Nustar observation of the binary system 4U 0114 + 65

Abstract

ABSTRACT The high-mass X-ray binary system 4U 0114 + 65 was observed by Nustar in October 2019 and by XMM-Newton in August 2015. Here we performed spectral and timing analysis of the Nustar observation and carry out timing analysis on the XMM-Newton data. We measured the spin period of the neutron star from both observations and found a spin-up rate $\dot{p}$ = 1.54 ± 0.38 × 10−6$\mathrm{s\, s}^{-1}$ . During the Nustar observation, two flares occurred, one shortly after the start of the observation and the other near the end separated by a long period of low/quiescent state. The large and sudden flares mostly resulted from accretion of corotating interaction region (CIR) material. A common spectral model to high mass X-ray binaries (HMXBs), powerlaw with high energy cutoff and absorption at low energy, gave a good fit to both flaring and quiescent states. A fluorescent iron line was not required in fitting any of the states. On the other hand, very tentative evidence of Cyclotron Resonant Scattering Feature (CRSF) at ∼17 keV was found during fitting using cyclabs model; however, fitting improvement was not significant enough to confirm its detection, plus a very narrow width (<1 keV) was obtained for the line and its first harmonic. Visual inspection of the spectra showed a deficiency of emission near the expected first and second harmonic. Another important feature visually noticed in the spectra is the presence of hard tail above 50 keV. This could be explained by the shocked material bounding the CIR.