SIMBAD references

Aims. PSR J0855-4644 is a fast-spinning, energetic pulsar discovered at radio wavelengths near the south-eastern rim of the supernova remnant RX J0852.0-4622. A follow-up XMM-Newton observation revealed the X-ray counterpart of the pulsar and a slightly asymmetric pulsar wind nebula, which suggests possible jet structures. Lying at a distance d≤900pc, PSR J0855-4644 is a pulsar with one of the highest E/d² from which no GeV γ-ray pulsations have been detected. With a dedicated Chandra observation we aim to further resolve the possible jet structures of the nebula and study the pulsar geometry to understand the lack of γ-ray pulsations.
Methods. We performed detailed spatial modelling to constrain the geometry of the pulsar wind nebula and in particular the pulsar line of sight (observer angle) ζ_PSR, which is defined as the angle between the direction of the observer and the pulsar spin axis. We also performed geometric radio and γ-ray light-curve modelling using a hollow-cone radio beam model together with two-pole caustic and outer gap models to further constrain ζ_PSR and the magnetic obliquity α defined as the angle between the magnetic and spin axes of the pulsar.
Results. The Chandra observation reveals that the compact XMM source, thought to be the X-ray pulsar, can be further resolved into a point source surrounded by an elongated axisymmetric nebula with a longitudinal extent of 10''. The pulsar flux represents only ∼1% of the XMM compact source, and its spectrum is well described by a blackbody of temperature kT=0.2keV, while the surrounding nebula has a much harder spectrum (Γ=1.1 for a power-law model). Assuming the origin of the extended emission is a double torus yields ζ_PSR=32.5°±4.3°. The detection of thermal X-rays from the pulsar may point to a low value of |ζ-α| if this emission originates from a heated polar cap. Independent constraints from geometric light-curve modelling yield α≤55° and ζ≤55°, and 10°≤|ζ-α|≤30°. A χ² fit to the radio light curve yields a best fit at (α,ζ_PSR)=(22°,8°), with an alternative fit at (α,ζ_PSR)=(9°,25°) within 3σ. The lack of non-thermal X-ray emission from the pulsar further supports low values for α and ζ under the assumption that X-rays and γ-rays are generated in the same region of the pulsar magnetosphere. Such a geometry would explain, in the standard caustic pulsar model picture, the radio-loud and γ-ray-quiet behaviour of this high E/d² pulsar.