  We studied the long term flux distribution of Cygnus X-1 using RXTE-ASM
lightcurves in two energy bands B (3-5 keV) & C (5-12.1 keV) as well as MAXI
lightcurves in energy bands B (4-10 keV) & C (10-20 keV). The flux histograms
were fitted using a two component model. For MAXI data, each of the components
is better fitted by a log-normal distribution, rather than a Gaussian one.
Their best fit centroids and fraction of time the source spends being in that
component are consistent with those of the Hard and Soft spectral states Thus,
the long term flux distribution of the states of Cygnus X-1 have a log-normal
nature which is the same as that found earlier for much shorter time-scales.
For RXTE-ASM data, one component corresponding approximately to the Hard state
is better represented by a log-normal but for the other one a Gaussian is
preferred and whose centroid is not consistent with the Soft state.This
discrepancy, could be due to the larger fraction of the Intermediate state
(~11.25%) in the RXTE-ASM data as compared to the MAXI one (~4%). Fitting the
flux distribution with three components did not provide an improvement for
either RXTE-ASM or MAXI data, suggesting that the data corresponding to the
Intermediate state may not represent a separate spectral state, but rather
represent transitions between the two states.
