We present photometric and spectroscopic observations of the type Ibn supernova (SN) 2019uo, the second ever SN Ibn with flash ionization (He II, C III, N III) features in its early spectra. SN 2019uo displays a rapid post-peak luminosity decline of 0.1 mag d −1 similar to most of the SNe Ibn, but is fainter (M V max = −18.30 ± 0.24 mag) than a typical SN Ibn and shows a color evolution that places it between SNe Ib and the most extreme SNe Ibn. SN 2019uo shows P-cygni He I features in the early spectra which gradually evolves and becomes emission dominated post peak. It also shows faster evolution in line velocities as compared to most other members of the type Ibn subclass. The bolometric light curve is fairly described by a 56 Ni + circumstellar interaction model.

The gamma-ray burst GRB 211211A and its associated kilonova-like emission were reported recently. A significant difference between this association event and GRB 170817A/AT 2017gfo is that GRB 211211A has a very long duration. In this Letter, we show that this association event may arise from a neutron star–white dwarf (NS–WD) merger if the central engine leaves a magnetar behind. Within the NS–WD merger, the main burst of GRB 211211A could be produced by magnetic bubble eruptions from toroidal magnetic field amplification of the premerger NS. This toroidal field amplification can be induced by the runaway accretion from the WD debris disk if the disk is in low initial entropy and efficient wind, while the extended emission of GRB 211211A is likely involved with magnetic propelling. The observed energetics and duration of the prompt emission of GRB 211211A can be fulfilled in comparison with those of accretion in a hydrodynamical thermonuclear simulation, as long as the WD has a mass ≳1M ⊙. Moreover, if the X-ray plateau in GRB afterglows is due to the magnetar spin-down radiation, GRB optical afterglows and kilonova-like emission can be jointly well modeled combining the standard forward shock with the radioactive decay power of 56Ni adding a rotational power input from the postmerger magnetar.

It is still a highly debated question as to whether fast radio bursts (FRBs) are classified into one or two populations. To probe this question, we perform a statistical analysis using the first Canadian Hydrogen Intensity Mapping Experiment Fast Radio Burst (CHIME/FRB) catalog and identify a few discriminant properties between repeating and non-repeating FRBs such as the repetition rate, duration, bandwidth, spectral index, peak luminosity, and potential peak frequency. If repeating and non-repeating FRBs belong to one population, their distribution distinctions for the repetition rate and duration can be explained by the selection effect due to the beamed emission as in Connor et al. However, we obtain that the distribution distinctions for the spectral index and potentially the peak frequency cannot be explained by the beamed emission within the framework of either the coherent curvature radiation or synchrotron maser emission. This indicates that there could be two populations. We further discuss three possible scenarios for the required two populations.

PS15dpn is a luminous rapidly rising Type Ibn supernova (SN) discovered by Pan-STARRS1. Previous study has showed that its bolometric light curve (LC) cannot be explained by the 56Ni model. In this paper, we used the 56Ni model, the magnetar model, the circumstellar interaction (CSI) model, and the CSI plus 56Ni model to fit the bolometric LC of PS15dpn. We found that the 56Ni model can fit the bolometric LC but the parameters are unrealistic, and that the magnetar model, the CSI model, and the CSI plus 56Ni model can match the data with reasonable parameters. Considering the fact that the emission lines indicative of the interaction between the ejecta and the circumstellar medium (CSM) have been confirmed, and that the SNe produced by the explosions of massive stars can synthesize moderate amounts of 56Ni, we suggest that the CSI plus 56Ni model is the most promising model. Assuming that the CSM is a shell (wind), the masses of the ejecta, the CSM, and the 56Ni are ( M ⊙), M ⊙ ( M ⊙), and M ⊙ ( M ⊙), respectively. The inferred ejecta masses are consistent with the scenario that the progenitors of SNe Ibn are massive Wolf–Rayet stars. Adopting the shell CSM scenario, the shell might be expelled by an eruption of the progenitor just ∼17–167 days prior to the SN explosion; for the wind scenario, the inferred mass-loss rate of the wind is ∼8.0 M ⊙ yr−1, indicating that the wind is a “super-wind” having an extremely high mass-loss rate.