X-Ray Pulsar XTE J1858+034: Discovery of the Cyclotron Line and the Revised Optical Identification
Kretschmar, Peter; Doroshenko, Victor; Tsygankov, Sergey S.; Mushtukov, Alexander A.; Lutovinov, Alexander A.; Poutanen, Juri; Molkov, Sergey V.; Malacaria, Christian; Djupvik, Anlaug A.; Karasev, Dmitri I.
Finland, Russia, Spain, Denmark, Germany, Netherlands, United States, Sweden
Abstract
We present the results of a detailed investigation of the poorly studied X-ray pulsar (XRP) XTE J1858+034 based on the data obtained with the NuSTAR observatory during the outburst of the source in 2019. The spectral analysis resulted in the discovery of a cyclotron absorption feature in the source spectrum at ∼48 keV in both the pulse phase-averaged and resolved spectra. Accurate X-ray localization of the source using the NuSTAR and Chandra observatories allowed us to accurately determine the position of the X-ray source and identify the optical companion of the pulsar. The analysis of the counterpart properties suggested that the system is likely a symbiotic binary hosting an XRP and a late-type companion star of the K-M classes rather than a Be X-ray binary as previously suggested.