Is PSR1957 + 20 eclipsed by a comet, magnetosphere or particulate cloud?

The extraordinary eclipsing binary pulsar PSR1957+20 is in eclipse over eight per cent of its orbit. We suggest two explanations for the large eclipse. One possibility is that the companion has a typical white-dwarf magnetic field (∼105 gauss), and that the eclipse is then due to the plasma-filled magnetosphere which is confined and blown back sharply by the pulsar wind. In the other limit of negligible magnetization of the companion, an eclipse could be caused by a particulate cloud (comprising particles of size ∼ 10 cm) which should form about the companion. We assume that the companion is the remnant of an evolved companion star that is now being excited by the 622-Hz pulsar radiation. (author)