The Effect of the Mass Accretion Rate on the Burst Oscillations in 4U 1728-34

Abstract

We present a comprehensive study of the properties of nearly coherent brightness oscillations (NCOs) in a large sample of type-I X-ray bursts observed from low mass X-ray binary 4U 1728-34. We have analyzed ~545ks of data of this source obtained with the Rossi X-ray Timing Explorer over a 3 year span from 1996-1999. The data contain 38 bursts, 16 of which show NCOs. We find no NCOs present when the inferred mass accretion rate of the system is lowest. Furthermore, we define a measure of the strength of the oscillations and find that this strength increases with increasing mass accretion rate. This correlation is particularly evident within bursts detected only a few weeks apart, and becomes less clear for bursts separated in time by several months to years. The correlation we find for 4U 1728-34 between the NCOs and the inferred accretion rate of the system is similar to that found for KS 1731-260 by Muno et al. (2000), where the NCOs are only present at relatively high mass accretion rates. However, unlike the case for KS 1731-260, we find an anti-correlation in the bursts of 4U 1728-34 between the existence of episodes of photospheric radius expansion and the inferred mass accretion rate of the system. Moreover, we distinguish between NCOs present in the rise and in the decay phase of the burst and find that the bursts with NCOs only in the decay phase occur at intermediate accretion rates, while those with NCOs in both the rise and the decay phases are concentrated at high inferred mass accretion rates. We discuss these results in the context of the theory of thermonuclear bursts and propose intrinsic differences in the neutron stars in KS 1731-260 and 4U 1728-34 as the origin of the different behaviors.

12 pages, 6 figures, 4 tables, to be submitted to ApJ, uses emulateapj5.sty (included)

References in corpus (6)

• Millisecond Oscillations in X-Ray Binaries
• Hard X-ray Emission From Low Mass X-ray Binaries
• Rotational Evolution During Type I X-Ray Bursts
• Nearly Coherent Oscillations in Type I X-Ray Bursts from KS 1731-260
• Study of the Temporal Behavior of 4U 1728-34 as a Function of its Position in the Color-Color Diagram
• The Broad Band Spectrum of MXB 1728-34 Observed by BeppoSAX

Cited by in corpus (21)

• Thermonuclear (type-I) X-ray bursts observed by the Rossi X-ray Timing Explorer
• Photospheric radius expansion X-ray bursts as standard candles
• The Multi-INstrument Burst ARchive (MINBAR)
• A multi-Lorentzian timing study of the atoll sources 4U 0614+09 and 4U 1728-34
• Eddington-limited X-ray Bursts as Distance Indicators. I. Systematic Trends and Spherical Symmetry in Bursts from 4U 1728-34
• Thermonuclear X-ray Bursts: Theory vs. Observations
• The X-ray spectrum of the bursting atoll source 4U~1728-34 observed with INTEGRAL
• The Energy Dependence of Millisecond Oscillations in Thermonuclear X-ray Bursts
• The Effect of Neutron Star Rotation on the Properties of Thermonuclear X-ray Bursts
• The Bursting Behavior of 4U 1728-34: Parameters of a Neutron Star and Geometry of a NS-disk system
• On the Constancy of the Photon Index of X-ray spectra of 4U~1728-34 through all spectral states
• The burst behavior of the eclipsing low-mass X-ray binary MXB 1659-298
• Latitudinal Shear Instabilities during Type I X-ray Bursts
• The new X-ray transient SAX J1711.6-3808: decoupling between its 3-20 keV luminosity and its state transitions
• Coherent oscillations and the evolution of the emission area in the decaying phase of radius-expansion bursts from 4U 1636-53
• Generation of Type I X-ray Burst Oscillations by Unstable Surface Modes
• Discovery of type-I X-ray bursts from the low-mass X-ray binary 4U 1708-40
• NICER Observation of Unusual Burst Oscillations in 4U 1728-34
• Burning in the tail: implications for a burst oscillation model
• Stability of strange stars (SS) derived from a realistic equation of state
• Incompressibility of strange matter