The Bursting Behavior of 4U 1728-34: Parameters of a Neutron Star and Geometry of a NS-disk system

Abstract

We analyze a set of Type I X-ray bursts from the low mass X-ray binary 4U 1728 -34, observed with Rossi X-ray Timing Explorer (RXTE). and we implement an analytical model of X-ray spectral formation in the neutron star (NS) atmosphere during a burst. We infer the dependence of the neutron star mass and radius with respect to the assumed distance to the system using an analytical model of X-ray burst spectral formation. The model behavior clearly indicates that the burster atmosphere is helium-dominated. Our results strongly favor the soft equation of state (EOS) of NS for 4U 1728-34. We find that distance to the source should be within 4.5-5.0 kpc range. We obtain rather narrow constrains for the NS radius in 8.7-9.7 km range and interval 1.2-1.6 solar masses for NS mass for this particular distance range. We uncover a temporal behavior of red-shift corrected burst flux for the radial expansion episodes and we put forth a dynamical evolution scenario for the NS--accretion disk geometry during which an expanded envelope affects the accretion disk and increases the area of the neutron star exposed to the Earth observer. Our scenario enables us to explain the timing characteristics and peak flux variation observed during the burst expansion stage, which is now believed to be common phenomenon. In the framework of this scenario we provide a new method for the estimation of the inclination angle which leads to the value of 50 degrees for 4U 1728-34 .

arXiv comment8 pages, 3 figures and one table, accepted for publication in the Astrophysical Journal Letters

References in corpus (10)

• Is SAX J1808.4-3658 a Strange Star ?
• Precise Measurements of the Kilohertz Quasi-Periodic Oscillations in 4U 1728-34
• Correlations between kHz QPO and Low Frequency Features Attributed to Radial Oscillations and Diffusive Propagation in the Viscous Boundary Layer Around a Neutron Star
• Strong Correlation Between Noise Features at Low Frequency and the Kilohertz QPOs in the X-Ray Binary 4U 1728-34
• Eddington-limited X-ray Bursts as Distance Indicators. I. Systematic Trends and Spherical Symmetry in Bursts from 4U 1728-34
• The Long Term Stability of Oscillations During Thermonuclear X-ray Bursts: Constraining the Binary X-ray Mass Function
• An Atlas of Burst Oscillations and Spectral Properties in 4U 1728-34
• Three Type I X-ray bursts from Cyg X-2: Application of Analytical Models for Neutron Star Mass and Radius Determination
• The Effect of the Mass Accretion Rate on the Burst Oscillations in 4U 1728-34
• Spectra of the Expansion Stage of X-Ray Bursts

Cited by in corpus (20)

• Thermonuclear (type-I) X-ray bursts observed by the Rossi X-ray Timing Explorer
• Quark deconfinement and implications for the radius and the limiting mass of compact stars
• Periodic Thermonuclear X-ray Bursts from GS 1826-24 and the Fuel Composition as a Function of Accretion Rate
• Analysing the atolls: X-ray spectral transitions of accreting neutron stars
• Measurement of neutron star parameters: a review of methods for low-mass X-ray binaries
• Achromatic late-time variability in thermonuclear X-ray bursts - an accretion disk disrupted by a nova-like shell?
• The scenario of two families of compact stars 1. Equations of state, mass-radius relations and binary systems
• Ignition latitude and the shape of Type I X-ray bursts
• Rotational Broadening of Atomic Spectral Features from Neutron Stars
• The scenario of two families of compact stars 2. Transition from hadronic to quark matter and explosive phenomena
• On the nature of the flux variability during an expansion stage of a type I X-ray burst: Constraints on Neutron Star Parameters for 4U 1820-30
• Ultra-compact X-ray binaries as dual-line gravitational-wave sources
• The spectral-timing properties of upper and lower kHz QPOs
• Study of the X-ray properties of the neutron-star binary 4U 1728$-$34 from the soft to hard state
• Insight-HXMT observation on 4U~1608--52: evidence of interplay between thermonuclear burst and accretion environments
• Photospheric radius expansion during magnetar bursts
• The kHz QPOs as a probe of the X-ray color-color diagram and accretion-disk structure for the atoll source 4U 1728-34
• Insight-HXMT observations on thermonuclear X-ray bursts from 4U~1608--52 in 2022: the accretion rate dependent anisotropy of burst emission
• Return of 4U~1730--22 after 49 years silence: the peculiar burst properties of the 2021/2022 outbursts observed by Insight-HXMT
• Large frequency drifts during Type I X-ray bursts