Discovery of Red-Skewed K_alpha iron line in Cyg X-2 with Suzaku

Abstract

We report on the Suzaku observation of neutron star low-mass X-ray binary Cygnus X-2 which reveals a presence of the iron K_alpha emission line. The line profile shows a significant red wing. This discovery increases the number of neutron star sources where red-skewed iron lines were observed and strongly suggests that this phenomenon is common not only in black holes but also in other types of accreting compact objects. We examine the line profile in terms of models which attribute its production to the relativistic effects due to reflection of X-ray radiation from a cold accretion disk and also as a result of the line formation in the extended wind/outflow configuration. Both models are able to adequately represent the observed line profile. We consider the results of line modeling in the context of subsecond variability. While we were unable to conclusively disqualify one of the models, we find that the wind paradigm has several advantages over the relativistic disk reflection model.

accepted for publication in ApJ

References in corpus (8)

• Neutron Star Observations: Prognosis for Equation of State Constraints
• 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
• Multi-dimensional modelling of X-ray spectra for AGN accretion-disk outflows
• Average hard X-ray emission from NS LMXBs: Observational evidence of different spectral states in NS LMXBs
• Evidence of a Broad Relativistic Iron Line from the Neutron Star Low-Mass X-ray Binary Serpens X-1
• Effects of Downscattering on the Continuum and Line Spectra in Powerful Wind Environment. Monte Carlo Simulations, Analytical Results and Data Analysis
• Correlations between X-ray Spectral and Timing Characteristics in Cyg X-2

Cited by in corpus (7)

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• NuSTAR view of the Z-type neutron star low-mass X-ray binary Cygnus~X--2
• High-frequency variability in neutron-star low-mass X-ray binaries
• Thermonuclear X-ray bursts detected in Cyg X-2 using AstroSat/LAXPC
• Probing the accretion geometry of the atoll source 4U 1702-429 in different spectral states with NICER, NuSTAR, and AstroSat
• Red-skewed K$\alpha$ iron lines in GX 13+1