Temporal variability of the massive X-ray binary 4U 1700-37.

Abstract

Results of a study of the time variability of the X-ray flux from the massive X-ray binary 4U 1700-37/HD 153919 from observations with the EXOSAT satellite are presented. Three types of intensity variations can be distinguished: flaring on time scales of 25 min to 2 h, flickering on time scales equal or less than 10 min with an amplitude equal or less than 10 percent, and sequences of flaring activity lasting between 7 h and 1 d. No periodic modulation could be found for periods between 32 ms and 2h. During states of high luminosity a weak correlation is observed beween spectral hardness and source intensity, which is probably an intrinsic property of the X-ray source. Asymmetries related to the orbital cycle are observed in the shape of the flares as well as in the variability of the hardness ratio. Possible physical processes causing the observed variability and implications for stellar wind models are discussed.