Low-luminosity observation of BeXRB source IGR J21347$+$4737

Abstract

In this paper, we report the results of the detailed temporal and spectral studies of the BeXRB J21347$+$4737 based on the data from the nuclear spectroscopic telescope array (NuSTAR) and Swift/XRT in a wide energy range of 0.5–50 keV. Coherent pulsation with a period of $322.738\pm 0.018$ s was found in the light curve, implying the source pulsation has spun down by 0.341 s yr$^{-1}$ when compared with the coherent pulsation estimated from XMM Newton >7 years ago. The pulse profile of the source demonstrates energy dependence and has evolved with time. The pulse fraction of the source observed by NuSTAR initially decreases with energy up to $\sim$15 keV, followed by a non-monotonic increasing trend above 15 keV. The source spectrum can be well approximated by an absorbed power-law model with modification by an exponential cutoff at high energies. The absorbed flux of the source is $4\times 10^{-11}$ erg cm$^{-2}$ s$^{-1}$ and its corresponding luminosity is $3.5\times 10^{35}$ erg s$^{-1}$. The study of pulse-phase resolved spectroscopy shows a strong variation of spectral parameters on the phase. No additional emission or absorption features in the form of Fe line or cyclotron lines were observed both in the phase-averaged and phase-resolved spectra of IGR J21347$+$4737.