Magnetic field properties of the SNR HB 9

Abstract

We aim to study the polarization and magnetic field properties of the SNR HB 9 using new 21-cm continuum cube data from the Five-hundred-meter Aperture Spherical radio telescope (FAST). We computed the Faraday depth at 21 cm, and re-analyzed the rotation measures (RMs) of HB 9 using in addition Effelsberg 2695-MHz and Urumqi 4800-MHz polarization data. FAST total-intensity images of two subbands are decomposed into components of multiple angular scales to check spectral-index variation via temperature versus temperature plots (TT-plots). The filamentary emission has a spectral index ($S\sim {\nu }^{\alpha }$) of $\alpha =-$0.52, corresponding to freshly accelerated relativistic electrons. The diffuse emission has a steeper spectrum of $\alpha =-$0.63, corresponding to confined electrons that are no longer accelerated. The FAST detected 1385-MHz polarized emission might come from a thin layer in the outer envelope of the shells, with a Faraday depth of 4-28 rad m${}^{-2}$ from the Faraday rotation synthesis result. The RMs derived from the Effelsberg 2695-MHz and Urumqi 4800-MHz polarization data show about 70 rad m${}^{-2}$ in the eastern and northern shell, and 124 rad m${}^{-2}$ in the inner and southern patches. The regular magnetic field is about 5$-$8 $\mu$G over the remnant. The northern shell shows depolarization at 2695 MHz relative to the 4800-MHz polarization data, indicating an additional random magnetic field of 12 $\mu$G on the scale of 0.6 pc. The shock wave might have entered the dense gas environment in the northern-shell region and has driven turbulence to cause depolarization at 2695 MHz.

9 pages,8 figures, accepted in A&A

References in corpus (11)

• Radio Spectrum and Distance of the SNR HB9
• Fermi LAT Observation of Supernova Remnant HB9
• Turbulence and Particle Acceleration in Radiative Shock Waves in the Cygnus Loop II: Development of Postshock Turbulence
• Multi-scale decomposition of astronomical maps -- a constrained diffusion method
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• Distance of PSR B0458+46 indicated by FAST HI absorption observations
• Detection of gamma rays around SNR HB9 and its implication to the diffusive shock-acceleration history
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• Optical observations of the Galactic SNR HB9 and H II region G159.2+3.3
• Long, depolarising H$\alpha$-filament towards the Monogem ring