GRS 1915+105

GRS 1915+105 was discovered by WATCH in 1992. ROSAT pointed observations and BATSE monitoring have revealed this source to be remarkably different from known low-mass X-ray binaries (LMXB) or transient X-ray sources. The peculiar lightcurve and the steep spectrum up to 200 keV argue against a LMXB. The lack of any systematic brightness decline, of any optical brightening and of periodic pulsations argues against known types of transients. We propose to observe this peculiar source in order to study in detail the spectral shape of the continuum emission, the presence and relative flux ratios of spectral lines, and the possible spectral variability during the drastic day-to-day flux variations (up to a factor of 5).