Do Gamma-ray Pulsars Mode Change?

From work over the last 20 years, we now know that radio pulsar mode/state changing is the rule rather than the exception, with linked variability in spindown rate and pulse profiles observed from minutes to years. The inevitable conclusion is that these pulsar magnetospheres rapidly reconfigure on these same timescales. By contrast, a lack of variability is almost a defining characteristic of gamma-ray pulsars. More than 300 of these are now known, and one and only one is variable: it, too, has correlated spindown rate and pulse profile changes, proving that the phenomenon is possible. So why are these populations so different? One simple possibility is that any such variability has been too difficult to find, since for many pulsars, the Fermi Large Area Telescope collects just a few photons per day. We present a new method for searching for faint, quasi-periodic mode changing which is sensitive to variability on timescales from about a minute up to years. We calculate the expected sensitivity for every gamma-ray pulsar and we search for variability from the entire population of sufficiently bright pulsars. We present our findings and discuss implications in connection to recent particle-in-cell simulations of mode-changing pulsar magnetospheres.