Long-term X-ray Variability and the Importance of the ASM

From determining the log(N)-log(S) distribution of XRBs in the Milky Way, to testing radio/X-ray correlations of microquasars and BHCs, studying long term variability, and acting as a trigger for observations of transient sources, the ASM on RXTE has proved an invaluable resource. I will briefly discuss some highlights of the many results that have been possible only because of the ASM. The fact that the number of papers per year (over 100) that have relied on ASM data has remained steady over the 8-year lifetime of the RXTE is an indication of the enduring usefulness of all-sky X-ray monitoring. I argue that the permanent presence in space of an ASM-like instrument is a major benefit to numerous active branches of astrophysics, that there is no substitute (ground-based or in other parts of the electromagnetic spectrum) for this capability, and that the planning process for future missions ought to take into account the ongoing scientific need for all-sky X-ray monitoring