Cannot exclude alternative scenarios for production of jet-like structures observed?

What were considered as the alternative theories for something as mysterious as these High Energy Astrophysical Phenomena?

PWNe [Pulsar Wind Nebulae] are nebulae powered by the wind of a pulsar. Pulsar wind is composed of charged particles and when it collides with the pulsar’s surroundings, in particular with the slowly expanding supernova ejecta, it develops a PWN.

Interactions of these nebulae with interstellar medium (ISM) can produce various morphological features, including torus-like structures and bipolar jets.
Observations unveil jet-like structures from the pulsar PSR J1135–6055 | Phys.org

Pulsar wind nebulae (PWNe) produced from supersonic runaway pulsars can render extended X-ray structures in the form of tails and prominent jets. In this Letter we report on the analysis of ∼130 ks observations of the PWN around PSRJ1135-6055 obtained with the Chandra satellite.

The system displays bipolar jet-like structures of uncertain origin, a compact nebula around the pulsar likely formed by the bow shock ahead of it, and a trailing tail produced by the pulsar fast proper motion. The spectral and morphological properties of these structures reveal strong similarities with the PWNe in other runaway pulsars like PSR J1509-5850 and Geminga.

We discuss their physical origin considering both canonical PWN and jet formation models as well as alternative scenarios that can also yield extended jet-like features following the escape of high-energy particles into the ambient magnetic field.
Jet-like structures from PSR J1135-6055

Not plasma cosmology?

Observations show that one small subclass of pulsar wind nebulae, known as supersonically moving PWNe (sPWNe) showcase unusually long X-ray outflows. The length, nearly rectilinear geometry and misaligned orientation (with respect to the pulsar proper motion) of these extended jet-like structures is puzzling, and the origin of such features remains unknown.

“The spectral and morphological properties of the extended structures discussed above cannot exclude alternative scenarios for the production of the jet-like structures observed in PSR J1135–6055,” the authors of the paper wrote.
Observations unveil jet-like structures from the pulsar PSR J1135–6055 | Phys.org