Characteristics of the High-frequency Humps in the Black hole X-ray Binary Swift J1727.8--1613

TL;DR

This study analyzes high-frequency humps in the X-ray power spectrum of Swift J1727.8--1613, revealing their energy-dependent properties and using relativistic precession modeling to estimate the black hole's mass and spin.

Contribution

It provides the first detailed energy-dependent timing analysis of high-frequency humps and constrains black hole parameters using the relativistic precession model.

Findings

Hump frequencies increase with energy up to ~30 keV and then plateau.

Fractional rms amplitudes reach about 15% in 50-100 keV band.

Black hole mass estimated between 2.84 and 120.01 solar masses, spin between 0.14 and 0.43.

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 $\sim30$ 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 $2.84 < M / M_{\odot} < 120.01$ and the spin to $0.14 < a < 0.43$ from the full-energy band dataset, using triplets composed of a type-C quasi-periodic oscillation and two high-frequency humps. When considering only the high-energy bands with stable characteristic frequencies, we derive additional constraints of $2.84 < M/M_{\odot} < 13.98$ and $0.14 < a < 0.40$.