{eff}=6000+/-280K). Through comparison with stellar evolution tracks, this corresponds to a single star at the end of core C-burning with an initial mass of M_{ZAMS}=13+/-3M_{odot}. The possibility of the progenitor source being a cluster is rejected, on the basis of: 1) the source is not spatially extended; 2) the absence of excess Halpha, emission; and 3) the poor fit to synthetic cluster SEDs. It is unclear if a binary companion is contributing to the observed SED, although given the excellent correspondence of the observed photometry to a single star SED we suggest the companion does not contribute significantly. Early photometric and spectroscopic observations show fast evolution similar to the transitional Type IIb SN 2008ax, and suggest that a large amount of the progenitors hydrogen envelope was removed before explosion.
The observational technique of spectropolarimetry has been used to directly measure the asymmetries of Supernovae (SNe), Gamma-Ray Bursts (GRBs) and X-Ray Flashes (XRFs). We wish to determine if non-axial asymmetries are present in SNe that are assoc
iated with GRBs and XRFs, given the particular alignment of the jet axis and axis of symmetry with the line of sight in these cases. We performed spectropolarimetry with the Very Large Telescope (VLT) FORS1 instrument of the Type Ic SN 2006aj, associated with the XRF 060218, at V-band maximum at 9.6 rest frame days after the detection of the XRF. Due to observations at only 3 retarder plate angles, the data were reduced assuming that the instrumental signature correction for the $U$ Stokes parameter was identical to the correction measured for $Q$. We find SN 2006aj to be highly polarized at wavelengths corresponding to the absorption minima of certain spectral lines, particularly strong for O I 7774AA and Fe II, observed at 4200AA with a polarization 3%. The value of the Interstellar Polarization is not well constrained by these observations and, considering the low polarization observed between 6000-6500AA, the global asymmetry of the SN is $lesssim 15%$. O I and Fe II lines share a polarization angle that differs from Ca II. SN 2006aj exhibits a higher degree of line polarization than other SNe associated with GRBs and XRFs. The polarization associated with spectral lines implies significant asymmetries of these elements with respect to each other and to the line of sight. This is contrary to the standard picture of SNe associated with GRBs/XRFs, where the axis of symmetry of the SN is aligned with the GRB jet axis and the line of sight.
