Evidence from Quasi-periodic Oscillations for a Millisecond Pulsar in the Low-Mass X-Ray Binary 4U 0614+091

Abstract

We have detected quasi-periodic oscillations (QPOs) near 1 kHz from the low mass X-ray binary 4U 0614+091 in observations with XTE. The observations span several months and sample the source over a large range of X-ray luminosity. In every interval QPOs are present above 400 Hz with fractional RMS amplitudes from 3 to 12%. At high count rates, two high frequency QPOs are detected simultaneously. The difference of their frequency centroids is consistent with 323 Hz in all observations. During one interval a third signal is detected at 328 ± 2 Hz. This suggests the system has a stable 'clock' which is most likely the neutron star with spin period 3.1 msec. Thus, our observations and those of another neutron star system by Strohmayer et al. (1996) provide the first evidence for millisecond pulsars within low-mass X-ray binary systems and reveal the 'missing-link' between millisecond radiopulsars and the late stages of binary evolution in low mass X-ray binaries (Alpar et al. 1982). We suggest that the kinematics of the magnetospheric beat-frequency model applies to these QPOs. In this interpretation the high frequency signal is associated with the Keplerian frequency of the inner accretion disk and the lower frequency 'beat' signal arises from the differential rotation frequency of the inner disk and the spinning neutron star. Assuming the high frequency QPO is a Keplerian orbital frequency for the accretion disk, we find a maximum mass of 1.9M ⊙ and a maximum radius of 17 km for the neutron star.

On the Magnetospheric Beat‐Frequency and Lense‐Thirring Interpretations of the Horizontal‐Branch Oscillation in the Z Sources

“…Here we explore the consequences of the simple Ansatz where and j are constants that l 2 \ l 0 (M 0 /M 0 E )j, l 0 are speciÐc to each source and may depend on the mass and magnetic Ðeld strength of the neutron star. This relation, with j B 1, is consistent with kilohertz QPO observations of several atoll sources, provided that the observed count rate from an atoll source is proportional to the mass accretion rate (see, e.g., Strohmayer et al 1996 ;Ford et al 1997). In the Z sources, is consistent with being^1200 Hz l 2 when they are accreting at near-Eddington rates, which implies Hz, independent of the expected modest l 0 B 1200 di †erences in the masses and magnetic Ðeld strengths of these neutron stars.…”

Long-term luminosity behavior of 14 ultracompact X-ray binaries

“…References. 1) Stella et al (1987); 2) Kuulkers et al (2003) White & Swank (1982); 38) Walter et al (1982); 39) Galloway et al (2008); 40) Becker et al (1977); 41) Lewin et al (1977); 42) Krimm et al (2007); 43) Altamirano et al (2010); 44) Ortolani et al (1994); 45) Galloway et al (2010); 46) Wilson-Hodge et al (2012); 47) Lewin et al (1976); 48) Hoffman et al (1976); 49) Strohmayer et al (1996); 50) Deutsch et al (2000); 51) in't Zand et al (1998); 52) Shahbaz et al (2008); 53) Hakala et al (2011); 54) Zhang et al (2012); 55) Kuulkers et al (2010); 56) Madej et al (2010); 57) Swank et al (1978); 58) Brandt et al (1992); 59) Ford et al (1997) Galactic plane. Table 1 presents an updated version of the UCXB and UCXB candidate overviews in in't Zand et al (2007), Lasota et al (2008) and Nelemans & Jonker (2010).…”

Synthesis of the elements in stars: forty years of progress

“…In LMXBs with subgiant donors, the electron-degenerate core survives as a helium WD and the final system is a binary MSP. Comparison between a measured beat period and the Keplerian period permits one to infer the spin period of the NS in an LMXB (Alpar and Shaham, 1985;Lamb et al, 1985;Gosh and Lamb, 1992), and this has been accomplished in three LMXBs (Strohmayer et al, 1996;Morgan and Smith, 1996;Ford et al, 1997).…”