Oral Presentation

Stacked Hilbert-Huang Transform and its Applications: From High-Energy Astrophysics to Gravitational-Wave Astrophysics

Author(s): Chin-Ping Hu (National Changhua University of Education)

Presenter: Chin-Ping Hu (National Changhua University of Education)

We propose an algorithm based on the Hilbert-Huang transform (HHT). It operates the ensemble mean on the time-frequency map instead of obtaining intrinsic mode functions with ensemble empirical mode decomposition. We have successfully tracked the evolution of quasi-periodic superorbital modulation of SMC X-1, chirp signal in the gravitational wave data collected by LIGO-Virgo-KAGRA collaboration, and simulated signal from core-collapse supernovae (CCSNe). We discovered a new excursion event of SMC X-1 in 2020--2021, suggesting the unpredictable chaotic nature of the superorbital modulation. The spin-up rate accelerated one year before the onset of this new excursion, which suggests a possible inside-out process connecting the spin-up acceleration and the superorbital excursion. Further analysis the pulse profile evolution suggests that the pulsed fraction may be connected to the superorbital excursion. In gravitational astrophysics, our time-frequency maps of binary black hole coalescence events show much better details compared to those wavelet spectra. Moreover, the oscillation in the instantaneous frequency caused by mode-mixing are greatly reduced. For the CCSNe data, the oscillation from the proto-neutron star and the radiation from the standing accretion shock instability can be precisely determined with the stacked HHT in detail. More importantly, the initial stage of different modes of oscillations can be clearly separated. These results provide new hints for further establishment of the detecting algorithm, and new probes to investigate the underlying physical mechanisms.