  We confirm a 23 day periodicity during a large flare in 1997 for X-ray data
of X-ray satellite RXTE all sky monitor(ASM), 2 TeV gamma ray data from Utah
Seven Telescope and HEGRA, with a Fourier analysis. We found the three results
to be the same with a newly estimated error. We confirm the presence of a
frequency dependent power (1/f noise) in a frequency-power diagram. Further, we
calculated a chance probability of the occurrence of the 23 day periodicity by
considering the 1/f noise and obtained a chance probability 4.88*10^-3 for the
HEGRA data: this is more significant than previous result by an order. We also
obtained an identical peridoicity with another kind of timing analysis-epoch
folding method for the ASM data and HEGRA data. We strongly suggest an
existence of the periodicity. We divided the HEGRA data into two data sets,
analyzed them with a Fourier method, and found an unstableness of the
periodicity with a 3.4 sigma significance. We also analyzed an energy spectra
of the X-ray data of a RXTE proportional counter array and we found that a
combination of three parameters-a magnetic field, a Lorentz factor, and a
beaming factor-is related to the periodicity.
