TOO: THE NATURE OF THE SUPERLUMINAL GALACTIC SOURCE GRS 1915+105 ISO MONITORING OF THE MOST POWERFUL SOURCE IN THE GALAXY

grs 1915+105 was discovered in aug 1992 with the watch allsky xray monitor on board the granat satellite. the source has been since then one of the brightest objects in the xray sky, highly variable in all wavelenghts, from gammarays to radio. at a distance of 12 kpc, the absorption towards the source is almost 30 magnitudes, putting the object well beyond the reach of optical telescopes. the uniqueness of grs 1915+105 is that it shows superluminal motion, following a bright radio outburst seen in march 1994 the first such case in our galaxy. grs 1915+105 is a binary system in which a massive black hole (with perhaps 33 solar mases) is accreting mass from a nearby companion. the companion class is still unclear, but it could be a highmass object, on the basis of observations performed in aug 1995, that revealed the nearir reverberation of an energetic radiooutburst. the jet was also observed in the kband in july 1995. nearir spectroscopy indicates the presence of strong emission lines (he i 2.06 um and brgamma 2.16 um) during the high activity periods. grs 1915+105 underwent a new strong outburst in xrays and radio frequencies in late october 1997. ejection of plasmoids at 0.92 c was also observed at merlin in the radio domain. iso observations, following the too, indicated that the source varies by a factor of 30 (0.515 mjy) in the lw3 band on a several day timescale. at that time, when the source displayed a strong xray and radio activity, the source flux was much fainter than seen previous ly at 10 um (what is certainly surprising does not have a good s/n ratio. therefore, and taking into account the strong 10um variability seen in grs 1915+105, which appears not to follow the nearir or radio behaviour, we request further monitoring of the source during the last iso observing window (9/36/5), beginning on march 16 (rev. 852, not scheduled yet). truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]