Observation of a Long-Term Spin-up Trend in 4U 1538–52

The high-mass X-ray pulsar 4U 1538-52 has been continually monitored by the BATSE (Burst and Transient Source Experiment) on Compton Gamma-Ray Observatory. These observations permit the construction of long-term pulse frequency and intensity histories. The frequency history reveals that a reversal of the long-term trend in the accretion torque, from spinning down to spinning up, has occurred, probably in 1988. This is the first time a long-term change is known to have occurred for this source. The magnitude of the average | ν̇/ν |~10−11 s-1 over an interval of ~5 yr is similar during spin-down and spin-up. Shorter term pulse frequency variations of either sign are also observed. The power density spectrum of fluctuations in angular acceleration is consistent with white noise on timescales from 16 to 1600 days. It can be well fit with a power law with a power-law index of 0.10 ± 0.21 and white noise strength of (7.6 ± 1.6) × 10-21(Hz s-1)2 Hz-1. These observations are also used to set 95% confidence level lower and upper limits on the rate of orbital period change, -3.9

[1]  R. W. Nelson,et al.  On the Correlation of Torque and Luminosity in GX 1+4 , 1997, astro-ph/9703047.

[2]  L. Cominsky,et al.  Observations of 4U 1700-37 with BATSE , 1996 .

[3]  M. Tavani,et al.  Wind-driven angular momentum loss in binary systems. I - Ballistic case , 1993 .

[4]  S. Rappaport,et al.  Discovery of orbital decay in SMC X-1 , 1993 .

[5]  F. Frontera,et al.  EXOSAT Observations of the X-Ray Binary Pulsar 4U 1538-52 , 1992 .

[6]  C. Day,et al.  Ginga observations of Centaurus X-3 , 1992 .

[7]  R. Hilditch,et al.  Optical spectroscopy of the massive X-ray binary QV Nor (4U 1538 – 52)⋆ , 1992 .

[8]  L. Cominsky,et al.  Multimission observations of 4U 1538-52 , 1991 .

[9]  G. Clark,et al.  Discovery of a cyclotron absorption line in the spectrum of the binary X-ray pulsar 4U 1538 - 52 observed by Ginga , 1990 .

[10]  B. Fryxell,et al.  Numerical studies of asymmetric adiabatic accretion flow - The effect of velocity gradients , 1989 .

[11]  K. Koyama,et al.  Spectra and pulse period of the binary X-ray pulsar 4U 1538-52 , 1987 .

[12]  G. Zylstra,et al.  New evidence on the nature of the neutron star and accretion flow in Vela X-1 from pulse timing observations , 1984 .

[13]  J. E. Deeter,et al.  Techniques for the estimation of red power spectra. II Evaluation of alternative methods , 1984 .

[14]  N. White,et al.  Accretion powered X-ray pulsars , 1983 .

[15]  P. E. Boynton,et al.  Techniques for the estimation of red power spectra. I - Context and methodology , 1982 .

[16]  D. Crampton,et al.  Optical spectroscopy and system parameters for 4U 1538-52. , 1978 .

[17]  M. Watson,et al.  The binary X-ray pulsar 3U 1538–52 , 1977 .

[18]  R. Becker,et al.  A1540-53, an eclipsing X-ray binary pulsator , 1977 .

[19]  J. Wheeler,et al.  Tidal circularization of the binary x-ray sources hercules X-1 and centaurus X-3 AU Myron,Lecar , 1976 .

[20]  Thomas A. Prince,et al.  Torque Reversal and Spin-down of the Accretion-powered Pulsar 4U 1626–67 , 1997 .

[21]  G. Zylstra,et al.  Vela X-1 pulse timing. II - Variations in pulse frequency , 1989 .