Work

Circumbinary discs as the origin of circumstellar material around interacting H-poor supernovae and fast blue optical transients

Year: 2026

Type: article

Abstract: Around 10% of hydrogen-poor supernovae (SNe) explode inside compact (∼ 10^ 15 cm), massive (∼ 0.1 M_⊙ ) circumstellar material (CSM), signalling an episode of enhanced pre-explosion mass loss whose mechanism remains unclear. The extreme members of this population are considered to constitute some of the fast blue optical transients (FBOTs), which exhibit rapid rise times of a few days and high peak luminosities of ∼ 10^ 44 erg . Recent binary evolution calculations show that the expansion of helium stars during their latest evolutionary stages can trigger a rapid but stable mass-transfer episode that reaches a rate of ∼ 10^ -4 M _⊙ yr^ -1 and is sustained for ∼ 10 kyr before the explosion. It has been suggested that if this mass transfer is non-conservative and the lost mass remains gravitationally bound to the binary, it can form a dense circumbinary disc (CBD) that could explain the observed dense CSM. However, a detailed, quantitative analysis of this process and the resulting CBD properties such as its mass, radius, and density profile, which are required for light curve calculations and event rate estimates, has not yet been undertaken. We present a set of models that solve the viscous evolution of such a CBD subjected to time-dependent mass injection. This framework self-consistently includes the angular momentum exchange between the central binary and the CBD. We find that although the injected mass is initially sub-Keplerian, a lower `accretion eigenvalue' (̧hi, corresponding to the binary torquing the CBD) prevents more mass from falling back onto the central binary. For our fiducial set of models with ̧hi = -1 and a viscosity parameter of α = 0.01, the CBD immediately prior to the explosion reaches a mass of 0.07-0.20 M _⊙, a half-mass radius of 640 - 4000 R _⊙, and an aspect ratio of þeta = H/R ∼ 0.1. We also show that the final CBD mass is primarily determined by ̧hi, which governs how much of the injected mass is retained within the CBD, whereas the half-mass radius is primarily determined by α, as it controls the extent of viscous spreading. Finally, by calculating the evolution of interaction luminosity from a SN explosion inside the CBD, we show that the interaction between SN ejecta and the CBD can power some of the fastest-evolving interacting Type Ibc SNe that can be classified as FBOTs, such as SN 2018gep and SN 2019jc. Despite uncertainties in the model parameters, our results demonstrate that CBD formation triggered by rapid, stable mass transfer is a viable mechanism to explain the dense circumstellar environments observed around rapid, hydrogen-poor interacting SNe. To further investigate this CSM formation channel, a more detailed understanding of CBD--binary interaction is warranted.

Source: Astronomy and Astrophysics

DOI: 10.1051/0004-6361/202660538

Authors: Ryotaro Chiba, Semih Tuna, Brian D. Metzger, Takashi J. Moriya

Language: English

Topic: Gamma-ray bursts and supernovae

Subfield: Astronomy and Astrophysics

Field: Physics and Astronomy

Domain: Physical Sciences

Open Access status: gold

Estimated APC paid: $1,865