Fermi-LAT Observation of PSR B1259-63 during Its 2021 Periastron Passage

TL;DR

This paper reports on Fermi-LAT observations of PSR B1259-63 during its 2021 periastron, highlighting delayed GeV flares compared to previous periastrons and analyzing their timing and possible origins.

Contribution

It provides the first detailed comparison of GeV flare delays across multiple periastron passages of PSR B1259-63 and predicts future flare timings.

Findings

GeV flares started about 60 days after periastron in 2021

Delay in flare peak time varies across periastrons

Predicted the next flare peak timing based on observed delays

Abstract

PSR B1259-63 is a $\gamma$-ray binary system, where the compact object is a pulsar. The system has an orbital period of 1236.7 days and shows peculiar $\gamma$-ray flares (in 100\,MeV--300\,GeV) after its periastron time. We analyzed the \textit{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.