Abstract
PSR B1259-63 is a γ-ray binary system, where the compact object is a pulsar. The system has an orbital period of 1236.7 days and shows peculiar γ-ray flares (in 100 MeV–300 GeV) after its periastron time. We analyzed the Fermi-LAT observation of PSR B1259-63 during its latest periastron passage, as well as its previous three periastrons. The bright GeV flares started about 60 days after the periastron epoch in 2021. This delay is larger than that around the 2017 periastron and much larger than earlier periastrons. The delay of the GeV flux peak time in each periastron passage is apparent in our results. We discussed the possible origin of this delay and made a prediction of the GeV flux peak time in next periastron passage, based on observation of the previous delays.
Highlights
Gamma-ray binaries are systems composed of a massive star in orbit with a compact object and are characterized by broad non-thermal emission peaking at energies above 1 MeV [1,2]
The pulsar will cross the equatorial disk of the Be type companion twice in one orbit, as the orbital plane of the pulsar is thought to be inclined
The multi-wavelength emission of PSR B1259-63 is usually thought to result from the bow-shaped shock interaction between the relativistic pulsar wind and the stellar wind
Summary
Gamma-ray binaries are systems composed of a massive star in orbit with a compact object and are characterized by broad non-thermal emission peaking (in νFν ) at energies above 1 MeV [1,2]. Was detected by Fermi-LAT around the last four periastron passages, and it shows a very different behavior to the other energy bands. Besides the features in other energy bands, such as the weaker X-ray flux during peaks and the never before observed third X-ray peak, Chernyakova et al [14] confirmed the delay of the GeV flare reported by Chang et al [11] in 2018.
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