We report on a likelihood stacking search for gamma-ray pulsars at 525 high latitude locations that coincide with known radio pulsar positions. We report 8 newly detected or associated pulsar candidates and 36 sub-threshold pulsar candidates. Stacking their likelihood profiles in spectral parameter space implies a pulsar-like spectral index and a flux one order of magnitude below the Fermi sensitivity. The same procedures performed on empty control fields imply a high false detection rate (20-50%) although the stacked spectra are distinctly softer than the pulsars. This study also probes a unique region of parameter space populated by older, transitional, and recycled (millisecond) pulsars. Many of these sources have lower rotational energy loss rates implying that the empirical γ-ray "death line" could be predominantly a sensitivity limit. Their luminosities, however, are consistent with the heuristic relation between spin-down power and γ-ray luminosity. If their pulsar nature can be confirmed, these results will expand the number of γ-ray pulsars by 16%. Furthermore, the improved millisecond pulsar luminosity function with these new sources can help characterize their possible contribution to the Galactic center GeV excess.
We report on a likelihood stacking search for gamma-ray pulsars at 362 high-latitude locations that coincide with known radio pulsar positions. We observe a stacked signal conservatively 2.5σ over the background. Stacking their likelihood profiles in spectral parameter space implies a pulsar-like spectral index and a characteristic flux a factor of 2 below the Fermi-LAT point source sensitivity, assuming isotropic/unbeamed emission from all sample pulsars. The same procedures performed on empty control fields indicate that the pulsars as a population can be distinguished from the background with a Δ(TS) = 28 at the peak location (or 4.8σ), and the stacked spectra of the control fields are distinctly softer than those of the pulsars. This study also probes a unique region of parameter space populated by low $\dot{E}$ pulsars, most of which have no γ-ray ephemeris available, and is sensitive to high duty cycles. We also discusses the possible γ-ray emission mechanism from such pulsars.
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