Periodicity analysis of Markarian 501 flaring activity in 1997

We report on a periodicity analysis of γ-ray observations of very high energy (VHE, E>250 GeV) γ-rays from Markarian 501 (Mrk 501) taken with the Whipple telescope between March and July of 1997. The data correspond to a period of bright flaring of the source, quasi-periodic signals were detected by the Telescope Array Project (TAP) and HEGRA collaboration. Periodic analysis of these data is complicated because the source observations are not continuous and the reported period (≈24 days) is very close to the sampling period. We use the Lomb method, a technique for extracting spectral information from unevenly sampled data, in an attempt to overcome this difficulty. Similar results are shown to exist in data from the strongly correlated X-ray band sampled by the RXTE ASM instrument. No periodicity in the data could be identified with a source frequency.