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Ejectors in Massive Binary Systems


After 25 years of pulsar studies, a radiopulsar has been discovered in a binary system with a massive optical companion (Johnston et al., 1992)[78]. This discovery is excellent confirmation of the modern theory of evolution of binary stars including the evolution of magnetized compact stars depicted above. As shown in the very first calculations of joint evolution of NS and normal stars in binaries (Kornilov and Lipunov, 1983b[86]) a considerable fraction (maybe, the majority) of NS in binary systems having an optical companion must be at the ejector  (E) state. A NS in this state generates a relativistic wind  like an isolated radiopulsar (Figure 5).

It was also shown that for a remote observer some NS in these binaries can appear as radiopulsars (Kornilov and Lipunov, 1984[87]). But the number of the binary radiopulsars with optical companions actually observed can be significantly suppressed for the following three main reasons.

  1. The absorption of radiowaves in the stellar wind  of the normal companion (Illarionov and Sunyaev, 1975[76]).
  2. A shortened duration of the E stage due to the pressure of the accreted plasma which exceeds that of the interstellar medium.
  3. Anisotropy  of the collapse into NS resulting in system disruption, especially in case of wide pairs (Shklovskij, 1976)[180].

A more detailed computation carried out by Lipunov and Prokhorov (1984, 1987)[110, 115], as well as an independent study by Dewey and Cordes (1987)[45], confirmed the original estimate that only about 0.5 percent of the total number of radiopulsars can reside in massive binary systems with optical companions. These calculations took into account such effects as radiowave absorption, radiation delay due to dispersion measure,  and Faraday rotation  in the magnetic field of the stellar wind from the optical companion.

The discovery of such objects gives us a unique possibility to investigate stellar winds from massive stars, a sort of radioprobe launched by nature itself. In this section, we apply the results obtained earlier for the first radiopulsar discovered in a massive binary system (see also Lipunov et al., 1994a[123]).

From the point of view of NS evolution in massive binary systems, identification of the X-ray source Cyg X-3 as a Wolf-Rayet star is of great significance (van Kerkwijk et al., 1992[207]). Most ejectors  in binary systems are not identified as radiopulsars because of absorption in the stellar wind,  but instead, they may appear as sources of high-energy quanta radiated via synchrotron and inverse Compton effects on relativistic particles ejected by the radiopulsar (Lipunov and Prokhorov, 1984;[110] Lipunov and Nazin, 1993, 1994[118, 119]) In this case, as first described by Lipunov (1980)[97], a source of non-thermal radiation in a wide range from radio to hard gamma-ray may appear as a result of a specific reflection effect in the magnetic field of the optical companion.

Cyg X-3 and the periodic radioburster  LSI+61 303 may be examples of just this kind. 

next up previous contents index
Next: The Evolutionary Status of Up: No Title Previous: Massive X-ray Binaries

Mike E. Prokhorov
Sat Feb 22 18:38:13 MSK 1997