Broadband Analysis of the Wind System X1908+075 Based on NuSTAR Data

Abstract

We present the results of our spectral and timing analysis of the X-ray pulsar X1908+075 based on data from the NuSTAR observatory in the wide X-ray energy range 3–79 keV. Along with a detailed analysis of the source’s averaged spectrum, high-precision spectra corresponding to different phases of the neutron star spin cycle have been obtained for the first time. The Comptonization model is shown to describe well the source’s spectrum, and the evolution of its parameters as a function of the pulse phase has been traced. For all spectra (the averaged and phase-resolved ones) in the energy range 5–55 keV we have searched for the cyclotron absorption line. The derived upper limit on the optical depth of the cyclotron line $\tau\sim 0.16$ (1$\sigma$) points to the absence of this feature in the specified energy range, which provides a constraint on the neutron star surface magnetic field: $B<5.6\times 10^{11}$ or >6.2 $\times 10^{12}$ G. For the first time we have analyzed the change in the pulse profile of X1908+075 as the source’s intensity changes. In particular, the main evolution of the pulse profile is shown to occur at energies below 10 keV. At the same time, the observed evolution of the pulse profile points to the presence of several emitting regions.