Radio Emission of the Combined Supernova Remnant 3C396 (G39.2-0.3)

Abstract

Using the RT-32 radio telescope of the “Svetloe” IAA RAS observatory in 2017–2018, the flux density measurements of the combined (composite) supernova remnant (SNR) 3С396 (G39.2-0.3) at frequencies of 4840 and 8450 MHz are presented. The data obtained demonstrate source variability. Published data were used to determine the 3C396 flux density in 1962–2008 based on a comparison of the intensities of 3C396 and standard sources. To reduce all the data to a unified system, we used the “artificial moon” (AM) flux scale. A refined spectrum of SNR 3C396 was obtained, which is approximated as the sum of two power-law components with spectral indices α1 = 0.5 and α2 = 0.157. It is assumed that the components of the spectrum are due to emission from the shell and plerion, respectively. The plerion contribution to the SNR’s total flux is estimated: at a wavelength λ = 21 cm, it is close to 30%. Earlier, the contribution estimate was based on X-ray data and did not exceed 4%. The above discrepancy is eliminated if there is a kink in the spectrum of the plerion, similarly to spectra 3C58 and G21.5-0.9. The data obtained during measurements with RT-32 and based on published works show changes in the source flux density on different time scales, from short time intervals (tmin < 0.5 years) or more. The localization and possible causes of detected variability are discussed.