The long-term X-ray variability of the black hole binary GRS 1915+105

Since the discovering in 1992 August by GRANAT/WATCH, the violent X-ray activity in GRS 1915+105, one of the brightest objects in the X-ray sky even now, have been observed seamlessly over 25 years by multiple X-ray observation instruments. Thanks to its brightness and various observations with the high timing resolution, it has been revealed that the celestial object exhibits 12 characteristic X-ray fluctuations in the time-scale of ∼ sub-second to an hour (Belloni et al. 2000), but few studies about the transition/relationship between the 12 states, or in the other words, the X-ray behavior in much longer time-scale (∼ a month to years), are performed so far.To reveal the comprehensive and global picture of the system, especially the accretion physics under the near- or super-Eddington accretion rate, we performed spectral and timing analysis for the X-ray light curve covering over 20 years obtained by RXTE/ASM and MAXI/GSC. Although the variation in the timescale of sub-second to an hour cannot be fully captured by the all-sky X-ray monitoring instruments, we found that the long-term X-ray variation is possible to be classified to three states based on the hardness-intensity relation, the shape of the spectrum, and the variance in flux, similar to the result shown in Belloni et al. 2000. In this presentation, we show the newly discovered property in the long-term X-ray variation including the classification and then discuss the global dynamics of GRS 1915+105 based on the results.