The First Polarimetric View on Quasiperiodic Oscillations in a Black Hole X-Ray Binary

Abstract

We present the first polarimetric analysis of quasiperiodic oscillations (QPOs) in a black hole binary utilizing IXPE data. Our study focuses on Swift J1727.8–1613, which experienced a massive outburst that was observed by various telescopes across different wavelengths. The IXPE observation we studied was conducted during the hard-intermediate state. The polarization degree (PD) and polarization angle (PA) were measured at 4.28% ± 0.20% and 1.°9 ± 1.°4, respectively. Remarkably, significant QPO signals were detected during this observation, with a QPO frequency of approximately 1.34 Hz and a fractional rms amplitude of about 12.3%. Furthermore, we conducted a phase-resolved analysis of the QPO using the Hilbert–Huang transform technique. The photon index showed a strong modulation with respect to the QPO phase. In contrast, the PD and PA exhibit no modulations in relation to the QPO phase, which is inconsistent with the expectation of the Lense–Thirring precession of the inner flow. Further theoretical studies are needed to conform with the observational results.

Energy Dependence of the Low-frequency Quasiperiodic Oscillations in Swift J1727.8–1613

“…Meanwhile, the hard X-ray flux measured by MAXI and Swift/BAT continues its descent. In Figure 2, we depict the HID of Swift J1727.8−1613, which aligns with the evolutionary trajectory obtained in previous studies (Nandi et al 2024;Peng et al 2024;Zhao et al 2024).…”

“…The inconsistency in inclination estimates may arise from the L-T precession model not fully applying to Swift J1727.8-1613. Zhao et al (2024) conducted an analysis of the polarimetric data of this source and performed a phase-resolved analysis of the QPO using the Hilbert-Huang transform technique. The photon index displayed a significant modulation relative to the QPO phase.…”

“…Furthermore, the alignment of the X-ray polarization angle with that observed in submillimeter wavelengths suggests that the corona's elongation is orthogonal to the jet direction (Ingram et al 2023). Zhao et al (2024) presented the first polarimetric analysis of QPOs in Swift J1727.8−1613 utilizing IXPE data. Subsequent phase-resolved analysis of the QPO, utilizing the Hilbert-Huang transform technique, unveiled a significant modulation of the photon index in relation to the QPO phase.…”

A Timing View of the Additional High-energy Spectral Component Discovered in the Black Hole Candidate Swift J1727.8-1613

“…As the outburst evolves, Svoboda et al (2024) found that the polarization degree decreases dramatically to 1% in the soft state, which suggested that the polarization is mainly contributed by the upscattered radiation in the hot corona. Meanwhile, based on a phase-resolved polarimetric analysis, Zhao et al (2024) found no modulations of polarization degree and polarization angle with the QPO phase in the 2-8 keV band for the same observation. This result poses a challenge to the hot flow precession model for Swift J1727.8-1613.…”

Dramatic Drop in the X-Ray Polarization of Swift J1727.8–1613 in the Soft Spectral State

“…−16:12:19.23) was initially detected on 2023 August 24 (Kennea & Swift Team 2023;Negoro et al 2023), showing a remarkably intense outburst peaking at around 7Crab in the 2-20 keV energy range. A comprehensive evaluation of the source characteristics strongly supports its classification as a BHXRB from its X-ray spectrum (Liu et al 2023;Sunyaev et al 2023;Peng et al 2024), the identification of type C quasiperiodic oscillations (Bollemeijer et al 2023;Draghis et al 2023;Palmer & Parsotan 2023;Zhao et al 2024), and the detection of flat-spectrum radio emission indicative of a compact jet (Bright et al 2023;Miller-Jones et al 2023). The presence of the black hole in this X-ray binary is also suggested from the optical spectroscopy (Mata Sánchez et al 2024).…”