Progenitors of supernova Ibc: a single Wolf-Rayet star as the possible progenitor of the SN Ib iPTF13bvn

Abstract

Core-collapse supernova (SN) explosions mark the end of the tumultuous life of massive stars. Determining the nature of their progenitors is a crucial step towards understanding the properties of SNe. Until recently, no progenitor has been directly detected for SN of type Ibc, which are believed to come from massive stars that lose their hydrogen envelope through stellar winds and from binary systems where the companion has stripped the H envelope from the primary. Here we analyze recently reported observations of iPTF13bvn, which could possibly be the first detection of a SN Ib progenitor based on pre-explosion images. Very interestingly, the recently published Geneva models of single stars can reproduce the observed photometry of the progenitor candidate and its mass-loss rate, confirming a recently proposed scenario. We find that a single WR star with initial mass in the range 31-35 M fits the observed photometry of the progenitor of iPTF13bvn. The progenitor likely has a luminosity of log (L /L ) ∼ 5.55, surface temperature ∼45 000 K, and mass of ∼10.9 M at the time of explosion. Our non-rotating 32 M model overestimates the derived radius of the progenitor, although this could likely be reconciled with a fine-tuned model of a more massive (between 40 and 50 M ), hotter, and luminous progenitor. Our models indicate a very uncertain ejecta mass of ∼8 M , which is higher than the average of the SN Ib ejecta mass that is derived from the lightcurve (2-4 M ). This possibly high ejecta mass could produce detectable effects in the iPTF13bvn lightcurve and spectrum. If the candidate is indeed confirmed to be the progenitor, our results suggest that stars with relatively high initial masses (>30 M ) can produce visible SN explosions at their deaths and do not collapse directly to a black hole.

The rise and fall of the Type Ib supernova iPTF13bvn

“…Lacking spectra of iPTF13bvn in the nebular phase, we can instead use the r -band photometry from the NOT obtained at M ZAMS = 17 M (Jerkstrand et al 2014b). Thus, we find that the late-time oxygen line luminosity of iPTF13bvn is not consistent with that expected from the M ZAMS = 32 M progenitor suggested by Groh et al (2013a).…”

“…Cao et al (2013) reported the absolute (Vega) magnitudes for this source: M B = −5.52 ± 0.39, M V = −5.55 ± 0.39, and M I = −5.77 ± 0.41 mag. These are consistent with a single WR star (Eldridge et al 2013;Groh et al 2013a). However, Cao et al (2013) also caution that other scenarios (e.g., a binary system, or a small cluster) can result in similar colors and absolute magnitudes.…”

“…For the massive single-star progenitor scenario proposed by Groh et al (2013a), a large O mass is expected, and our observations allow us to test this.…”

“…We note that while it could be argued that a significant part of the He core could fall back onto the central compact object, such a scenario that still produces an apparently nickel-powered LC, normal observed photospheric velocities, and the measured oxygen emission appears unlikely. We also note that while the deduced high mass-loss rate was interpreted by Groh et al (2013a) as favoring a massive WR star, the mass-loss estimate depends on an assumed high stellar wind velocity. A lower wind velocity in combination with the radio measurements of Cao et al (2013) can also be consistent with a less massive star.…”

“…The corresponding mass of the He core of the progenitor is ∼3.4 M immediately prior to the explosion. The synthesized 12 The total He-core mass of the progenitor proposed by Groh et al (2013a) immediately prior to the explosion is 10.9 M . 13 We do not fit for the photospheric velocities at times later than +40 d. Our model of the photosphere is not applicable at these times.…”