X-ray observations of PSR B1259-63 near the 2007 periastron passage

TL;DR

This study provides detailed X-ray observations of PSR B1259-63 during its 2007 periastron, revealing spectral evolution and hardening phenomena, but cannot definitively determine the emission mechanism due to lack of TeV data.

Contribution

First detailed spectral evolution analysis of PSR B1259-63 during periastron with multiple X-ray observatories, exploring emission mechanisms and spectral hardening.

Findings

Confirmed pre-periastron spectral hardening with photon index < 1.5

Observed spectral evolution over a 2-month period

Identified possible emission mechanisms but could not conclusively determine the origin

Abstract

PSR B1259-63 is a 48 ms radio pulsar in a highly eccentric 3.4 year orbit with a Be star SS 2883. Unpulsed gamma-ray, X-ray and radio emission components are observed from the binary system. It is likely that the collision of the pulsar wind with the anisotropic wind of the Be star plays a crucial role in the generation of the observed non-thermal emission. The 2007 periastron passage was observed in unprecedented details with Suzaku, Swift, XMM-Newton and Chandra missions. We present here the results of this campaign and compare them with previous observations. With these data we are able, for the first time, to study the details of the spectral evolution of the source over a 2 months period of the passage of the pulsar close to the Be star. New data confirm the pre-periastron spectral hardening, with the photon index reaching a value smaller than 1.5, observed during a local flux minimum. If the observed X-ray emission is due to the inverse Compton (IC) losses of the 10 MeV electrons, then such a hard spectrum can be a result of Coulomb losses, or can be related to the existence of the low-energy cut-off in the electron spectrum. Alternatively, if the X-ray emission is a synchrotron emission of very high energy electrons, the observed hard spectrum can be explained if the high energy electrons are cooled by IC emission in Klein-Nishina regime. Unfortunately the lack of simultaneous data in the TeV energy band prevents us from making a definite conclusion on the nature of the observed spectral hardening and, therefore, on the origin of the X-ray emission.