2019MNRAS.482.1634S

We report the spectral analysis of accretion powered millisecond X-ray pulsar SAX J1748.9-2021 from the NuSTAR observation made during its 2015 outburst. The spectra displayed a broad emission line at ∼6.5 keV with line width of ∼0.5 keV and excess above ∼20 keV due to Compton hump. The persistent emission of SAX J1748.9-2021 is described by a combination of soft thermal component with kT =0.62^+0.03_–0.05 keV and thermally Comptonized component with kT_e=2.50^+0.06_–0.03 keV reflected from the disc with reflection fraction of 0.30^+0.08_–0.04. We have modelled the reflection spectrum with self-consistent model relxillCP and have found the inclination of the accretion disc to be 32^○_. 3^+4.8_–4.7 and log ξ is equal to 3.05^+0.40_–0.34. We have obtained an upper limit of 57 km for inner disc radius; and the estimated magnetic field strength at the poles is less than 3.4 x 10⁹ G. This kind of detailed investigation of reflection spectrum of SAX J1748.9-2021, especially above 10 keV, has been achieved only because of high statistics NuSTAR data of the source.