0420083

We propose to study the pre-periastron flare of GX 301-2 by observingfour pre-periastron flares resulting in a total observation time of600 ksec. This will allow us to study the structure (includingdensity and clumpiness) of the gas stream flowing from Wray 977 to GX 301-2which is intercepted by the neutron star prior to periastron passagegiving rise to the pre-periastron flare. As the source is verybright during the flare spectra with high statistical quality up to100 keV will be obtained. These will then be used for phaseresolved spectroscopy to study the spectral variation (esp. thecyclotron line) with pulse phase and to search for a harmonicline. The obtained flare data will be complemented by substantialarchival data taken outside the flare for comparison. Such a studyis not possible with archival data as there is almost no coverage of the pre-periastron flare. [truncated! Please see actual data for full text]