Correlations Between the Radio Emission and the X-Ray Timing Properties in GRS 1915+105

GRS 1915+105 is noted for exhibiting X-ray, radio, and infrared emission which is variable on time scales of seconds to minutes (Mirabel et al, 1998; Eikenberry et al, 1998; Greiner et al., 1996; Belloni et al., 1997). However, the source also exhibits steady emission which is reminiscent of black hole candidates such as Cyg X-1 and GX 339-4. Both the variable and steady X-ray conditions can be seen as transitions between two basic modes of X-ray emission (Muno et al, 1999). The soft state exhibits little X-ray emission above 40 keV and no 0.5–10 Hz quasi-periodic oscillation (QPO) in its power density spectrum (PDS). The hard state exhibits a power law energy spectrum up to at least 100 keV, and a 0.5–10 Hz QPO. Bright (100 mJy at 15 GHz), optically thick radio emission often accompanies the hard state of GRS 1915+105 (Foster et al., 1996), similar to the hard states of Cyg X-l (Brocksopp et al., 1999) and GX 339-4 (Corbel et al., 2000). This so-called ‘radio plateau’ emission (e.g. MJD 50730-50750 in Figure 1) originates from a compact jet (Dhawan et al, 2000). However, other hard X-ray states are sometimes accompanied by radio emission which is a factor of 10 fainter (see MJD 50440-50560 and MJD 51053-51096 in Figure 1)—.