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

Abstract

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.

arXiv comment10 pages, 8 figures, accepted for publication in A&A

References in corpus (32)

• On the Absorption of X-rays in the Interstellar Medium
• The Nuclear Spectroscopic Telescope Array (NuSTAR) Mission
• Estimating distances from parallaxes IV: Distances to 1.33 billion stars in Gaia Data Release 2
• The Fermi Gamma-Ray Burst Monitor
• Calibration of X-ray absorption in our Galaxy
• Observations of Accreting Pulsars
• The Swift/BAT Hard X-ray Transient Monitor
• Spectral Formation in Accreting X-Ray Pulsars: Bimodal Variation of the Cyclotron Energy with Luminosity
• Cyclotron lines in highly magnetized neutron stars
• The critical accretion luminosity for magnetized neutron stars
• V0332+53 in the outburst of 2004--2005: luminosity dependence of the cyclotron line and pulse profile
• Discovery of a flux-related change of the cyclotron line energy in Her X-1
• Timing Characteristics of the Hard X-ray Emission from Bright X-ray Pulsars Based on INTEGRAL Data
• Completing the puzzle of the 2004-2005 outburst in V0332+53: the brightening phase included
• VLT/UVES spectroscopy of Wray 977, the hypergiant companion to the X-ray pulsar GX301-2
• The variable cyclotron line in GX 301-2
• A Further Study of the Luminosity-Dependent Cyclotron Resonance Energies of the Binary X-ray Pulsar 4U0115+63 with RXTE
• Outburst of GX 304-1 monitored with INTEGRAL: positive correlation between the cyclotron line energy and flux
• Cyclotron Line Variability
• Is there a highly magnetized neutron star in GX 301-2?
• On the magnetic field of the first Galactic ultraluminous X-ray pulsar Swift J0243.6+6124
• Stellar Wind Accretion in GX301-2: Evidence for a High-density Stream
• Broadband spectroscopy using two Suzaku observation of the HMXB GX 301-2
• Multiple cyclotron line-forming regions in GX 301-2
• Orbital Phase Spectroscopy of GX 301--2 with RXTE-PCA
• Variations in the Cyclotron Resonant Scattering Features during 2011 outburst of 4U 0115+63
• Wind Accretion by a Binary Stellar System and Disk Formation
• Stellar wind accretion and accretion disk formation: applications to neutron star high mass X-ray binaries
• Orbital parameters of V 0332+53 from 2015 giant outburst data
• Sub-milliarcsecond Optical Interferometry of the HMXB BP Cru with VLTI/GRAVITY
• Temporal properties of GX 301-2 over a year-long observation with SuperAGILE
• Broadband Observations of the Transient X-ray Pulsar SAX J2103.5+4545

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• Spectral evidence of an accretion disk in wind-fed X-ray pulsar Vela X-1 during an unusual spin-up period
• Catalog of the Galactic population of X-ray pulsars in High-mass X-ray binary systems
• Spin evolution of neutron stars in wind-fed high mass X-ray binaries
• Timing and spectral variability of high mass X-ray pulsar GX 301--2 over orbital phases observed by Insight-HXMT
• Pulse Frequency Fluctuations of Persistent Accretion Powered Pulsars
• X-ray reprocessing in accreting pulsar GX 301-2 observed with Insight-HXMT
• Discovery of a retrogradely rotating neutron star in the X-ray pulsar GX 301$-$2
• An in-depth analysis of the variable cyclotron lines in GX 301$-$2
• On the spin-up events and spin direction of the X-ray pulsar GX 301-2
• Disk vs wind accretion in X-ray pulsar GX 301-2
• Changes in the distribution of circum-binary material around the HMXB GX 301-2 during a rapid spin-up episode of the neutron star
• Clumpy wind studies and the non-detection of cyclotron line in OAO 1657-415
• The FeK$\alpha$ Compton shoulder in accreting Supermassive Black Holes
• On the origin of super-global spin-up trends of X-ray pulsars in HMXB systems