Multi-wavelength observations of bow-shock pulsar wind nebulae

Abstract

A bow-shock pulsar wind nebula (BSPWN) is a synchrotron bubble, formed when the relativistic outflow of a fast-moving pulsar is confined by the ambient environment. BSPWNe are powerful particle acceleration sites nearby in the Universe, thus providing an ideal testing ground for the particle acceleration theories in the relativistic regime. In particular, unlike PWNe in early stage, BSPWNe formation does not involve their parent supernova remnants, so their structures are steady. This hence allows simple modeling. I studied spectral energy distributions of four BWPWNe, namely, PWN B0355+54 (the Mushroom Nebula), PWN J0357+3205, PWN J1740+1000, and the Mouse Nebula (G359.23−0.82). For the first three PWNe, deep Very Large Array (VLA) radio searches using the D configuration at 3GHz were carried out. However, no extended emission was detected. I reported a 3σ flux density limit and use them as constraints in multi-wavelength modeling to probe the injected particle distribution from shocks. The limits are 0.24, 0.041 and 0.093mJy for PWN B0355+54, PWN J0357+3205, and PWN J1740+1000, respectively. The Mouse Nebula (G359.23-0.82) is a prototypical BSPWN and are bright in both radio and X-ray. Its multi-wavelength properties are beneficial to spectral modeling. I constructed a multi-wavelength spectrum of the Mouse Nebula, using the radio, infrared, X-ray, and gamma-ray Fermi data. I developed a one- zone static model to infer and compare three injected particle distributions predicted from the theories, namely, a single power law, a broken power law, and a Maxwellian distribution with a high-energy power-law tail, based on the multi-wavelength spectrum of the Mouse Nebula. I considered the combined effects of synchrotron radiation, synchrotron cooling, as well as inverse-Compton scattering in the model. The results favor a broken power law and a Maxwellian distribution with a high-energy power-law tail injected spectra than a single power law, implying that simple predictions from conventional Fermi acceleration theory cannot explain the observations of the Mouse Nebula. In addition, it needs observations using high-frequency radio telescopes, e.g. ALMA, and infra-red telescopes to provide complete coverage for better modeling and further statistical tests to identify the best-fit inferred injected particle distribution, and therefore the most favorable particle acceleration theory.