[Paper Review] Gravitational Wave Signals from Two-Dimensional Core-Collapse Supernova Models with Rotation and Magnetic Fields

Rylan Jardine, J. Powell+1 more|arXiv (Cornell University)|May 4, 2021

Pulsars and Gravitational Waves Research10 references4 citations

TL;DR

This study investigates gravitational wave (GW) signals from 2D core-collapse supernova models with rotation and magnetic fields using neutrino-radiation hydrodynamics. It finds that rapid rotation and strong magnetic fields (up to 10¹² G) significantly alter the time-frequency structure of GW emission, disrupting standard analytic frequency relations and producing unique signatures like high-amplitude tail signals in magnetorotational explosions, though detectability remains comparable to non-magnetized models.

ABSTRACT

We investigate the impact of rotation and magnetic fields on the dynamics and gravitational wave emission in 2D core-collapse supernova simulations with neutrino transport. We simulate 17 different models of $15\,M_\odot$ and $39\,M_\odot$ progenitor stars with various initial rotation profiles and initial magnetic fields strengths up to $10^{12}\, \mathrm{G}$, assuming a dipolar field geometry in the progenitor. Strong magnetic fields generally prove conducive to shock revival, though this trend is not without exceptions. The impact of rotation on the post-bounce dynamics is more variegated, in line with previous studies. A significant impact on the time-frequency structure of the gravitational wave signal is found only for rapid rotation or strong initial fields. For rapid rotation, the angular momentum gradient at the proto-neutron star surface can appreciably affect the frequency of the dominant mode, so that known analytic relations for the high-frequency emission band no longer hold. In case of two magnetorotational explosion models, the deviation from these analytic relations is even more pronounced. One of the magnetorotational explosions has been evolved to more than half a second after the onset of the explosion and shows a subsidence of high-frequency emission at late times. Its most conspicuous gravitational wave signature is a high-amplitude tail signal. We also estimate the maximum detection distances for our waveforms. The magnetorotational models do not stick out for higher detectability during the post-bounce and explosion phase.

Motivation & Objective

• To understand how rotation and magnetic fields influence the dynamics and gravitational wave (GW) emission in core-collapse supernovae.
• To assess the impact of strong magnetic fields (up to 10¹² G) and rapid rotation on shock revival and explosion success.
• To investigate deviations from established analytic relations for GW frequency in the post-bounce phase under magnetorotational conditions.
• To estimate maximum detection distances for GW signals from these models using current and future detectors.
• To identify unique GW signatures—such as tail signals—that could distinguish magnetorotational explosions from standard neutrino-driven events.

Proposed method

• Simulates 17 two-dimensional core-collapse supernova models of 15 M⊙ and 39 M⊙ progenitors with varying initial rotation profiles and magnetic field strengths.
• Uses neutrino-radiation hydrodynamics with a dipolar magnetic field geometry in the progenitor, evolving models from core bounce to over 500 ms post-bounce.
• Applies linear eigenmode analysis to identify the nature of oscillation modes in GW spectrograms, particularly f- and g-modes.
• Compares time-frequency structures of GW signals against known analytic relations for f/g-mode frequencies, especially under rapid rotation or strong magnetization.
• Estimates maximum detection distances for Advanced LIGO and the Einstein Telescope using simulated waveforms and signal-to-noise ratio considerations.
• Analyzes the matter and GW signals to identify anisotropic emission features, such as high-amplitude tail signals in magnetorotational explosions.

Experimental results

Research questions

• RQ1 How do strong magnetic fields and rapid rotation affect shock revival and explosion dynamics in 2D core-collapse supernova models?
• RQ2 To what extent do rotation and magnetic fields disrupt the standard analytic relation for the dominant f/g-mode frequency in GW emission?
• RQ3 What unique gravitational wave signatures emerge in magnetorotational explosion models, particularly in the time-frequency domain?
• RQ4 How do the amplitudes and energy content of GW signals compare across different progenitor masses and magnetic/rotational conditions?
• RQ5 What are the maximum detection distances for these GW signals with current (Advanced LIGO) and future (Einstein Telescope) detectors?

Key findings

• Strong magnetic fields generally promote shock revival, though exceptions exist, and magnetic fields can significantly alter the post-bounce dynamics.
• Rapid rotation increases the angular momentum gradient at the proto-neutron star surface, raising the dominant f/g-mode frequency by up to 20%, invalidating standard analytic frequency relations.
• In magnetorotational explosion models, the high-frequency emission band deviates markedly from standard relations, with a single dominant mode persisting, likely a modified f/g-mode.
• One 15 M⊙ magnetorotational explosion model evolved beyond 500 ms shows a subsiding high-frequency emission and a prominent high-amplitude tail signal in the GW waveform.
• The estimated maximum detection distances range from several 10 kpc to 140 kpc for Advanced LIGO and 0.6–2.6 Mpc for the Einstein Telescope, with no significant detectability advantage for magnetorotational models.
• The 39 M⊙ magnetorotational explosion is potentially detectable throughout the Local Group, suggesting a ~10% per-century chance of observing a hypernova in GWs.