We report the results of AstroSat and NuSTAR observations of the Be/X-ray binary pulsar SXP 15.3 in the Small Magellanic Cloud during its outburst in late 2017 , when the source reached a luminosity level of \sim 10 ^ { 38 } erg s ^ { -1 } , close to the Eddington limit .
The unprecedented broadband coverage of the source allowed us to perform timing and spectral analysis between 3 and 80 keV .
The pulse profile exhibits a significant energy dependence , and morphs from a double peaked profile to a single broad pulse at energies > 15 keV .
This can be explained by a spectral hardening during an intensity dip seen between the two peaks of the pulse profile .
We detect a Cyclotron Resonance Scattering Feature ( CRSF ) at \sim 5 keV in the X-ray spectrum , independent of the choice of the continuum model .
This indicates a magnetic field strength of 6 \times 10 ^ { 11 } G for the neutron star .