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تسجيل مستخدم جديدTiming and Spectral Studies of the X-ray Pulsar 2S 1417$-$624 During the Outburst in 2021
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We have studied the evolution of different timing and spectral properties of the X-ray pulsar 2S 1417--624 during the recent outburst in January 2021 based on the Neutron Star Interior Composition Explorer (NICER) observations. The spin period during the outburst is $P sim$17.3622 s based on the NICER data and the period decreases slowly with time. The evolution of the spin period and pulsed flux is studied with Fermi/GBM during the outburst and the spin-up rate was found to be varied between $simeq$(0.8--1.8)$times$10$^{-11}$ Hz s$^{-1}$. The pulse profile shows strong energy dependence and variability. The pulse profile shows multiple peaks and dips which evolve significantly with energy. The pulsed fraction shows a positive correlation with energy. The evolution of the spectral state is also studied. The NICER energy spectrum is well described with a composite model of -- power-law and a blackbody emission along with a photo-electric absorption component. An iron emission line is detected near 6.4 keV in the NICER spectrum with an equivalent width of about 0.05 keV. During the recent outburst, the flux was relatively low compared to the 2018 outburst and the mass accretion rate was also low. The mass accretion rate is estimated to be $simeq$1.3 $times$ 10$^{17}$ g s$^{-1}$ near the peak of the outburst. We have found a positive correlation between the pulse frequency derivatives and luminosity. The GL model was applied to estimate the magnetic field in low mass accretion rate and different spin-up rates, which is compared to the earlier estimated magnetic field at a relatively high mass accretion rate. The magnetic field is estimated to be $simeq$10$^{14}$ G from the torque-luminosity model, which is comparatively higher than most of the other Be/XBPs.
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