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We report the spectral analysis of accretion powered millisecond X-ray pulsarSAX J1748.9-2021 from the NuSTAR observation made during its 2015 outburst. Thespectra displayed a broad emission line at $\sim 6.5$ keV with line width of$\sim 0.5$ keV and excess above $\sim 20$ keV due to Compton hump. Thepersistent emission of SAX J1748.9-2021 is described by a combination of softthermal component with $kT =0.62^{+0.03}_{-0.05}$ keV and thermally Comptonizedcomponent with $kT_e=2.50^{+0.06}_{-0.03}$ keV reflected from the disc withreflection fraction of $0.30^{+0.08}_{-0.04}$. We have modeled the reflectionspectrum with self-consistent model relxillCP and have found the inclination ofthe accretion disc to be $32.3^{^\circ +4.8}_{-4.7}$ and log $\xi$ is equal to$3.05^{+0.40}_{-0.34}$. We have obtained an upper limit of 57 km for inner discradius; and the estimated magnetic field strength at the poles is less than$3.4 \times 10^9$ G. This kind of detailed investigation of reflection spectrumof SAX J1748.9-2021, especially above 10 keV, has been achieved only because ofhigh statistics NuSTAR data of the source.

Study of the reflection spectra of SAX J1748.9-2021