Measuring the Magnetic Field Strength of a Transient X-ray Pulsar 4U 1901+03 by Its Variability on Different Time Scales

: Mereminskiy, I. A.; Semena, A. N.; Lutovinov, A. A.; Tsygankov, S. S.; Molkov, S. V.; Karasev, D. I.

Publisher: Pleiades Publishing Ltd

: NEW YORK

: 2025

: Astronomy Letters / Pis'ma v Astronomicheskii Zhurnal

: Astronomy Letters

: ASTRON LETT+

: 50

: 10

: 600

: 607

: 8

: 1063-7737

: 1562-6873

DOI: https://doi.org/10.1134/S1063773724700506

: https://doi.org/10.1134/s1063773724700506

By combining data from several X-ray telescopes (Swift/XRT, NICER, Chandra) we reconstructed a profile of the 2019 outburst of accreting X-ray pulsar 4U 1901+03 from its peak down to the return to the "low" state. Softening of the X-ray spectrum and disappearance of the pulsations at a later stages of the outburst tentatively indicates that the source transitioned to the "propeller" state at luminosity about 10(36) erg s(-1), which corresponds to a magnetic field strength of B less than or similar to 10(12) G at the neutron star surface. We also investigated the fast X-ray variability that was observed during the peak of 2003 outburst. The shape of the power spectrum could be described with a broken power law, with a break frequency of 7.5 Hz. Assuming that this frequency corresponds to a viscous frequency at a magnetospheric boundary we estimated magnetic field strength as B approximate to 7 x 10(11) G, which is similar to the estimate obtained from observed transition to the "propeller" regime.

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This study was supported by the Ministry of Science and Higher Education of the Russian Federation (grant no. 075-15-2024-647).