We report and discuss post-explosion observations of supernova iPTF13bvn. We find that the brightness of the supernova (SN) at +740 d is below the level of the pre-explosion source and thus confirm ...that the progenitor has exploded. We estimate that the late-time brightness is still dominated by the SN, which constrains the magnitude and thus mass of a possible companion star to below approximately 10 M⊙. In turn, this implies that the progenitor's initial mass is constrained to a narrow range between 10 and 12 M⊙. The progenitor of iPTF13bvn would have been a helium giant rather than a Wolf–Rayet star. In addition, we suggest that sufficiently deep observations acquired in 2016 would now stand a chance to directly observe the companion star.
We present the results of a 10.5-yr, volume-limited (28-Mpc) search for supernova (SN) progenitor stars. In doing so we compile all SNe discovered within this volume (132, of which 27 per cent are ...Type Ia) and determine the relative rates of each subtype from literature studies. The core-collapse SNe break down into 59 per cent II-P and 29 per cent Ib/c, with the remainder being IIb (5 per cent), IIn (4 per cent) and II-L (3 per cent). There have been 20 II-P SNe with high-quality optical or near-infrared pre-explosion images that allow a meaningful search for the progenitor stars. In five cases they are clearly red supergiants, one case is unconstrained, two fall on compact coeval star clusters and the other twelve have no progenitor detected. We review and update all the available data for the host galaxies and SN environments (distance, metallicity and extinction) and determine masses and upper mass estimates for these 20 progenitor stars using the stars stellar evolutionary code and a single consistent homogeneous method. A maximum likelihood calculation suggests that the minimum stellar mass for a Type II-P to form is mmin= 8.5+1−1.5 M⊙ and the maximum mass for II-P progenitors is mmax= 16.5 ± 1.5 M⊙, assuming a Salpeter initial mass function holds for the progenitor population (in the range Γ=−1.35+0.3−0.7). The minimum mass is consistent with current estimates for the upper limit to white dwarf progenitor masses, but the maximum mass does not appear consistent with massive star populations in Local Group galaxies. Red supergiants in the Local Group have masses up to 25 M⊙ and the minimum mass to produce a Wolf–Rayet star in single star evolution (between solar and LMC metallicity) is similarly 25–30 M⊙. The reason we have not detected any high-mass red supergiant progenitors above 17 M⊙ is unclear, but we estimate that it is statistically significant at 2.4σ confidence. Two simple reasons for this could be that we have systematically underestimated the progenitor masses due to dust extinction or that stars between 17–25 M⊙ produce other kinds of SNe which are not II-P. We discuss these possibilities and find that neither provides a satisfactory solution. We term this discrepancy the ‘red supergiant problem’ and speculate that these stars could have core masses high enough to form black holes and SNe which are too faint to have been detected. We compare the 56Ni masses ejected in the SNe to the progenitor mass estimates and find that low-luminosity SNe with low 56Ni production are most likely to arise from explosions of low-mass progenitors near the mass threshold that can produce a core-collapse.
The progenitors of many Type II core-collapse supernovae (SNe) have now been identified directly on pre-discovery imaging. Here, we present an extensive search for the progenitors of Type Ibc SNe in ...all available pre-discovery imaging since 1998. There are 12 Type Ibc SNe with no detections of progenitors in either deep ground-based or Hubble Space Telescope archival imaging. The deepest absolute BVR magnitude limits are between −4 and − 5 mag. We compare these limits with the observed Wolf-Rayet population in the Large Magellanic Cloud and estimate a 16 per cent probability that we have failed to detect such a progenitor by chance. Alternatively, the progenitors evolve significantly before core-collapse or we have underestimated the extinction towards the progenitors. Reviewing the relative rates and ejecta mass estimates from light-curve modelling of Ibc SNe, we find both incompatible with Wolf-Rayet stars with initial masses >25 M being the only progenitors. We present binary evolution models that fit these observational constraints. Stars in binaries with initial masses 20 M lose their hydrogen envelopes in binary interactions to become low-mass helium stars. They retain a low-mass hydrogen envelope until 104 yr before core-collapse; hence, it is not surprising that Galactic analogues have been difficult to identify.
We present late-time Hubble Space Telescope ultraviolet (UV) and optical observations of the site of SN 2011dh in the galaxy M51, ∼1164 days post-explosion. At the supernova (SN) location, we ...observe a point source that is visible at all wavelengths, which is significantly fainter than the spectral energy distribution (SED) of the yellow supergiant progenitor observed prior to explosion. The previously reported photometry of the progenitor is, therefore, completely unaffected by any sources that may persist at the SN location after explosion. In comparison with the previously reported late-time photometric evolution of SN 2011dh, we find that the light curve has plateaued at all wavelengths. The SED of the late-time source is clearly inconsistent with an SED of stellar origin. Although the SED is bright at UV wavelengths, there is no strong evidence that the late-time luminosity originates solely from a stellar source corresponding to the binary companion, although a partial contribution to the observed UV flux from a companion star cannot be ruled out.
ABSTRACT
We predict linear polarization for a radioactively powered kilonova following the merger of a black hole and a neutron star. Specifically, we perform 3D Monte Carlo radiative transfer ...simulations for two different models, both featuring a lanthanide-rich dynamical ejecta component from numerical-relativity simulations while only one including an additional lanthanide-free disc-wind component. We calculate polarization spectra for nine different orientations at 1.5, 2.5, and 3.5 d after the merger and in the $0.1\!-\!2\, \mu$m wavelength range. We find that both models are polarized at a detectable level 1.5 d after the merger while show negligible levels thereafter. The polarization spectra of the two models are significantly different. The model lacking a disc wind shows no polarization in the optical, while a signal increasing at longer wavelengths and reaching $\sim 1\!-\!6{{\ \rm per\ cent}}$ at $2\, \mu$m depending on the orientation. The model with a disc-wind component, instead, features a characteristic ‘double-peak’ polarization spectrum with one peak in the optical and the other in the infrared. Polarimetric observations of future events will shed light on the debated neutron richness of the disc-wind component. The detection of optical polarization would unambiguously reveal the presence of a lanthanide-free disc-wind component, while polarization increasing from zero in the optical to a peak in the infrared would suggest a lanthanide-rich composition for the whole ejecta. Future polarimetric campaigns should prioritize observations in the first ∼48 h and in the $0.5\!-\!2\, \mu$m range, where polarization is strongest, but also explore shorter wavelengths/later times where no signal is expected from the kilonova and the interstellar polarization can be safely estimated.
We present the detection of the putative progenitor of the Type IIb SN 2011dh in archival pre-explosion Hubble Space Telescope images. Using post-explosion Adaptive Optics imaging with Gemini ...NIRI+ALTAIR, the position of the supernova (SN) in the pre-explosion images was determined to within 23 mas. The progenitor candidate is consistent with an F8 supergiant star (logL/L = 4.92 ? 0.20 and T eff = 6000 ? 280 K). 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 ? 3 M . The possibility of the progenitor source being a cluster is rejected, on the basis of: (1) the source not being spatially extended, (2) the absence of excess H Delta *a emission, and (3) the poor fit to synthetic cluster spectral energy distributions (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 that 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 progenitor's hydrogen envelope was removed before explosion. Late-time observations will reveal if the yellow supergiant or the putative companion star were responsible for this SN explosion.
The quasar Q0918+1636 (z = 3.07) has two intervening high-metallicity Damped Lyman α Absorbers (DLAs) along the line of sight, at redshifts of z = 2.412 and 2.583. The z = 2.583 DLA is located at a ...large impact parameter of 16.2 kpc, and despite this large impact parameter it has a very high metallicity (consistent with solar), a substantial fraction of H2 molecules and it is dusty as inferred from the reddened spectrum of the background QSO. The z = 2.412 DLA has a metallicity of M/H = −0.6 (based on Zn ii and Si ii). In this paper we present new observations of this interesting sightline consisting of deep multiband imaging and further VLT spectroscopy. By fitting stellar population synthesis models to the photometric Spectral Energy Distribution we constrain the physical properties of the z = 2.583 DLA galaxy, and we infer its morphology by fitting a Sérsic model to its surface brightness profile. We find it to be a relatively massive (M
1010 M), strongly star-forming (SFR 30 M yr−1), dusty (E(B − V) = 0.4) galaxy with a disc-like morphology. We detect strong emission lines from the z = 2.583 DLA (O ii λ3727, O iii λλ4960, 5007, Hβ and Hα, albeit at low signal-to-noise ratio except for the O iii λ5007 line). The metallicity derived from the emission lines is consistent with the absorption metallicity (12 + log (O/H) = 8.8 ± 0.2). We also detect O iii λ5007 emission from the galaxy counterpart of the z = 2.412 DLA at a small impact parameter (<2 kpc). Overall our findings are consistent with the emerging picture that high-metallicity DLAs are associated with relatively luminous and massive galaxy counterparts, compared to typical DLAs.
We present adaptive optics imaging of the core-collapse supernova (SN) 2009md, which we use together with archival Hubble Space Telescope data to identify a coincident progenitor candidate. We find ...the progenitor to have an absolute magnitude of V=−4.63+0.3
−0.4 mag and a colour of V−I= 2.29+0.25
−0.39 mag, corresponding to a progenitor luminosity of log L/L⊙∼ 4.54 ± 0.19 dex. Using the stellar evolution code STARS, we find this to be consistent with a red supergiant progenitor with M= 8.5+6.5
−1.5 M⊙. The photometric and spectroscopic evolution of SN 2009md is similar to that of the class of sub-luminous Type IIP SNe; in this paper we compare the evolution of SN 2009md primarily to that of the sub-luminous SN 2005cs. We estimate the mass of 56Ni ejected in the explosion to be (5.4 ± 1.3) × 10−3 M⊙ from the luminosity on the radioactive tail, which is in agreement with the low 56Ni masses estimated for other sub-luminous Type IIP SNe. From the light curve and spectra, we show the SN explosion had a lower energy and ejecta mass than the normal Type IIP SN 1999em. We discuss problems with stellar evolutionary models, and the discrepancy between low observed progenitor luminosities (log L/L⊙∼4.3-5 dex) and model luminosities after the second dredge-up for stars in this mass range, and consider an enhanced carbon burning rate as a possible solution. In conclusion, SN 2009md is a faint SN arising from the collapse of a progenitor close to the lower mass limit for core collapse. This is now the third discovery of a low-mass progenitor star producing a low-energy explosion and low 56Ni ejected mass, which indicates that such events arise from the lowest end of the mass range that produces a core-collapse SN (7-8 M⊙).
We present early photometric and spectroscopic observations of SN 2013ej, a bright Type IIP supernova (SN) in M74. SN 2013ej is one of the closest SNe ever discovered. The available archive images ...and the early discovery help to constrain the nature of its progenitor. The earliest detection of this explosion was on 2013 July 24.125 ut and our spectroscopic monitoring with the FLOYDS spectrographs began on July 27.7 ut, continuing almost daily for two weeks. Daily optical photometric monitoring was achieved with the 1 m telescopes of the Las Cumbres Observatory Global Telescope (LCOGT) network, and was complemented by UV data from Swift and near-infrared spectra from Public ESO Spectroscopic Survey of Transient Objects and Infrared Telescope Facility. The data from our monitoring campaign show that SN 2013ej experienced a 10 d rise before entering into a well-defined plateau phase. This unusually long rise time for a Type IIP has been seen previously in SN 2006bp and SN 2009bw. A relatively rare strong absorption blueward of Hα is present since our earliest spectrum. We identify this feature as Si ii, rather than high-velocity Hα as sometimes reported in the literature.
ABSTRACT We present late-time observations of the site of the Type Ibn supernova (SN) 2006jc, acquired with the Hubble Space Telescope Advanced Camera for Surveys. A faint blue source is recovered at ...the SN position, with brightness , and mag, although there is no detection in a contemporaneous narrow-band image. The spectral energy distribution of the late-time source is well-fit by a stellar-like spectrum ( and ), subject to only a small degree of reddening-consistent with that estimated for SN 2006jc itself at early-times. The lack of further outbursts after the explosion of SN 2006jc suggests that the precursor outburst originated from the progenitor. The possibility of the source being a compact host cluster is ruled out on the basis of the source's faintness; however, the possibility that the late-time source may be an unresolved light echo originating in a shell or sphere of pre-SN dust (within a radius ) is also discussed. Irrespective of the nature of the late-time source, these observations rule out a luminous blue variable as a companion to the progenitor of SN 2006jc.
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