Timescale of twin-peak quasi-periodic oscillations and mass of accreting neutron stars

Abstract

Einstein's general relativity predicts that orbital motion of accreted gas approaching a neutron star (NS) in a NS low-mass X-ray binary (LMXB) system occurs on a time scale proportional to the NS mass. Radiation of the gas accounts for most of the observed LMXBs variability. In more than a dozen of sources twin-peak quasi-periodic oscillations (QPOs) have been observed. Inspired by the expected proportionality between periods of orbital motion and NS mass we present a straightforward comparison among these sources. We investigate relations between QPO periods and their ratios and identify characteristic time scales of QPOs associated to individual sources. These timescales are likely determined by the relative mass of each NS. We show that the characteristic time scale of the millisecond pulsar XTE J1807.4-294 is longer than for most other NS LMXBs. Consequently, models of QPOs that consider geodesic orbital frequencies imply that the X-ray pulsars' mass has to be about 50 % higher than the average mass of other sources. Consideration of other X-ray pulsars indicates that the exceptionality of XTE J1807.4-294 cannot be related to NS magnetic field in any simple manner. We suggest that QPOs observed in this source can help to discriminate between the proposed versions of the NS equation of state.

9 pages, 6 figures, 1 table, accepted for publication in MNRAS

References in corpus (18)

• X-ray Properties of Black-Hole Binaries
• A Parallax Distance to the Microquasar GRS 1915+105 and a Revised Estimate of its Black Hole Mass
• A 400 solar mass black hole in the Ultraluminous X-ray source M82 X-1 accreting close to its Eddington limit
• A 200-s Quasi-Periodicity Following the Tidal Disruption of a Star by a Dormant Black Hole
• The coherence of kHz quasi-periodic oscillations in the X-rays from accreting neutron stars
• Tidal effects on small bodies by massive black holes
• Is there a link between the neutron-star spin and the frequency of the kilohertz quasi-periodic oscillations?
• Universal scaling of the 3:2 twin-peak quasi-periodic oscillation frequencies with black hole mass and spin revisited
• Bright X-ray flares from Sgr A*
• Mass-angular-momentum relations implied by models of twin peak quasi-periodic oscillations
• Gravitational excitation of high frequency QPOs
• The aperiodic X-ray variability of the accreting millisecond pulsar SAX J1808.4-3658
• Upper-twin-peak quasiperiodic oscillation in x-ray binaries and the energy from tidal circularization of relativistic orbits
• Constraining models of twin peak quasi-periodic oscillations with realistic neutron star equations of state
• Mass of the active galactic nucleus black hole XMMUJ134736.6+173403
• Correlations between the frequencies of twin kHz QPOs and spins of neutron stars in LMXBs
• On one-parametric formula relating the frequencies of twin-peak quasi-periodic oscillations
• The Structure of a Quasi-Keplerian Accretion Disk around Magnetized Stars