On the nature of the X-ray pulsar XTE J1859+083 and its broad-band properties

ABSTRACT This work is devoted to the study of broad-band 0.8–79 keV spectral and timing properties poorly studied X-ray pulsar XTE J1859+083 during its 2015 outburst based on data from NuSTAR Swift observatories. We show that source pulse profile has complex shape depends energy band. Pulse fraction constant value around 35 per cent in broad band, this behaviour atypical for pulsars. At same time spectrum typical class objects a power-law with an exponential cutoff at high energies. No cyclotron absorption line was discovered spectrum. On basis indirect method absence line, estimation made magnetic field strength as less than 5 × 1011 G or belonging interval 1012 $2.0^{+0.9}_{-1.2}\times 10^{13}$ G. Data NOT SALT telescopes well optical IR sky surveys allowed us also nature companion. have proposed new possible candidates companion most likely candidate identified. The results photometry spectroscopy these companions showed system Be binary, showing Brγ, He i, strong H α lines.