is shown in the left-hand panel of Figure \[image\_p4tbsins\_nosmt\]. The sky specific intensity can be related to ${\delta T_{\rm b}}$ as $$I_{\nu}(\vec{\theta}) = \frac{2 k_B \nu^2  }{c^2} {\delta T_{\rm b}}(\vec{\theta}, \nu),
\label{inten}$$ where $k_B$ is Boltzmann constant and $c$ is the speed of light. The flux per synthesized beam can be obtained by, $$S_{\nu} =I_{\nu}(\vec{\theta}) \times \Delta \Omega,
\label{flux_beam}$$ where $\Delta \Omega = (\Delta \theta)^2$ is the beam solid angle. The quantity $S_{\nu}$ thus gives the total flux within a single beam. The middle panel of Figure \[image\_p4tbsins\_nosmt\] shows $S_{\nu}$ distribution along the angular directions for our fiducial source for an angular resolution (or beam) 2 at the central frequency channel (which contains the centre of the source in this case). Although the angular extents of our original image are $6.7^{\circ}\times6.7^{\circ}$, we show only a smaller $3.4^{\circ}\times3.4^{\circ}$ image. The maximum amplitude of the signal $S_{\nu}$ in the map is $\sim -13 ~\mu$Jy, with the negative sign signifying that the signal is in absorption.

![image](p4tbsins_nosmt1.eps)

Noise maps {#noi_map}
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The system noise $N(\vec{U}, \nu)$ at different baselines and frequency channels are uncorrelated and expected to be Gaussian random variables with zero mean. The rms noise for each baseline and frequency channel 