We report the results from our analysis of Fermi Large Area Telescope (LAT) data for the transitional millisecond pulsar binary PSR J1023+0038. The time period of the data is nearly 9 yr, and that after the source’s transition, in June 2013 from the disk-free state to the active state of having an accretion disk, is approximately 4 yr. We identify a high-energy >5.5 GeV component in the source’s spectrum in the active state, and find this component is only significantly detected in half of the orbital phase centered at the descending node (when the pulsar is moving towards the Earth). Considering the pulsar scenario proposed for multi-frequency emission from the source, in which the pulsar is still active and a cold-relativistic pulsar wind inverse-Compton scatters the photons from the accretion disk, we discuss the origin of the high-energy component. In order to explain the observed spectrum, a power-law distribution of particles, with an index of ∼3, in the pulsar wind is required, while the orbital variations are possibly due to changes in power-law index as a function of orbital phase.
gamma rays: stars, (stars:) binaries: eclipsing, stars: neutron
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