| Abstract : | This work reports the discovery of two closely spaced cyclotron resonant scattering features (CRSFs), along with the presence of a narrow Fe Kα emission line at 6.4 keV in the broad-band NuSTAR spectra of transient Be X-ray pulsar GRO J1750–27 obtained during the outburst from 2021 September. The source underwent the fourth outburst, since its discovery in 1995. The NuSTAR observation was performed during the rising phase of the outburst. Pulsations at a period of 4.450710(1) s were observed in the 3–60 keV energy range. The detailed timing analysis reveals that the average pulse profile comprises a broad peak with a weak secondary peak, which evolves with energy. The broad-band phase-averaged spectrum is described by a blackbody, a power law, or a Comptonization component. The two CRSFs are present around 36 and 42 keV in the energy spectrum. These lines indicate a magnetic field with a strength of about 3 . 7 and 4.4 × 10^12 G for the neutron star. The application of the accretion-disc torque models gives an estimated source distance of ~ 13.6–16.4 kpc. |
