GINGA OBSERVATIONS OF GX-3- LONG-TERM VARIABILITIES, BRANCHES, AND X-RAY-BURSTS(1 )

The bright Galactic bulge source GX 3+1 (4U 1744-26) was observed with the Ginga satellite on several occasions from 1987 through 1990. The source has been found to show flux variations of a factor of 2 on the time scales of years. The hardness ratio, which is a measure of the sp ect;al shape, stayed almost constant during the variations. Two type-I X-ray bursts were detected near to the lower end of the hu( variation s. When the variabilities were investigated on a shorter time scale of days, upper and lower banana branches were found to clearly appear in the hardness-intensity diagram. The branches become smeared out if da ta are accumulated for much longer than a few days in the hardness-int ensity diagram. As. indicated by the presence of a banana branch, the short-term variations are correlated variations between the intensity and the hardness and, hence, their nature is very different from that of the long-term variations. This means that the long- and short-term variations have different origins. If the burst detection with Hakucho and Ginga in a low state reflects a red change in the mass accretion rate, the long-term variations may be determined by changes in the mas s accretion rate. This would lead to the conclusion that the change in the mass accretion rate may not be responsible for the formation of t he banana branches. We also discuss another possible interpretation th at the mass accretion rate determines the branches, not the long-term variations.