Bare collapse, formation of neutron star binaries and fast optical transients

Abstract

‘Bare collapse’, the collapse of a bare stellar core to a neutron star with a very small mass ejection links two seemingly unrelated phenomena: the formation of binary neutron star (BNS) systems and the observations of fast and luminous optical transients. We carried out calculations of the collapse due to electron-capture of both evolutionary and synthetic isentropic bare stellar cores. We find that the collapse results in the formation of a light ∼1.3M⊙ neutron star and an ejection of ∼0.1M⊙ at ∼0.1c. The outer shell of the ejecta is composed of 56Ni that can power an ultra-stripped supernova. The models we explored can explain most of the observed fast optical flares but not the brightest ones. Collapse of cores surrounded by somewhat more massive envelopes can produce larger amounts of 56Ni and explain brighter flares. Alternatively, those events can arise due to interaction of the very energetic ejecta with winds that were ejected from the progenitor a few days before the collapse.

Late-time Hubble Space Telescope Observations of AT 2018cow. II. Evolution of a UV-bright Underlying Source 2–4 Yr Post-discovery

“…Over the past decade, a class of peculiar transients has been discovered with brightness similar to supernovae (SNe), but a much shorter timescale, often accompanied by persistent blue color, commonly termed Fast Blue Optical Transients (FBOTs; e.g., Drout et al 2014;Arcavi et al 2016;Tanaka et al 2016;Pursiainen et al 2018;Rest et al 2018;Tampo et al 2020;Wiseman et al 2020;Ho et al 2023). The much shorter timescale is incompatible with standard SN models powered by radioactive decay and hydrogen recombination (which serve to prolong light curves), and thus alternative models were proposed, most commonly involving power sources such as interaction between ejecta and circumstellar material (CSM; Ofek et al 2010;Shivvers et al 2016;Kleiser et al 2018;McDowell et al 2018;Rest et al 2018;Tolstov et al 2019;Wang et al 2019;Suzuki et al 2020;Wang & Li 2020;Karamehmetoglu et al 2021;Maeda & Moriya 2022;Margalit et al 2022;Margalit 2022;Khatami & Kasen 2023;Liu et al 2023;Mor et al 2023) and energy injection by central engines such as neutron stars (NSs; Yu et al 2015;Hotokezaka et al 2017;Whitesides et al 2017;Liu et al 2022;Wang & Gan 2022) or black holes (BHs; Kashiyama & Quataert 2015;Rest et al 2018;Kawana et al 2020;Kremer et al 2021;Tsuna et al 2021;Fujibayashi et al 2022).…”

Late-time Hubble Space Telescope Observations of AT 2018cow. I. Further Constraints on the Fading Prompt Emission and Thermal Properties 50–60 days Post-discovery

“…As a result, a variety of alternative scenarios have been proposed to explain the characteristics of FBOTs, some of which involve interactions with circumstellar material (CSM; Ofek et al 2010;Shivvers et al 2016;Kleiser et al 2018b;McDowell et al 2018;Rest et al 2018;Tolstov et al 2019;Wang et al 2019;Suzuki et al 2020;Wang & Li 2020;Karamehmetoglu et al 2021;Maeda & Moriya 2022;Margalit et al 2022;Margalit 2022;Khatami & Kasen 2023;Liu et al 2023;Mor et al 2023), energy injection by a central engine such as a neutron star (NS; Yu et al 2015;Hotokezaka et al 2017;Whitesides et al 2017;Liu et al 2022;Wang & Gan 2022) or a black hole (BH; Kashiyama & Quataert 2015;Rest et al 2018;Tsuna et al 2021;Fujibayashi et al 2022), tidal disruption events (TDEs; Kawana et al 2020;Kremer et al 2021), electron-capture supernovae (ECSNe; Moriya & Eldridge 2016), and SNe within extended envelopes (Brooks et al 2017;Kleiser et al 2018a).…”

Inhomogeneous Enrichment of Radioactive Nuclei in the Galaxy: Deposition of Live 53Mn, 60Fe, 182Hf, and 244Pu into Deep-sea Archives. Surfing the Wave?

“…CCSNe mostly occur asymmetrically, resulting in a natal kick for the newly born NS, which could lead to offsets in the NSM locations from the original CCSNe that formed the two NSs (e.g., van de Voort et al 2022). However, various studies (e.g., Beniamini & Piran 2016;Tauris et al 2017) have shown that the second born NS in the majority of NS binaries in our Galaxy were formed by much weaker explosions (possibly ultrastripped SNe; see Tauris et al 2015;Mor et al 2023) that resulted in very weak kicks. Indeed, Perets & Beniamini (2021) showed that the offset locations of short GRBs-when divided according to galaxy type-support the idea that kicks play a subdominant role in setting binary NS merger offsets.…”