[Paper Review] Models for Gamma-Ray Burst Progenitors and Central Engines

S. E. Woosley|arXiv (Cornell University)|May 20, 2011

Gamma-ray bursts and supernovae4 citations

TL;DR

This paper reviews models for long-soft gamma-ray burst (LSB) progenitors and central engines, focusing on massive stars (>40 M☉) in low-metallicity environments that lead to collapsar or magnetar-powered supernovae. It identifies key constraints from redshift, metallicity, and supernova associations, and evaluates mechanisms like disk winds, magnetic reconnection, and fallback accretion for powering late-time flares and ⁵⁶Ni production.

ABSTRACT

Most gamma-ray bursts are made during the deaths of massive stars. Here the environmental circumstances, stellar evolutionary paths, and explosion physics that might produce the bursts are reviewed. Neither of the two leading models - collapsar and millisecond magnetar - can be excluded, and both may operate in progenitor stars of different masses, metallicities, and rotation rates. Potential diagnostics are discussed and uncertainties highlighted. Both models are capable of producing a wide variety of transients whose properties vary with both stellar properties and viewing angle. Some of these are reviewed including the possibility of very long (days) low luminosity bursts, so far undiscovered, short hard bursts from massive stellar progenitors, and bursts from very massive Population III stars.

Motivation & Objective

• To clarify the astrophysical conditions under which long-soft gamma-ray bursts (LSBs) form, particularly focusing on massive star evolution and progenitor mass functions.
• To evaluate competing central engine models—collapsar and magnetar—against observational constraints from redshift, metallicity, and supernova associations.
• To investigate the role of angular momentum, mass loss, and fallback accretion in powering late-time flares and ⁵⁶Ni production in LSBs.
• To assess the viability of magnetar and collapsar models in explaining both the prompt emission and the energetic supernova remnants linked to LSBs.

Proposed method

• Analyzes observational data from Swift and pre-Swift missions to constrain the redshift distribution and host galaxy properties of LSBs.
• Applies analytic models of star-forming galaxies and stellar population evolution to estimate minimum progenitor masses (≥40 M☉) for LSBs.
• Evaluates the role of metallicity-dependent mass loss in shaping progenitor properties and favoring low-metallicity environments for LSB formation.
• Examines hydrodynamic and magnetic processes in proto-neutron stars and accretion disks, including differential rotation, magnetic field dissipation, and disk wind dynamics.
• Considers fallback accretion and oscillatory accretion cycles in massive stellar cores as mechanisms for late-time flares.
• Reviews theoretical models of magnetic reconnection and transient accretion to explain hard X-ray flares observed hundreds to thousands of seconds after the prompt emission.

Experimental results

Research questions

• RQ1 What is the minimum main-sequence mass of progenitor stars required to produce long-soft gamma-ray bursts, based on host galaxy and supernova association data?
• RQ2 How does low metallicity influence the formation of long-soft gamma-ray bursts through suppression of line- and grain-driven mass loss?
• RQ3 Can magnetar-powered models produce sufficient ⁵⁶Ni yield to power bright supernovae while also sustaining central engine activity for late flares?
• RQ4 What mechanisms—such as magnetic reconnection or fallback accretion—can explain the observed hard X-ray flares occurring hundreds to thousands of seconds after the prompt burst?
• RQ5 To what extent do the properties of associated supernovae and their host galaxies support the collapsar or magnetar model for long-soft GRB central engines?

Key findings

• The minimum progenitor mass for long-soft gamma-ray bursts is estimated to be above 40 M☉ based on analytic modeling of star-forming galaxies and stellar population evolution.
• Long-soft bursts are strongly associated with low-metallicity environments, with average host metallicity at 1/6 solar, and are preferentially found in faint, irregular galaxies with high star formation rates.
• The progenitor of GRB 030329 is constrained to have a main-sequence mass of at least 25 M☉, with only a small probability of being as low as 12 M☉.
• The progenitor of GRB 060505 is estimated to have had a mass of 32 M☉, supporting the link between massive stars and long-soft bursts.
• Late-time flares in long-soft bursts are likely powered by transient accretion or magnetic reconnection, with oscillatory fallback cycles in massive cores potentially driving periodic emission on ~100 s timescales.
• Both the magnetar and collapsar models can, in principle, produce sufficient ⁵⁶Ni to power bright supernovae, but the hydrodynamics of disk winds and fallback remain poorly constrained in realistic simulations.