Formation and evolution of binary and millisecond radio pulsars

Neutron Stars 1: Equation of State and Structure

Ordinary radio pulsars1 are neutron stars with magnetic fields of ∼1012 gauss and spin periods in the range 0.1 to 3 seconds. In contrast, millisecond radio pulsars2 have much weaker fields (∼109 gauss) and faster, millisecond spin rates. For both types of pulsar, the energy driving the radio pulsations is thought to be derived from the rotation of the neutron star. The star gradually ‘spins down’ as energy is radiated away. Millisecond radio pulsars are often located in binary systems3. In a widely accepted theoretical model4,5, they started as ordinary pulsars which lost most of their magnetic field and were ‘spun up’ to millisecond periods by the accretion of matter from a companion star in an X-ray binary system. Evidence6,7,8,9,10,11 for this model has gradually mounted, but direct proof—in the form of the predicted coherent millisecond X-ray pulsations in the persistent flux of an X-ray binary has been lacking, despite many searches12,13,14,15. Here we report the discovery16 of such a pulsar, confirming theoretical expectations. The source will probably become a millisecond radio pulsar when the accretion turns off completely.

A millisecond pulsar in an X-ray binary system

X-ray bursts

Preface 1. The properties of X-ray binaries, N. E. White, F. Nagase and A. N. Parmar 2. Optical and ultraviolet observations of X-ray binaries J. van Paradijs and J. E. McClintock 3. Black-hole binaries Y. Tanaka and W. H. G. Lewin 4. X-ray bursts Walter H. G. Lewin, Jan Van Paradijs and Ronald E. Taam 5. Millisecond pulsars D. Bhattacharya 6. Rapid aperiodic variability in binaries M. van der Klis 7. Radio properties of X-ray binaries R. M. Hjellming and X. Han 8. Cataclysmic variable stars France Anne-Dominic Cordova 9. Normal galaxies and their X-ray binary populations G. Fabbiano 10. Accretion in close binaries Andrew King 11. Formation and evolution of neutron stars and black holes in binaries F. Verbunt and E. P. J. van den Heuvel 12. The magnetic fields of neutron stars and their evolution D. Bhattacharya and G. Srinivasan 13. Cosmic gamma-ray bursts K. Hurley 14. A catalogue of X-ray binaries Jan van Paradijs 15. A compilation of cataclysmic binaries with known or suspected orbital periods Hans Ritter and Ulrich Kolb References Index.

http://www.gbv.de/dms/goettingen/152055878.pdf

X-ray binaries

The X-ray flux of the bright galactic bulge source GX5 - 1 shows intensity-dependent quasi-periodic oscillations between 20 and 40 Hz, appearing as a broad peak in the power spectrum whose centroid frequency, width, and integrated excess power strongly depend on the source intensity. The strength and steepness of low-frequency noise present in the power spectra below 15 Hz also depend on the source intensity. No evidence is found for coherent X-ray pulsations between 0.5 and 2000 Hz. Possible mechanisms to explain these new phenomena are discussed.

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Intensity-dependent quasi-periodic oscillations in the X-ray flux of GX5 - 1

The results of a study of quasi-periodic oscillations (QPOs) in Exosat observations of Sco X-1 made in August 1983 and March 1984 are reported. The observational details are given, and the properties of the QPOs and their dependence on the overall state of the source are discussed. The spectral dependence of the QPOs are examined in terms of two-component spectral model. The consequences of the results for magnetic and nonmagnetic neutron star models are considered. 53 references.

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Intensity and source state dependence of the quasi-periodic oscillations in Scorpius X-1

In a series of seven Exosat observations, the bimodal spectral behavior and the quasi-periodic oscillation (QPO)/red noise properties of GX 5-1 show a strict correlation. In one of the two spectral states (characterized by a 'horizontal branch' in the hardness-intensity diagram), strong 20-40 Hz QPO and red noise below about 60 Hz were always present. In the other ('normal branch'), no QPO between 6 and 60 Hz or red noise above 1 Hz were detected, but there was an indication for weak QPO near 5 Hz. In both states 'very low frequency noise' (VLFN) is detected below 0.1 Hz which has a power-law shape and and which extends down to the lowest observed frequencies (0.0001 Hz). The VLFN is probably not directly related to the QPO. The results are compared to those on Sco X-1 and Cyg X-2 and it is concluded that, although all three sources show bimodal spectral and QPO/red noise behavior, there is a qualitative difference between GX 5-1 and Cyg X-2 on one hand and Sco X-1 on the other.

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Correlation between spectral state and quasi-periodic oscillation parameters in GX 5-1

Cygnus X-3, a bright X-ray source at a distance1 of more than ∼12 kpc beyond the edge of the galactic plane, has peculiar properties including very strong radio outbursts2, possibly showing jet-like features3, and emission in various γ-ray bands4–6 (but see ref. 7). The discovery of its 4.8-h X-ray period8 showed that the source is probably a compact (∼1011 cm) binary system, but its nature and that of its companion, the mode of energy generation (accretion or Crab-like pulsar) and also the cause of the X-ray modulation are still uncertain. We describe here X-ray data on Cyg X-3, obtained with EXOSAT, showing transient quasi-periodic oscillations with amplitudes between 5 and 20% of the 1–10-keV flux and periods in the range 50–1,500 s. The oscillations persisted typically for 5–40 (quasi-oscillation) cycles, occurred exclusively in the phase interval 0.0–0.75 (rising branch and top of the X-ray light curve), were seen during the high state and probably also during the low state of the source, and, at least once, were observed with two different periods simultaneously. We suggest that the quasi-periodic flux variations are caused by quasi-periodic phenomena in an accretion disk which partially occults the X-ray source. This tentative interpretation is in accordance with the idea9 that the 4.8-h modulation of the X-ray flux in Cyg X-3 arises by partial occultations of the X-ray source by an accretion disk, like in low-mass X-ray binaries such as 4U1822–37.

Transient quasi-periodic oscillations in the X-ray flux of Cygnus X-3

Exosat observations of GX3+1 in 1985 showed the presence of low-frequency noise (LFN) roughly below 10 Hz, and the presence, during the September 4 observation, of quasi-periodic oscillations (QPOs) with a strength of about 3 percent. The LFN strength was seen to increase from 2-6 percent for photon energies increasing from 2-10 keV. No correlation is found between the occurrence of QPOs and source intensity. It is suggested that the QPOs detected in GX3+1 may be similar in nature to the 5.6-Hz QPOs observed in Cyg X-2 which are also not observed in the horizontal branch.

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F. Jansen

Papers

Intensity-dependent quasi-periodic oscillations in the X-ray flux of GX5 - 1

Intensity and source state dependence of the quasi-periodic oscillations in Scorpius X-1

Correlation between spectral state and quasi-periodic oscillation parameters in GX 5-1

Transient quasi-periodic oscillations in the X-ray flux of Cygnus X-3

Quasi-periodic oscillations in the X-ray flux of GX3+1 (4U 1744-26)