AstroSat and Insight-HXMT observations of the long-period X-ray pulsar 4U 2206+54

We report the timing and spectral studies of the accreting X-ray pulsar 4U 2206+54 using astrosat and hxmt observations taken in 2016 and 2020 respectively. X-ray pulsations from the system are detected by both missions. The astrosat discovered a significant periodic signal at ~ 5619 s in 2016 and hxmt found a pulsation period at ~ 5291 s in 2020. A comparison of its spin-period evolution with the present spin-period estimates shows that the neutron star in 4U 2206+54 now has recently undergoing a spin-up episode after attaining to its slow pulsations of ~5750~s around 2015 from its prolonged spin-down phase. The present average spin-up rate of the pulsar is found to be at ~1.2×10⁻¹³ Hz~s⁻¹. The phase-averaged spectra of the pulsar in 1-60 could be explained with a high energy cutoff power-law continuum model, no evident line features are found with astrosat. The application of Comptonization models such as comptt and compmag to the phase averaged spectra of 4U 2206+54 reveal a hotter source photon region near the pulsar with an emission size extending to ~ 2-2.8~km. Using the quasi-spherical settling accretion theory, we explain the present spin-up and the possibility of strong magnetic field of the pulsar.