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Register a new userThe aspherical explosion of the Type IIP SN 2017gmr
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Type IIP supernovae (SNe IIP), which represent the most common class of core-collapse (CC) SNe, show a rapid increase in continuum polarization just after entering the tail phase. This feature can be explained by a highly asymmetric helium core, which is exposed when the hydrogen envelope becomes transparent. Here we report the case of a SN IIP (SN~2017gmr) that shows an unusually early rise of the polarization, $gtrsim 30$ days before the start of the tail phase. This implies that SN~2017gmr is an SN IIP that has very extended asphericity. The asymmetries are not confined to the helium core, but reach out to a significant part of the outer hydrogen envelope, hence clearly indicating a marked intrinsic diversity in the aspherical structure of CC explosions. These observations provide new constraints on the explosion mechanism, where viable models must be able to produce such extended deviations from spherical symmetry, and account for the observed geometrical diversity.
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The unusual Type IIP SN 2017gmr is revisited in order to pinpoint the origin of its anomalous features, including the peculiar light curve after about 100 days. The hydrodynamic modelling suggests the enormous explosion energy of about 10^52 erg. We find that the light curve with the prolonged plateau/tail transition can be reproduced either in the model with a high hydrogen abundance in the inner ejecta and a large amount of radioactive Ni-56, or in the model with an additional central energy source associated with the fallback/magnetar interaction in the propeller regime. The asymmetry of the late H-alpha emission and the reported linear polarization are reproduced by the model of the bipolar Ni-56 ejecta. The similar bipolar structure of the oxygen distribution is responsible for the two-horn structure of the [O I] 6360, 6364 A emission. The bipolar Ni-56 structure along with the high explosion energy are indicative of the magneto-rotational explosion. We identify narrow high-velocity absorption features in H-alpha and He I 10830 A lines with their origin in the fragmented cold dense shell formed due to the outer ejecta deceleration in a confined circumstellar shell.
The enigmatic type IIP SN 2016X demonstrates the unprecedented asphericity in the nebular H-alpha line profile, the absence of nebular [O I] emission, and the unusual occultation effect due to the internal dust. The hydrodynamic modelling of the bolometric light curve and expansion velocities suggests that the event is an outcome of the massive star explosion that ejected 28 Msun with the kinetic energy of 1.7x10^51 erg and 0.03 Msun of radioactive Ni-56. We recover the bipolar distribution of Ni-56 from the H-alpha profile via the simulation of the emissivity produced by non-spherical Ni-56 ejecta. The conspicuous effect of the dust absorption in the H-alpha profile rules out the occultation by the dusty sphere or dusty thick disk but turns out consistent with the thin dusty disk-like structure in the plane perpendicular to the bipolar axis. We speculate that the absence of the nebular [O I] emission might originate from the significant cooling of the oxygen-rich matter mediated by CO and SiO molecules.
We present observations and analysis of SN 2020cxd, a Low luminous (LL), long-lived Type IIP SN. This object was a clear outlier in the magnitude-limited SN sample recently presented by the ZTF Bright Transient Survey. We demonstrate that SN 2020cxd is an additional member of the group of LL SNe, and discuss the rarity of LL SNe in the context of the ZTF survey, and how further studies of these faintest members of the CC SN family might help understand the underlying initial mass function for stars that explode.
We present high-cadence ultraviolet (UV), optical, and near-infrared (NIR) data on the luminous Type II-P supernova SN 2017gmr from hours after discovery through the first 180 days. SN 2017gmr does not show signs of narrow, high-ionization emission lines in the early optical spectra, yet the optical lightcurve evolution suggests that an extra energy source from circumstellar medium (CSM) interaction must be present for at least 2 days after explosion. Modeling of the early lightcurve indicates a ~500R$_{odot}$ progenitor radius, consistent with a rather compact red supergiant, and late-time luminosities indicate up to 0.130 $pm$ 0.026 M$_{odot}$ of $^{56}$Ni are present, if the lightcurve is solely powered by radioactive decay, although the $^{56}$Ni mass may be lower if CSM interaction contributes to the post-plateau luminosity. Prominent multi-peaked emission lines of H$alpha$ and [O I] emerge after day 154, as a result of either an asymmetric explosion or asymmetries in the CSM. The lack of narrow lines within the first two days of explosion in the likely presence of CSM interaction may be an example of close, dense, asymmetric CSM that is quickly enveloped by the spherical supernova ejecta.
The recent study of SN 2013fs flash spectrum suggests enormous for SN IIP explosion energy, far beyond possibilities of the neutrino mechanism. The issue of the explosion energy of SN 2013fs is revisited making use of effects of the early supernova interaction with the dense circumstellar shell. The velocity of the cold dense shell between reverse and forward shocks is inferred from the analysis of the broad heii,4686,AA on day 2.4. This velocity alongside with other observables provide us with an alternative energy estimate of $sim1.8times10^{51}$,erg for the preferred mass of $sim10$msun. The inferred value is within the range of the neutrino driven explosion.
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