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Considering about seven years of Fermi-Large Area Telescope (LAT) data, wepresent a systematic search for variability possibly related to transitionsbetween states in redbacks and black widow systems. Transitions arecharacterized by sudden and significant changes in the gamma-ray flux thatpersist on a timescale much larger than the orbital period. This phenomenologywas already detected in the case of two redback systems, PSR J1023+0038 and PSRJ1227-4853, for which we present here a dedicated study. We show the existenceof only one transition for each of these systems over the past seven years. Wedetermine their spectra, establishing high-energy cutoffs at a few GeV for thehigh gamma-ray state of PSR J1023+0038 and for both states of PSR J1227-4853.The surveying capability of the Fermi-LAT allows studying whether similarphenomenology has occurred in other sources. Although we have not found anyhint for a state transition for most of the studied pulsars, we note twoblack-widow systems, PSR J2234+0944 and PSR J1446-4701, whose apparentvariability is reminiscent of the transitions in PSR J1023+0038 and PSRJ1227-4853. For the other systems we set limits on potential transitions intheir measured gamma-ray light curves.

Search for transitions between states in redbacks and black widows using seven years of Fermi-LAT observations