EXOSAT results on the X-ray burster 2S 1254-690.

Abstract

Exosat observations of 2S1254-690 in August 1984 have confirmed the presence of periodic dips in the X-ray intensity. These dips occurred with a period of 3.9 hours and lasted for about 50 minutes. During individual dips, the observed X-ray flux oscillated several times between the quiescent level and an undetectable level on time scales varying from a few seconds to approximately 5 minutes. In addition, a second type-one burst has been observed with characteristics which are very similar to those observed earlier. In this paper, the results of a 20-hour Exosat observation made in August 6th to 7th 1984, are reported and some properties of the dips and of the burst are discussed.