Fermi Gamma-ray Space Telescope

Periodic Modulation of Fermi 3FGL Sources From Seven Years of LAT Pass 8 Data

R. H. D. Corbet

Abstract:

Fermi LAT Pass 8 data obtained over more than seven years, together with the 3FGL catalog, enable sensitive searches for periodic modulation of LAT light curves. Period searches were made using power spectra of 3,034 light curves with 500s time bins in a range from 1.2 hours up to seven years. To optimize signal-to-noise, light curve generation employed probability weighting, and the power spectra utilized exposure weighting. The power spectra show increased significance of known orbital modulation in the binaries LS 5039, 1FGL J1018.6-5856, and LS I +61 303, and also peaks at the 1667 day superorbital period in LS I 61 303, near the 2450 day orbital period of eta Car, and at the 1237 day orbital period of PSR B1259-63. The new light curves and power spectra also enable a much more sensitive search for binary modulation from so far undiscovered gamma-ray binaries, and can be used to search for long-period modulation in active galactic nuclei, perhaps due to binary supermassive black holes. Because Pass 8 data do not presently come with precomputed diffuse response columns, these have been added to filtered weekly photon files, and are now publicly available from the Fermi Science Support Center.