FAST Continuum Mapping of the SNR VRO 42.05.01

Abstract

The relativistic electrons rotate in the enhanced magnetic field of the supernova remnants and emit the synchrotron radio emission. We aim to use the Five-hundred-meter Aperture Spherical radio Telescope (FAST) to obtain a sensitive continuum map of the supernova remnant VRO 42.05.01 (G166.0+4.3) at 1240 MHz. The 500 MHz bandwidth is divided into low and high-frequency bands centered at 1085 and 1383 MHz to investigate the spectral index variations within the remnant, together with the Effelsberg 2695 MHz data. We obtained an integrated flux density of 6.2 ± 0.4 Jy at 1240 MHz for VRO 42.05.01, consistent with previous results. The spectral index found from temperature-temperature plot (TT-plot) between 1240 and 2695 MHz agrees with previous values from 408 MHz up to 5 GHz. The three-band spectral index distribution shows a clear flatter value of α ∼ −0.33 in the shell region and steeper index of α = −0.36 to −0.54 in the wing region. The flatter spectral index in the shell region could be attributed to a second-order Fermi process in the turbulent medium in the vicinity of the shock and/or a higher compression ratio of shock and a high post-shock density than that in elsewhere.