| We present a scheme to determine the spectral state of the canonical black hole Cyg X-1 using data from previous and current X-ray
all sky monitors (RXTE-ASM, Swift-BAT, MAXI, and Fermi-GBM). State determinations of the hard/intermediate and soft state
agree to better than 10% between di erent monitors, facilitating the determination of the state and its context for any observation of
the source, potentially over the lifetimes of di erent individual monitors. A separation of the hard and the intermediate state, which
strongly di er in their spectral shape and short-term timing behavior, is only possible when monitor data in the soft X-rays (<5 keV)
are available. A statistical analysis of the states confirms the di erent activity patterns of the source (e.g., months to years long
hard state periods or phases during which numerous transitions occurs). It also shows the hard and soft states to be stable, with the
probability of Cyg X-1 remaining in a given state for at least one week to be larger than 85% for the hard state and larger than 75%,
for the soft state. Intermediate states are short lived, with a probability of 50% that the source leaves the intermediate state within
three days. A reliable detection of these potentially short-lived events is only possible with monitor data with a time resolution of
better than 1 d. |
