INTEGRAL/ISGRI post 2024-periastron view of PSR B1259-63

TL;DR

This study analyzes post-periastron INTEGRAL and Swift observations of PSR B1259-63, revealing spectral properties and constraints on emission models in the X-ray to gamma-ray energy range.

Contribution

It provides the first joint spectral analysis of the system in the 0.3-300 keV range after 2024 periastron, constraining spectral curvature and electron energy distributions.

Findings

Spectrum well described by an absorbed power law with photon index 1.42

Constraints on spectral break energy >30 keV and cutoff energy >150 keV

Electron distribution parameters constrained to >0.8 TeV and >1.7 TeV

Abstract

PSR B1259-63/LS 2883 is a well-studied gamma-ray binary hosting a pulsar in a 3.4-year eccentric orbit around a Be-type star. Its non-thermal emission spans from radio to TeV energies, exhibiting a significant increase near the periastron passage. This paper is dedicated to the analysis of INTEGRAL observations of the system following its last periastron passage in June 2024. We aim to study the spectral evolution of this gamma-ray binary in the soft (0.3-10 keV) and hard (30-300 keV) X-ray energy bands. We performed a joint analysis of the data taken by INTEGRAL/ISGRI in July-August 2024 and quasi-simultaneous Swift/XRT observations. The spectrum of the system in the 0.3-300 keV band is well described by an absorbed power law with a photon index of $\Gamma=1.42\pm 0.03$. We place constraints on potential spectral curvature, limiting the break energy $E_\mathrm{b}>30$ keV for $\Delta\Gamma>0.3$ and cutoff energy $E_\mathrm{cutoff}>150$ keV at 95% confidence level. For one-zone leptonic emission models, these values correspond to electron distribution spectral parameters of $E_\mathrm{b,e}>0.8$ TeV and $E_\mathrm{cutoff,e}>1.7$ TeV, consistent with previous constraints derived by H.E.S.S.