It is difficult to establish the properties of massive stars that explode as supernovae. The electromagnetic emission during the first minutes to hours after the emergence of the shock from the ...stellar surface conveys important information about the final evolution and structure of the exploding star. However, the unpredictable nature of supernova events hinders the detection of this brief initial phase. Here we report the serendipitous discovery of a newly born, normal type IIb supernova (SN 2016gkg), which reveals a rapid brightening at optical wavelengths of about 40 magnitudes per day. The very frequent sampling of the observations allowed us to study in detail the outermost structure of the progenitor of the supernova and the physics of the emergence of the shock. We develop hydrodynamical models of the explosion that naturally account for the complete evolution of the supernova over distinct phases regulated by different physical processes. This result suggests that it is appropriate to decouple the treatment of the shock propagation from the unknown mechanism that triggers the explosion.
Context.
The progenitor and explosion properties of type II supernovae (SNe II) are fundamental to understanding the evolution of massive stars. Particular attention has been paid to the initial ...masses of their progenitors, but despite the efforts made, the range of initial masses is still uncertain. Direct imaging of progenitors in pre-explosion archival images suggests an upper initial mass cutoff of ∼18
M
⊙
. However, this is in tension with previous studies in which progenitor masses inferred by light-curve modelling tend to favour high-mass solutions. Moreover, it has been argued that light-curve modelling alone cannot provide a unique solution for the progenitor and explosion properties of SNe II.
Aims.
We develop a robust method which helps us to constrain the physical parameters of SNe II by simultaneously fitting their bolometric light curve and the evolution of the photospheric velocity to hydrodynamical models using statistical inference techniques.
Methods.
We created pre-supernova red supergiant models using the stellar evolution code MESA, varying the initial progenitor mass. We then processed the explosion of these progenitors through hydrodynamical simulations, where we changed the explosion energy and the synthesised nickel mass together with its spatial distribution within the ejecta. We compared the results to observations using Markov chain Monte Carlo methods.
Results.
We apply this method to a well-studied set of SNe with an observed progenitor in pre-explosion images and compare with results in the literature. Progenitor mass constraints are found to be consistent between our results and those derived by pre-SN imaging and the analysis of late-time spectral modelling.
Conclusions.
We have developed a robust method to infer progenitor and explosion properties of SN II progenitors which is consistent with other methods in the literature. Our results show that hydrodynamical modelling can be used to accurately constrain the physical properties of SNe II. This study is the starting point for a further analysis of a large sample of hydrogen-rich SNe.
Type Ia supernovae form an observationally uniform class of stellar explosions, in that more luminous objects have smaller decline-rates. This one-parameter behaviour allows type Ia supernovae to be ...calibrated as cosmological 'standard candles', and led to the discovery of an accelerating Universe. Recent investigations, however, have revealed that the true nature of type Ia supernovae is more complicated. Theoretically, it has been suggested that the initial thermonuclear sparks are ignited at an offset from the centre of the white-dwarf progenitor, possibly as a result of convection before the explosion. Observationally, the diversity seen in the spectral evolution of type Ia supernovae beyond the luminosity-decline-rate relation is an unresolved issue. Here we report that the spectral diversity is a consequence of random directions from which an asymmetric explosion is viewed. Our findings suggest that the spectral evolution diversity is no longer a concern when using type Ia supernovae as cosmological standard candles. Furthermore, this indicates that ignition at an offset from the centre is a generic feature of type Ia supernovae.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
ABSTRACT
Type II supernovae (SNe II) show strong hydrogen features in their spectra throughout their whole evolution, while type IIb supernovae (SNe IIb) spectra evolve from dominant hydrogen lines ...at early times to increasingly strong helium features later on. However, it is currently unclear whether the progenitors of these SN types form a continuum in pre-SN hydrogen mass or whether they are physically distinct. SN light-curve morphology directly relates to progenitor and explosion properties such as the amount of hydrogen in the envelope, the pre-SN radius, the explosion energy, and the synthesized mass of radioactive material. In this work, we study the morphology of the optical-wavelength light curves of hydrogen-rich SNe II and hydrogen-poor SNe IIb to test whether an observational continuum exists between the two. Using a sample of 95 SNe (73 SNe II and 22 SNe IIb), we define a range of key observational parameters and present a comparative analysis between both types. We find a lack of events that bridge the observed properties of SNe II and IIb. Light-curve parameters such as rise times and post-maximum decline rates and curvatures clearly separate both SN types and we therefore conclude that there is no continuum, with the two SN types forming two observationally distinct families. In the V band a rise time of 17 d (SNe II lower and SNe IIb higher), and a magnitude difference between 30 and 40 d post-explosion of 0.4 mag (SNe II lower and SNe IIb higher) serve as approximate thresholds to differentiate both types.
Abstract We present a method of extrapolating the spectroscopic behavior of Type Ia supernovae (SNe Ia) in the near-infrared (NIR) wavelength regime up to 2.30 μ m using optical spectroscopy. Such a ...process is useful for accurately estimating K-corrections and other photometric quantities of SNe Ia in the NIR. A principal component analysis is performed on data consisting of Carnegie Supernova Project I & II optical and NIR FIRE spectra to produce models capable of making these extrapolations. This method differs from previous spectral template methods by not parameterizing models strictly by photometric light-curve properties of SNe Ia, allowing for more flexibility of the resulting extrapolated NIR flux. A difference of around −3.1% to −2.7% in the total integrated NIR flux between these extrapolations and the observations is seen here for most test cases including Branch core-normal and shallow-silicon subtypes. However, larger deviations from the observation are found for other tests, likely due to the limited high-velocity and broad-line SNe Ia in the training sample. Maximum-light principal components are shown to allow for spectroscopic predictions of the color-stretch light-curve parameter, s BV , within approximately ±0.1 units of the value measured with photometry. We also show these results compare well with NIR templates, although in most cases the templates are marginally more fitting to observations, illustrating a need for more concurrent optical+NIR spectroscopic observations to truly understand the diversity of SNe Ia in the NIR.
Abstract
Supernova (SN) 2021ocs was discovered in the galaxy NGC 7828 (
z
= 0.01911) within the interacting system Arp 144 and subsequently classified as a normal Type Ic SN around peak brightness. ...Very Large Telescope/FORS2 observations in the nebular phase at 148 days reveal that the spectrum is dominated by oxygen and magnesium emission lines of different transitions and ionization states: O
i
, O
i
, O
ii
, O
iii
, Mg
i
, and Mg
ii
. Such a spectrum has no counterpart in the literature, though it bears a few features similar to those of some interacting Type Ibn and Icn SNe. Additionally, SN 2021ocs showed a blue color, (
g
−
r
) ≲ −0.5 mag, after the peak and up to late phases, atypical for a Type Ic SN. Together with the nebular spectrum, this suggests that SN 2021ocs underwent late-time interaction with an H/He-poor circumstellar medium (CSM) resulting from the pre-SN progenitor mass loss during its final ∼1000 days. The strong O and Mg lines and the absence of strong C and He lines suggest that the progenitor star’s O–Mg layer is exposed, which places SN 2021ocs as the most extreme case of a massive progenitor star’s envelope stripping in interacting SNe, followed by Type Icn (stripped C–O layer) and Ibn (stripped He-rich layer) SNe. This is the first time such a case is reported in the literature. The SN 2021ocs emphasizes the importance of late-time spectroscopy of SNe, even for those classified as normal events, to reveal the inner ejecta and progenitor star’s CSM and mass loss.
Aims. The observational diversity displayed by various Type IIn supernovae (SNe IIn) is explored and quantified. In doing so, a more coherent picture ascribing the variety of observed SNe IIn types ...to particular progenitor scenarios is sought. Methods. Carnegie Supernova Project (CSP) optical and near-infrared light curves and visual-wavelength spectroscopy of the Type IIn SNe 2005kj, 2006aa, 2006bo, 2006qq, and 2008fq are presented. Combined with previously published observations of the Type IIn SNe 2005ip and 2006jd, the full CSP sample is used to derive physical parameters that describe the nature of the interaction between the expanding SN ejecta and the circumstellar material (CSM). Results. For each SN of our sample, we find counterparts, identifying objects similar to SNe 1994W (SN 2006bo), 1998S (SN 2008fq), and 1988Z (SN 2006qq). We present the unprecedented initial u-band plateau of SN 2006aa, and its peculiar late-time luminosity and temperature evolution. For each SN, mass-loss rates of 10-4−10-2M⊙ yr-1 are derived, assuming the CSM was formed by steady winds. Typically wind velocities of a few hundred km s-1 are also computed. Conclusions. The CSP SN IIn sample seems to be divided into subcategories rather than to have exhibited a continuum of observational properties. The wind and mass-loss parameters would favor a luminous blue variable progenitor scenario. However, the assumptions made to derive those parameters strongly influence the results, and therefore, other progenitor channels behind SNe IIn cannot be excluded at this time.
We present an analysis of ultraviolet (UV) to near-infrared observations of the fast-declining Type Ia supernovae (SNe Ia) 2007on and 2011iv, hosted by the Fornax cluster member NGC 1404. The B-band ...light curves of SN 2007on and SN 2011iv are characterised by Δm15 (B) decline-rate values of 1.96 mag and 1.77 mag, respectively. Although they have similar decline rates, their peak B- and H-band magnitudes differ by ~ 0.60 mag and ~0.35 mag, respectively. After correcting for the luminosity vs. decline rate and the luminosity vs. colour relations, the peak B-band and H-band light curves provide distances that differ by ~ 14% and ~ 9%, respectively. These findings serve as a cautionary tale for the use of transitional SNe Ia located in early-type hosts in the quest to measure cosmological parameters. Interestingly, even though SN 2011iv is brighter and bluer at early times, by three weeks past maximum and extending over several months, its B − V colour is 0.12 mag redder than that of SN 2007on. To reconcile this unusual behaviour, we turn to guidance from a suite of spherical one-dimensional Chandrasekhar-mass delayed-detonation explosion models. In this context, 56Ni production depends on both the so-called transition density and the central density of the progenitor white dwarf. To first order, the transition density drives the luminosity–width relation, while the central density is an important second-order parameter. Within this context, the differences in the B − V colour evolution along the Lira regime suggest that the progenitor of SN 2011iv had a higher central density than SN 2007on.
Abstract
The coming era of large photometric wide-field surveys will increase the detection rate of supernovae by orders of magnitude. Such numbers will restrict spectroscopic follow-up in the vast ...majority of cases, and hence new methods based solely on photometric data must be developed. Here, we construct a complete Hubble diagram of Type II supernovae (SNe II) combining data from three different samples: the Carnegie Supernova Project-I, the Sloan Digital Sky Survey II SN, and the Supernova Legacy Survey. Applying the Photometric Color Method (PCM) to 73 SNe II with a redshift range of 0.01–0.5 and with no spectral information, we derive an intrinsic dispersion of 0.35 mag. A comparison with the Standard Candle Method (SCM) using 61 SNe II is also performed and an intrinsic dispersion in the Hubble diagram of 0.27 mag, i.e., 13% in distance uncertainties, is derived. Due to the lack of good statistics at higher redshifts for both methods, only weak constraints on the cosmological parameters are obtained. However, assuming a flat universe and using the PCM, we derive the universe’s matter density:
providing a new independent evidence for dark energy at the level of two sigma.
We present new data for five underluminous Type II-plateau supernovae (SNe IIP), namely SN 1999gn, SN 2002gd, SN 2003Z, SN 2004eg and SN 2006ov. This new sample of low-luminosity SNe IIP (LL SNe IIP) ...is analysed together with similar objects studied in the past. All of them show a flat light-curve plateau lasting about 100 d, an underluminous late-time exponential tail, intrinsic colours that are unusually red, and spectra showing prominent and narrow P Cygni lines. A velocity of the ejected material below 103 km s−1 is inferred from measurements at the end of the plateau. The 56Ni masses ejected in the explosion are very small (≤10−2 M). We investigate the correlations among 56Ni mass, expansion velocity of the ejecta and absolute magnitude in the middle of the plateau, confirming the main findings of Hamuy, according to which events showing brighter plateau and larger expansion velocities are expected to produce more 56Ni. We propose that these faint objects represent the LL tail of a continuous distribution in parameters space of SNe IIP. The physical properties of the progenitors at the explosion are estimated through the hydrodynamical modelling of the observables for two representative events of this class, namely SN 2005cs and SN 2008in. We find that the majority of LL SNe IIP, and quite possibly all, originate in the core collapse of intermediate-mass stars, in the mass range 10-15 M.
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