Multi-wavelength properties of the 2021 periastron passage of PSR B1259-63

TL;DR

This study presents multi-wavelength observations of PSR B1259-63 during its 2021 periastron, revealing unique emission features and delays that suggest a sparser, clumpier stellar disk compared to previous passages.

Contribution

First multi-wavelength campaign during the 2021 periastron, providing new insights into the system's emission behavior and disk structure.

Findings

Delayed GeV flare compared to previous periastrons

Weaker X-ray peaks during disk crossings

Emergence of a new X-ray peak not seen before

Abstract

PSR B1259-63 is a gamma-ray binary system hosting a radio pulsar orbiting around a O9.5Ve star, LS 2883, with a period of ~3.4 years. The interaction of the pulsar wind with the LS 2883 outflow leads to unpulsed broadband emission in the radio, X-ray, GeV, and TeV domains. One of the most unusual features of the system is an outburst at GeV energies around the periastron, during which the energy release substantially exceeds the spin down luminosity under the assumption of the isotropic energy release. In this paper, we present the first results of a recent multi-wavelength campaign (radio, optical, and X-ray bands) accompanied by the analysis of publicly available GeV Fermi/LAT data. The campaign covered a period of more than 100 days around the 2021 periastron and revealed substantial differences from previously observed passages. We report a major delay of the GeV flare, weaker X-ray flux during the peaks, which are typically attributed to the times when the pulsar crosses the disk, and the appearance of a third X-ray peak never observed before. We argue that these features are consistent with the emission cone model of Chernyakova et al (2020) in the case of a sparser and clumpier disk of the Be star.