Broad iron emission line and kilohertz quasi-periodic oscillations in the neutron star system 4U 1636-53

Abstract

Both the broad iron (Fe) line and the frequency of the kilohertz quasi-periodic oscillations (kHz QPOs) in neutron star low-mass X-ray binaries (LMXBs) can potentially provide independent measures of the inner radius of the accretion disc. We use XMM-Newton and simultaneous Rossi X-ray Timing Explorer observations of the LMXB 4U 1636-53 to test this hypothesis. We study the properties of the Fe-K emission line as a function of the spectral state of the source and the frequency of the kHz QPOs. We find that the inner radius of the accretion disc deduced from the frequency of the upper kHz QPO varies as a function of the position of the source in the colour-colour diagram, in accordance with previous work and with the standard scenario of accretion disc geometry. On the contrary, the inner disc radius deduced from the profile of the Fe line is not correlated with the spectral state of the source. The values of the inner radius inferred from kHz QPOs and Fe lines, in four observations, do not lead to a consistent value of the neutron star mass, regardless of the model used to fit the Fe line. Our results suggest that either the kHz QPO or the standard relativistic Fe line interpretation does not apply for this system. Furthermore, the simultaneous detection of kHz QPOs and broad Fe lines is difficult to reconcile with models in which the broadening of the Fe line is due to the reprocessing of photons in an outflowing wind.

12 pages, 6 figures, Accepted for publication in MNRAS

References in corpus (15)

• Neutron Star Observations: Prognosis for Equation of State Constraints
• Modelling the behaviour of accretion flows in X-ray binaries
• Relativistic X-ray Lines from the Inner Accretion Disks Around Black Holes
• 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 time variability across the atoll source states of 4U 1636--53
• XMM-Newton detects a relativistically broadened iron line in the spectrum of the ms X-ray pulsar SAX J1808.4-3658
• Evidence of a Broad Relativistic Iron Line from the Neutron Star Low-Mass X-ray Binary Serpens X-1
• A relativistically smeared spectrum in the neutron star X-ray Binary 4U 1705-44: Looking at the inner accretion disc with X-ray spectroscopy
• Effects of Downscattering on the Continuum and Line Spectra in Powerful Wind Environment. Monte Carlo Simulations, Analytical Results and Data Analysis
• RossiXTE monitoring of 4U 1636-53: I. Long-term evolution and kHz Quasi-Periodic Oscillations
• Is there a link between the neutron-star spin and the frequency of the kilohertz quasi-periodic oscillations?
• Disk reflection signatures in the spectrum of the bright Z-source GX 340+0
• On the Non-relativistic Origin of Red-skewed Iron Lines in CV, Neutron Star and Black Hole Sources
• Discovery of kilohertz quasi-periodic oscillations and state transitions in the low-mass X-ray binary 1E~1724-3045 (Terzan 2)

Cited by in corpus (7)

• A Hard Look at the Neutron Stars and Accretion Disks in 4U 1636-53, GX 17+2, and 4U 1705-44 with $\text{NuSTAR}$
• Dense Matter in Neutron Stars with eXTP
• The reflection spectrum of the low-mass X-ray binary 4U 1636-53
• Study of the X-ray properties of the neutron-star binary 4U 1728$-$34 from the soft to hard state
• High-frequency variability in neutron-star low-mass X-ray binaries
• Correlations between the frequencies of twin kHz QPOs and spins of neutron stars in LMXBs
• Probing the accretion disc structure by the twin kHz QPOs and spins of neutron stars in LMXBs