The GeV emission of PSR B1259-63 during its last three periastron passages observed by Fermi-LAT

TL;DR

This study analyzes Fermi-LAT observations of PSR B1259-63 during its last three periastron passages, revealing complex gamma-ray flare patterns that challenge existing models of the system's emission mechanisms.

Contribution

It provides a detailed comparison of gamma-ray flare timing and spectral properties across three periastron passages, highlighting new flare behaviors not explained by previous models.

Findings

Multiple flares observed in each periastron passage.

Flare timing and intensity vary between passages.

Detection of a precursor flare in 2017.

Abstract

PSR B1259-63 is a $\gamma$-ray emitting high mass X-ray binary system, in which the compact object is a millisecond pulsar. The system has an orbital period of 1236.7 d and shows peculiar $\gamma$-ray flares when the neutron star moves out of the stellar disk of the companion star. The $\gamma$-ray flare events were firstly discovered by using Fermi-LAT around the 2010 periastron passage, which was repeated for the 2014 and 2017 periastron passages. We analyze the Fermi-LAT data for all the three periastron passages and found that in each flare the energy spectrum can be represented well by a simple power law. The $\gamma$-ray light curves show that in 2010 and 2014 after each periastron there are two main flares, but in 2017 there are four flares including one precursor about 10 d after the periastron passage. The first main flares in 2010 and 2014 are located at around 35 d after the periastron passage, and the main flare in 2014 is delayed by roughly 1.7 d with respect to that in 2010. In the 2017 flare, the source shows a precursor about 10 d after the periastron passage, but the following two flares become weaker and lag behind those in 2010 by roughly 5 d. The strongest flares in 2017 occurred 58 d and 70 d after the periastron passage. These results challenge the previous models.