Authors affiliations can be found at the end of the text.Long duration gamma-ray bursts (GRBs) mark the birth of a compact object, a neutron star or black hole. At low-redshift (z < 0.2) these events are extremely rare and most are poorly known. Four nearby GRBs have been associated with Type Ic supernovae (SNe Ic), [1,2,3,4,5,6,7]. GRB/SNe lack hydrogen and helium, and are classified as SNe Ic, but have extremely broad features, which indicate the presence of material at very high velocities (> 0.3c) [8]. They have a kinetic energy (E k ) of ∼ > 10 52 erg, and are thought to be the explosion of bare carbon-oxygen cores of stars with initial mass 35-50 M [9]. Here we report observations of the nearby GRB 161219B (z = 0.1475, [10]) and the associated SN2016jca. We obtained a high-cadence time-series of spectra and photometry starting 2 days after explosion. The GRB afterglow had a late achromatic break 12 days after outburst which indicates that the relativistic material was ejected in an outflow with a large opening angle. We first identified the SN 5 days after the GRB [11]. Such an early detection gives us the opportunity to explore the outermost layers of the ejecta. We find the outer most ejecta are dominated by heavy elements, while lighter elements are present in high abundance at low velocities. Geometrically this suggests that we are viewing a high velocity nuclearly processed outflow down its axis. This and the wide opening angle suggests a highly magnetized millisecond pulsar may power the explosion.GRB 161219B exploded on 19-12-2016. Our HST image (Figure 1) shows that SN 2016jca is located in an edge-on spiral galaxy; an analysis of the host galaxy emission lines at the location of the transient, based on a VLT X-Shooter spectrum, indicates a metallicity range 0.3 < Z/Z < 0.55. This is characteristic of other low-redshift gamma-ray burst host galaxies [20,21,22,23].Ten spectra of the optical transient were obtained between 1.99 and 32.65 days (rest frame) after explosion. The first spectra are dominated by the afterglow, and at t = 5.52 d the SN is clearly visible. The spectral features are typical of previously observed Supplementary material can be found at https://www.astro.ljmu.ac.uk/ astcasha/SN2016jcasupplemantary.pdf arXiv:1702.04339v2 [astro-ph.HE]

The Type Ia supernova (SN Ia) LSQ14fmg exhibits exaggerated properties that may help to reveal the origin of the “super-Chandrasekhar” (or 03fg-like) group. The optical spectrum is typical of a 03fg-like SN Ia, but the light curves are unlike those of any SNe Ia observed. The light curves of LSQ14fmg rise extremely slowly. At −23 rest-frame days relative to B-band maximum, LSQ14fmg is already brighter than mag before host extinction correction. The observed color curves show a flat evolution from the earliest observation to approximately 1 week after maximum. The near-infrared light curves peak brighter than −20.5 mag in the J and H bands, far more luminous than any 03fg-like SNe Ia with near-infrared observations. At 1 month past maximum, the optical light curves decline rapidly. The early, slow rise and flat color evolution are interpreted to result from an additional excess flux from a power source other than the radioactive decay of the synthesized 56Ni. The excess flux matches the interaction with a typical superwind of an asymptotic giant branch (AGB) star in density structure, mass-loss rate, and duration. The rapid decline starting at around 1 month past B-band maximum may be an indication of rapid cooling by active carbon monoxide (CO) formation, which requires a low-temperature and high-density environment. These peculiarities point to an AGB progenitor near the end of its evolution and the core degenerate scenario as the likely explosion mechanism for LSQ14fmg.

We place statistical constraints on Type Ia supernova (SN Ia) progenitors using 227 nebular phase spectra of 111 SNe Ia. We find no evidence of stripped companion emission in any of the nebular phase spectra. Upper limits are placed on the amount of mass that could go undetected in each spectrum using recent hydrodynamic simulations. With these null detections, we place an observational 3σ upper limit on the fraction of SNe Ia that are produced through the classical H-rich non-degenerate companion scenario of < 5.5%. Additionally, we set a tentative 3σ upper limit on He star progenitor scenarios of < 6.4%, although further theoretical modelling is required. These limits refer to our most representative sample including normal, 91bg-like, 91Tlike, and "Super Chandrasekhar" SNe Ia but excluding SNe Iax and SNe Ia-CSM. As part of our analysis, we also derive a Nebular Phase Phillips Relation, which approximates the brightness of a SN Ia from 150 − 500 days after maximum using the peak magnitude and decline rate parameter ∆m 15 (B).

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The diversity of Type II supernovae (SNe II) is thought to be driven mainly by differences in their progenitor’s hydrogen-rich (H-rich) envelope mass, with SNe IIP having long plateaus (∼100 days) and the most massive H-rich envelopes. However, it is an ongoing mystery why SNe II with short plateaus (tens of days) are rarely seen. Here, we present optical/near-infrared photometric and spectroscopic observations of luminous Type II short-plateau SNe 2006Y, 2006ai, and 2016egz. Their plateaus of about 50–70 days and luminous optical peaks (≲−18.4 mag) indicate significant pre-explosion mass loss resulting in partially stripped H-rich envelopes and early circumstellar material (CSM) interaction. We compute a large grid of MESA+STELLA single-star progenitor and light-curve models with various progenitor zero-age main-sequence (ZAMS) masses, mass-loss efficiencies, explosion energies, 56Ni masses, and CSM densities. Our model grid shows a continuous population of SNe IIP–IIL–IIb-like light-curve morphology in descending order of H-rich envelope mass. With large 56Ni masses (≳0.05 M ⊙), short-plateau SNe II lie in a confined parameter space as a transitional class between SNe IIL and IIb. For SNe 2006Y, 2006ai, and 2016egz, our findings suggest high-mass red supergiant (RSG) progenitors (M ZAMS ≃ 18–22 M ⊙) with small H-rich envelope masses ( ) that have experienced enhanced mass loss ( ) for the last few decades before the explosion. If high-mass RSGs result in rare short-plateau SNe II, then these events might ease some of the apparent underrepresentation of higher-luminosity RSGs in observed SN II progenitor samples.