Periodicity in the TeV gamma rays and X rays from Markarian 501

Historical TeV gamma-ray flares from Markarian 501 was observed using Utah Seven Telescope Array (7TA) from the end of March to the end of July of 1997. The Rossi X-ray Timing Explorer All Sky Monitor (RXTE ASM) has been observing X rays from Mrk 501 since Jan. 5, 1996. We find evidence for periodicities of $23.9^{+2.3}_{-2.0}$ days and $23.9^{+1.6}_{-2.9}$ days from TeV gamma-ray and X-ray light curves using 7TA and RXTE ASM. Their false-alarm probabilities are $8.2 \times 10^{-3}$ and $5.6 \times 10^{-5}$, respectively.