Malacaria, C.Kretschmar, P.Madsen, KristinWilson-Hodge, C. A.Coley, Joel B.Jenke, P.Lutovinov, Alexander A.Pottschmidt, KatjaTsygankov, Sergey S.Wilms, J.2022-08-152022-08-152021-03-15Malacaria, C. et al. “The X-Ray Pulsar XTE J1858+034 Observed with NuSTAR and Fermi/GBM: Spectral and Timing Characterization plus a Cyclotron Line”, The Astrophysical Journal, vol. 909, no. 2, 2021. doi:10.3847/1538-4357/abddbc.https://doi.org/10.3847/1538-4357/abddbchttp://hdl.handle.net/11603/25412Accreting X-ray pulsars (XRPs) undergo luminous X-ray outbursts during which the spectral and timing behavior of the neutron star can be studied in detail. We analyze a NuSTAR observation of the XRP XTE J1858+034 during its outburst in 2019. The spectrum is fit with a phenomenological, a semiempirical, and a physical spectral model. A candidate cyclotron line is found at 48 keV, implying a magnetic field of 5.4 × 1012 G at the site of emission. This is also supported by the physical best-fit model. We propose an orbital period of about 81 days based on the visual inspection of the X-ray outburst recurrence time. Based on Fermi/GBM data, the standard disk accretion-torque theory allowed us to infer a distance of 10.9 ± 1.0 kpc. Pulse profiles are single-peaked and show a pulsed fraction that is strongly energy-dependent at least up to 40 keV.7 pagesen-USThis work was written as part of one of the author's official duties as an Employee of the United States Government and is therefore a work of the United States Government. In accordance with 17 U.S.C. 105, no copyright protection is available for such works under U.S. Law.Public Domain Mark 1.0Text