A way of examining a hypothetical non--zero γ--ray signal for the time changes is presented. The time variability of the recently observed γ--ray source PKS 2155--304 is discussed. Several measurements were found to be excessive or deficient with large significances on time scales of months and days.
@article{arxiv.1309.6476,
title = {Testing time variability of gamma-ray flux},
author = {Dalibor Nosek and Stanislav Stefanik and Jana Noskova},
journal= {arXiv preprint arXiv:1309.6476},
year = {2013}
}