Shocked jets in CCSNe can power the zoo of fast blue optical transients

Abstract

Evidence is mounting that recent multi-wavelength detections of fast blue optical transients (FBOTs) in star-forming galaxies comprise a new class of transients, whose origin is yet to be understood. We show that hydrogen-rich collapsing stars that launch relativistic jets near the central engine can naturally explain the entire set of FBOT observables. The jet-star interaction forms a mildly-relativistic shocked jet (inner cocoon) component, which powers cooling emission that dominates the high velocity optical signal during the first few weeks, with a typical energy of ∼ 10 50 − 10 51 erg. During this time, the cocoon radial energy distribution implies that the optical lightcurve exhibits a fast decay of L ∝ ∼ t −2.4 . After a few weeks, when the velocity of the emitting shell is ∼ 0.01 c, the cocoon becomes transparent, and the cooling stellar envelope governs the emission. During this transition, discontinuities may emerge in the lightcurve and spectra, as have been observed in a few FBOTs, such as AT2018cow. The interaction between the cocoon forward shock and the dense circumstellar winds generates synchrotron selfabsorbed emission in the radio bands, featuring a steady rise on a month timescale. After a few months, if the jet successfully pierces the stellar envelope, it decelerates, enters the observer's line of sight, and powers the peak of the radio lightcurve, which rapidly decays thereafter. The jet (and the inner cocoon) become optically thin to X-rays ∼ day after the collapse, allowing X-ray photons to diffuse from the central engine that launched the jet to the observer. Cocoon cooling emission is expected at higher volumetric rates than gamma-ray bursts (GRBs) by a factor of a few, similar to FBOTs. We rule out uncollimated outflows, however both GRB jets and failed collimated jets are compatible with all observables.

A common envelope jets supernova (CEJSN) impostor scenario for fast blue optical transients

“…Early emission from the hot cocoon (Fig. 3) similar in some aspects to the hot-cocoon in the scenario of Gottlieb, Tchekhovskoy, & Margutti (2022). Late emission from the dense equatorial region similar in some aspects to that in the geometrical model of Margutti et al (2019).…”

“…Soker, Grichener, & Gilkis (2019) mentioned that several emission sources and properties as well as the dense equatorial CSM of the polar-CEJSN scenario are similar to the general picture that Margutti et al (2019) describe. Here I further note that some processes and properties that I describe here are also similar to some processes in the FBOT scenario that Gottlieb, Tchekhovskoy, & Margutti (2022) develop. There are, however, some basic differences between the scenarios, in particular that in the polar-CEJSN and impostor scenarios the NS is an old one, rather than a newly born NS or BH, and that in the polar CEJSN and polar CEJSN impostor scenarios the CSM contains two opposite lobes along the polar directions.…”

“…The two opposite openings (funnels) in the polar directions give this scenario the name 'polar CEJSN' (Soker, Grichener, & Gilkis 2019) or polar CEJSN impostor (present study). The funnels in the polar directions are another property that distinguishes the polar CEJSN scenario from the scenario that Gottlieb, Tchekhovskoy, & Margutti (2022) propose in which the jets strongly interact with the envelope. 2019) find that the central power source ("engine") of AT 2018cow should release a total energy of 10 50 − 10 51.5 erg over a characteristic timescale of ≈ 10 3 − 10 5 s. They also deduce that the ejecta mass is M ej 0.1 − 1M and that it contains hydrogen and helium, but a limited 56 Ni mass of M Ni < 0.04M .…”

“…respectively. This energy is about equal to the jets' energy in the scenario of Gottlieb, Tchekhovskoy, & Margutti (2022), but here the jets are mainly baryonic while Gottlieb, Tchekhovskoy, & Margutti (2022) consider relativistic jets.…”

“…The enigmatic AT 2018cow event (Prentice et al 2018) and similar FBOTs have promoted the development of several scenarios for AT 2018cow-like FBOTs (e.g., Liu et al 2018;Fox & Smith 2019;Kuin et al 2019;Lyutikov & Toonen 2019;Margutti et al 2019;Quataert, Lecoanet, & Coughlin 2019;Yu et al 2019;Leung et al 2020;Mohan, An, & Yang 2020;Piro & Lu 2020;Uno & Maeda 2020;Kremer et al 2021;Xiang et al 2021;Gottlieb, Tchekhovskoy, & Margutti 2022). In the present study I do not compare the different scenarios with each other but rather present the polar-CEJSN impostor channel (section 2) and its new ingredients (section 3).…”