A time-differencing technique for detecting radio-quiet gamma-ray pulsars

Detecting periodicity from a gamma-ray pulsar is exceedingly difficult without prior knowledge of its pulsation frequency and frequency derivative. The low fluxes attainable in the gamma-ray band mandate very long exposures, making the direct application of Fourier analysis methods computationally prohibitive. Accumulation of phase shifts induced by significant frequency derivatives requires that the large Fourier transforms be repeated over many trials, and occasional "glitches" in the pulsar rotation compound the difficulties. By analyzing the differences of photon arrival times rather than the time series itself, we show that we can maintain good sensitivity while greatly reducing the effects of frequency derivatives and glitches. To demonstrate its power, we use simulated data to compare our time-differencing algorithm with two Fourier methods used in previous searches for radio-quiet gamma-ray pulsars.