NuSTAR observations of the wind-fed X-ray pulsar GX 301--2 during an unusual spin-up event

• Main Authors: Nabizadeh, Armin, Mönkkönen, Juhani, Tsygankov, Sergey S, Doroshenko, Victor, Molkov, Sergey V, Poutanen, Juri
• Format: Journal Article
• Language: English
• Published: 30-07-2019
• Subjects: Physics - High Energy Astrophysical Phenomena
• DOI: 10.48550/arxiv.1907.12923

A&A 629, A101 (2019) We report on \textit{NuSTAR} observations of the well-known wind-accreting
X-ray pulsar \source\ during a strong spin-up episode that took place in
January-March 2019. A high luminosity of the source in a most recent
observation allowed us to detect a positive correlation of the cyclotron line
energy with luminosity. Beyond that, only minor differences in spectral and
temporal properties of the source during the spin-up, presumably associated
with the formation of a transient accretion disk, and the normal wind-fed state
could be detected. We finally discuss conditions for the formation of the disk
and possible reasons for lack of any appreciable variations in most of the
observed source properties induced by the change of the accretion mechanism,
and conclude that the bulk of the observed X-ray emission is still likely
powered by direct accretion from the wind.