  In this work we investigate broad band (1-79 keV) spectral nature of the
atoll source 4U 1636-536 using the combined Nu-STAR and SWIFT-XRT data. The
spectra are complex and have emission components from the disc, boundary-layer
and corona. In addition to that a broad iron line is also observed. A
relativistic line model assuming Schwarzchild metric fits this feature. The
total flux varies from 1.4 $\times$ 10$^{-9}$ to 4.36 $\times$ 10$^{-9}$
$ergs/s/cm^2$. At the highest flux level the source was found in the soft
state. In this state the Comptonized component has temperature $kT_e \sim 3$
keV and optical depth $\tau \sim $ 16. We also detect a non-thermal tail with
index $\sim$ 2.4, contributing $\sim$ 10 \% of the total flux in the soft
state. We also find that the inner disc radius, electron temperature and
optical depth vary with the total 0.1-100 keV unabsorbed flux. We discuss the
implication of the results in this paper.
