Modeling the upper kHz QPOs of 4U 1728-34 with X-ray reverberation

Abstract

While kilohertz quasi-periodic oscillations (kHz QPOs) have been well studied for decades since their initial discovery, the cause of these signals remains unknown, as no model has been able to accurately predict all of their spectral and timing properties. Separately, X-ray reverberation lags have been detected in AGN and stellar-mass black hole binaries, and reverberation may be expected to occur in neutron star systems as well, producing lags of the same amplitude as the lags measured of the kHz QPOs. Furthermore, the detection of a relativistically reflected Fe K line in the time-averaged spectra of many neutron star systems provides an additional motivation for testing reverberation. While it has been shown that the lag-energy properties of the lower kHz QPOs are unlikely to be produced by X-ray reverberation, the upper kHz QPOs have not yet been explored. We therefore model the upper kHz QPO lag-energy spectra using relativistic ray-tracing functions and apply them to archival RXTE data on 4U 1728-34 where upper kHz QPOs have been detected. By modeling the time-averaged spectra in which upper kHz QPOs had been significantly detected, we determine the reflected flux fraction across all energies and produce a model for the lag-energy spectra from X-ray reverberation. We explore the dependence of the modeled lag properties on several different types of reflection models, but are unable to successfully reproduce the measured lags of 4U 1728-34. We conclude that reverberation alone does not explain the measured time lags detected in upper kHz QPOs.

Accepted for publication in ApJ. 16 pages, 7 figures

References in corpus (25)

• X-ray reverberation around accreting black holes
• The role of the reflection fraction in constraining black hole spin
• The corona contracts in a black-hole transient
• Evaluating Spectral Models and the X-ray States of Neutron-Star X-ray Transients
• Relativistic iron emission lines in neutron star low-mass X-ray binaries as probes of neutron star radii
• Broad relativistic iron emission line observed in SAX J1808.4-3658
• X-ray reflection in accreting stellar-mass black hole systems
• A public relativistic transfer function model for X-ray reverberation mapping of accreting black holes
• The coherence of kHz quasi-periodic oscillations in the X-rays from accreting neutron stars
• The Comptonising medium of the neutron star in 4U 1636-53 through its lower kilohertz Quasi-Periodic Oscillations
• Evidence of a Broad Relativistic Iron Line from the Neutron Star Low-Mass X-ray Binary Serpens X-1
• Discovery of a ~2 hr high frequency X-ray QPO and iron K alpha reverberation in the active galaxy MS 2254.9-3712
• A Hard Look at the Neutron Stars and Accretion Disks in 4U 1636-53, GX 17+2, and 4U 1705-44 with $\text{NuSTAR}$
• Iron K and Compton hump reverberation in SWIFT J2127.4+5654 and NGC 1365 revealed by NuSTAR and XMM-Newton
• NuSTAR Observations of the Accreting Atolls GX 3+1, 4U 1702-429, 4U 0614+091, and 4U 1746-371
• Observations of MCG-5-23-16 with Suzaku, XMM-Newton and NuSTAR: Disk tomography and Compton hump reverberation
• Multi-timescale X-ray reverberation mapping of accreting black holes
• Energy Dependent Time Delays of kHz Oscillations due to Thermal Comptonization
• Suzaku broad-band spectrum of 4U 1705-44: Probing the Reflection component in the hard state
• Revealing structure and evolution within the corona of the Seyfert galaxy I Zw 1
• An X-ray reverberation mass measurement of Cygnus X-1
• Simultaneous spectral and reverberation modelling of relativistic reflection in Mrk 335
• Study of the X-ray properties of the neutron-star binary 4U 1728$-$34 from the soft to hard state
• The amplitude of the kilohertz quasi-periodic oscillations in 4U 1636$-$53 in the frequency-energy space
• Spectral-Timing Analysis of the Lower kHz QPO in the Low-Mass X-ray Binary Aquila X-1

Cited by in corpus (3)

• High-frequency variability in neutron-star low-mass X-ray binaries
• Kilohertz quasi-periodic oscillations in neutron-star X-ray binaries: Flattening of the lag spectrum with increasing luminosity
• Pulse profile modelling of the accretion-powered millisecond pulsar SAX J1808.4-3658 using NICER data from its 2019 and 2022 outbursts