![ghostnote dokara ghostnote dokara](https://t.facdn.net/35085943@600-1581971632.jpg)
Note that strong point sources have been removed before TT- plots were made. For the spectral index between our 4800 MHz data and the 865 MHz data, we smoothed the 4800 MHz data to a HPBW of 14. We convolved all data to a common HPBW of 10 ′ except for the 865 MHz data and then obtained the spectral indices β and α listed in Table 3. The published 865 MHz data around SNRs G127.1 + 0.5 and G126.2 + 1.6 by Reich, Zhang & Fürst (2003) were also used. We retrieved the CGPS 1420 MHz and 408 MHz survey data 2, which includes E ff elsberg data for a correct representation of the large-scale emission, and also the E ff elsberg 1408 MHz survey data separately 3. Fortunately many survey data are public and thus facil- itates the study of TT-plots. The flux density and brightness temperature are related via S ν ∝ ν 2 T ν, so the spectral index for brightness temperatures can be translated to the spectral index for flux densities as α = β + 2. Therefore, we also obtained the spectral index for the brightness temperature β via temperature-temperature plots (TT- plots), which are una ff ected by the uncertainty of the background level. For example, a background level uncertainty of 10% at 4.8 GHz can introduce an error of about − 0.1 for the spectral index between 4.8 GHz and 1.4 GHz. However, the spectral index could be influenced by the uncertainty of the background level. The spectral index can be obtained by fitting a power-law to the integrated flux densities observed at various frequencies. The uncertainty of the background level and the source contribution together introduce a typical error of less than 10% of the flux density of an object. 8 ( S ν ∝ ν α with S ν being the flux density at a frequency ν ) to yield the source contribution. The total flux density of these sources is then extrapolated to the frequency of 4.8 GHz from 1.4 GHz with a spectral index of α = − 0.
![ghostnote dokara ghostnote dokara](https://i.pinimg.com/736x/8b/11/30/8b11303d8d859552cde4436c410afc2e.jpg)
In order to figure out the contribution from compact sources, we extracted all point sources towards the target object from the NVSS source catalog (Condon et al. Then a ”twisted” hyper-plane fitted by using the pixel values surrounding the source is subtracted. The filtering beam was taken to be 33 ′ × 33 ′, which gives roughly the scale length of the separation between large-scale and small-scale emission. In this paper, the “background filter- ing” technique developed by Sofue & Reich (1979) is applied to subtract the large-scale di ff use emission. achieve an integrated net flux density of an extended source the contributions of the di ff use background and extragalactic sources must be removed.