Characteristics of the high-frequency humps in the black hole X-ray binary Swift J1727.8–1613

¹ Key Laboratory for Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences 19B Yuquan Road Beijing 100049, China
² University of Chinese Academy of Sciences, Chinese Academy of Sciences Beijing 100049, China
³ Department of Physics and Astronomy, University of Southampton Highfield Southampton SO17 1BJ, UK
⁴ School of Physics and Optoelectronic Engineering, Shandong University of Technology Zibo 255000, China
⁵ Key Laboratory of Space Astronomy and Technology, National Astronomical Observatories, Chinese Academy of Sciences Beijing 100101, China

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Received: 23 April 2025
Accepted: 6 January 2026

Abstract

We present a detailed timing analysis of the two high-frequency humps observed in the power density spectrum of Swift J1727.8–1613 up to 100 keV, using data from the Hard X-ray Modulation Telescope (Insight-HXMT). Our analysis reveals that the characteristic frequencies of the humps increase with energy up to ∼30 keV, followed by a plateau at higher energies. The fractional rms amplitudes of the humps increase with energy, reaching approximately 15% in the 50–100 keV band. The lag spectrum of the hump is characterized primarily by a soft lag that varies with energy. Our results suggest that the high-frequency humps originate from a corona close to the black hole. Additionally, by applying the relativistic precession model, we constrain the mass of Swift J1727.8–1613 to 2.84 < M/M_⊙ < 120.01 and the spin to 0.14 < a < 0.43 from the full-energy-band dataset, using triplets composed of a type-C quasiperiodic oscillation and two high-frequency humps. When considering only the high-energy bands with stable characteristic frequencies, we derive additional constraints of 2.84 < M/M_⊙ < 13.98 and 0.14 < a < 0.40.