Hilbert–Huang Transform Analysis of Quasiperiodic Oscillations in MAXI J1820+070

Abstract We present a time-frequency analysis, based on the Hilbert–Huang transform, of evolution low-frequency quasiperiodic oscillations observed in black hole X-ray binary MAXI J1820+070. Through empirical mode decomposition method, we decompose light curve oscillation (QPO) component and measure its intrinsic phase lag between photons from different energy bands. find that QPO is negative (low-energy behind high-energy photons); meanwhile, absolute value increases with energy. By applying Hilbert transform to QPO, further extract instantaneous frequency amplitude QPO. Comparing these results those Fourier broadening peak mainly caused by modulation. modulations could share common physical origin broadband noise, can be well explained internal shock model jet.