[Paper Review] Formation of Fast-spinning Neutron Stars in Close Binaries and Magnetar-driven Stripped-envelope Supernovae

Rui-Chong Hu, Jin-Ping Zhu+9 more|arXiv (Cornell University)|Jan 16, 2023

Gamma-ray bursts and supernovae7 citations

TL;DR

The paper demonstrates that tidal spin-up of helium stars in close binaries via common-envelope and stable mass transfer channels can form fast-spinning magnetars at core collapse, reproducing the observed energy–ejecta mass correlation and matching magnetar-driven SESNe rate densities across metallicities.

ABSTRACT

Extreme stripped-envelope supernovae (SESNe), including Type Ic superluminous supernovae (SLSNe-I), broad-line Type Ic SNe (SNe Ic-BL), and fast blue optical transients (FBOTs), are widely believed to harbor a newborn fast-spinning highly-magnetized neutron star (``magnetar''), which can lose its rotational energy via spin-down processes to accelerate and heat the ejecta. The progenitor(s) of these magnetar-driven SESNe, and the origin of considerable angular momentum (AM) in the cores of massive stars to finally produce such fast-spinning magnetars upon core-collapse are still under debate. Popular proposed scenarios in the literature cannot simultaneously explain their event rate density, SN and magnetar parameters, and the observed metallicity. Here, we perform a detailed binary evolution simulation that demonstrates that tidal spin-up helium stars with efficient AM transport mechanism in close binaries can form fast-spinning magnetars at the end of stars' life to naturally reproduce the universal energy-mass correlation of these magnetar-driven SESNe. Our models are consistent with the event rate densities, host environments, ejecta masses, and energetics of these different kinds of magnetar-driven SESNe, supporting that the isolated common-envelope formation channel could be a major common origin of magnetar-driven SESNe. The remnant compact binary systems of magnetar-driven SESNe are progenitors of some gravitational-wave transients and galactic systems.

Motivation & Objective

• Motivate and explain the need to understand how magnetar-driven SESNe form and why their angular momentum is so high.
• Show that tidal spin-up in close binaries can produce fast-spinning magnetars at core collapse across sub-solar to super-solar metallicities.
• Reproduce the universal initial magnetar energy–ejecta mass correlation observed for SLSNe, GRB-SNe, SNe Ic-BL, and FBOTs.
• Demonstrate that the isolated common-envelope (CEE) and stable mass transfer (SMT) channels can account for event rate densities and host environments of magnetar-driven SESNe.

Proposed method

• Perform detailed binary evolution simulations with the MESA code for helium stars in close binaries undergoing tides and AM transport.
• Adopt diffusive rotational mixing and angular momentum transport including the Tayler–Spruit dynamo (with its revised version for comparison).
• Compute initial magnetar rotational energy from core-collapse via AM conservation and an empirical M_CO–M_NS,b relation, deriving ejecta masses M_ej.
• Carry out binary population synthesis with the BSE code to estimate redshift-dependent event rate densities for SLSNe, lGRBs, SNe Ic-BL, and FBOTs across metallicities.
• Assemble observational data of magnetar-driven SESNe (P_rot,i, M_ej) and compare with simulated E_rot,i–M_ej relations across metallicities.
• Estimate likely companion types at explosion and assess the fate of remnants and potential gravitational-wave sources.

Experimental results

Research questions

• RQ1 Can tidal spin-up in close binaries via CEE/SMT channels produce the required fast-spinning magnetars for magnetar-driven SESNe across a range of metallicities?
• RQ2 Does the model reproduce the observed universal E_rot,i–M_ej correlation linking SLSNe, GRB-SNe, SNe Ic-BL, and FBOTs?
• RQ3 What is the predicted redshift-dependent rate density of magnetar-driven SESNe and how does it compare with observations across metallicity environments?
• RQ4 What are the likely binary configurations and companion types at the time of explosion, and what are the implications for remnants and gravitational-wave sources?
• RQ5 To what extent do metallicity and AM transport efficiency control the formation of fast magnetars and the suppression or enhancement of magnetar-driven SESNe?

Key findings

• Simulations show that helium stars (M_He,i ~ 5–40 M_sun) in close binaries (P_orb,i ≲ 1–2 days) can achieve fast magnetar rotation consistent with observed E_rot,i–M_ej correlations.
• In sub-solar to solar metallicities, most SLSNe, GRB-SNe, and SNe Ic-BL can be produced via tidal spin-up in close binaries, aligning with observed host metallicities and ejecta masses.
• FBOTs are explained by lower-mass helium stars (M_He,i ≲ 5 M_sun) in binaries, potentially with P_orb,i ≲ 10 days, and can originate even in wider binaries with sufficient remnant energy.
• At super-solar metallicities, stronger winds reduce available angular momentum, suppressing magnetar-driven SESNe and favoring ordinary SNe Ic outcomes.
• Binary population synthesis predicts SLSN and lGRB rate densities comparable to observations when metallicity and beaming are accounted for, and FBOT rate density near observational estimates (~1% of CC SN).
• Most magnetar-driven SESNe arise from the first-formed tidally spun-up helium star in a close binary with an MS companion, with CEE as a major formation channel and significant implications for surviving NS binaries.