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A Linear and Quadratic Time–Frequency Analysis of Gravitational Waves from Core-collapse Supernovae

Authors :
Kazuhiro Hayama
Tomoya Takiwaki
Kei Kotake
Takami Kuroda
Hajime Kawahara
Source :
The Astrophysical Journal

Abstract

Recent core-collapse supernova (CCSN) simulations have predicted several distinct features in gravitational-wave (GW) spectrograms, including a ramp-up signature due to the g-mode oscillation of the proto-neutron star (PNS) and an excess in the low-frequency domain (100-300 Hz) potentially induced by the standing accretion shock instability (SASI). These predictions motivated us to perform a sophisticated time-frequency analysis (TFA) of the GW signals, aimed at preparation for future observations. By reanalyzing a gravitational waveform obtained in a three-dimensional general-relativistic CCSN simulation, we show that both the spectrogram with an adequate window and the quadratic TFA separate the multimodal GW signatures much more clearly compared with the previous analysis. We find that the observed low-frequency excess during the SASI active phase is divided into two components, a stronger one at 130 Hz and an overtone at 260 Hz, both of which evolve quasi-statically during the simulation time. We also identify a new mode whose frequency varies from 700 to 600 Hz. Furthermore, we develop the quadratic TFA for the Stokes I, Q, U, and V parameters as a new tool to investigate the GW circular polarization. We demonstrate that the polarization states that randomly change with time after bounce are associated with the PNS g-mode oscillation, whereas a slowly changing polarization state in the low-frequency domain is connected to the PNS core oscillation. This study demonstrates the capability of the sophisticated TFA for diagnosing the polarized CCSN GWs in order to explore their complex nature.<br />Comment: 14 pages,18 figures. Accepted for publication in ApJ. The code for the time-frequency analysis used in the paper is available here: https://github.com/HajimeKawahara/juwvid

Details

Language :
English
ISSN :
15384357, 0004637X, 00046361, and 02649381
Volume :
867
Issue :
2
Database :
OpenAIRE
Journal :
The Astrophysical Journal
Accession number :
edsair.doi.dedup.....d7c7878ed27c7d4c478bd5f835d152e1
Full Text :
https://doi.org/10.3847/1538-4357/aae57b