Patterns of variability in Be/X-ray pulsars during giant outbursts

Abstract

The discovery of source states in the X-ray emission of black-hole binaries and neutron-star low-mass X-ray binaries constituted a major step forward in the understanding of the physics of accretion onto compact objects. While there are numerous studies on the correlated timing and spectral variability of these systems, very little work has been done on high-mass X-ray binaries, the third major type of X-ray binaries. The main goal of this work is to investigate whether Be accreting X-ray pulsars display source states and characterise those states through their spectral and timing properties. We have made a systematic study of the power spectra, energy spectra and X-ray hardness-intensity diagrams of nine Be/X-ray pulsars. The evolution of the timing and spectral parameters were monitored through changes over two orders of magnitude in luminosity. We find that Be/X-ray pulsars trace two different branches in the hardness-intensity diagram: the horizontal branch corresponds to a low-intensity state of the source and it is characterised by fast colour and spectral changes and high X-ray variability. The diagonal branch is a high-intensity state that emerges when the X-ray luminosity exceeds a critical limit. The photon index anticorrelates with X-ray flux in the horizontal branch but correlates with it in the diagonal branch. The correlation between QPO frequency and X-ray flux reported in some pulsars is also observed if the peak frequency of the broad-band noise that accounts for the aperiodic variability is used. The two branches may reflect two different accretion modes, depending on whether the luminosity of the source is above or below a critical value. This critical luminosity is mainly determined by the magnetic field strength, hence it differs for different sources.

Complete missing words in title. Proof corrections added

References in corpus (66)

• Modelling the behaviour of accretion flows in X-ray binaries
• First Results from the All-Sky Monitor on the Rossi X-ray Timing Explorer
• Be/X-ray binaries
• A Unified Description of the Timing Features of Accreting X-ray Binaries
• RXTE Observation of Cygnus X-1: II. Timing Analysis
• The evolution of black hole states
• Magnetic Fields of Accreting X-Ray Pulsars with the Rossi X-Ray Timing Explorer
• In-flight Performance of the High Energy X-ray Timing Experiment on the Rossi X-ray Timing Explorer
• A natural explanation for periodic X-ray outbursts in Be/X-ray binaries
• Soft state of Cygnus X-1: stable disk and unstable corona
• A Global Spectral Study of Black Hole X-ray Binaries
• Thermal and Bulk Comptonization in Accretion-Powered X-Ray Pulsars
• Spectral Formation in Accreting X-Ray Pulsars: Bimodal Variation of the Cyclotron Energy with Luminosity
• Long Term Variability of Cyg X-1 I. X-ray spectral-temporal correlations in the hard state
• Evaluating Spectral Models and the X-ray States of Neutron-Star X-ray Transients
• Viscous Effects on the Interaction between the Coplanar Decretion Disc and the Neutron Star in Be/X-Ray Binaries
• Discovery of a flux-related change of the cyclotron line energy in Her X-1
• A transient radio jet in an erupting dwarf nova
• How Do Z and Atoll X-ray Binaries Differ?
• Completing the puzzle of the 2004-2005 outburst in V0332+53: the brightening phase included
• Study of the accreting pulsar 4U 0115+634 with a bulk and thermal Comptonization model
• Discovery of a Third Harmonic Cyclotron Resonance Scattering Feature in the X-ray Spectrum of 4U 0115+63
• The Be/X-ray Transient V0332+53: Evidence for a tilt between the orbit and the equatorial plane?
• A Further Study of the Luminosity-Dependent Cyclotron Resonance Energies of the Binary X-ray Pulsar 4U0115+63 with RXTE
• No anti-correlation between cyclotron line energy and X-ray flux in 4U 0115+634
• A Decade in the Life of EXO 2030+375: A Multi-wavelength Study of an Accreting X-ray Pulsar
• Pulse-amplitude-resolved spectroscopy of bright accreting pulsars: indication of two accretion regimes
• A 0535+26 in the August/September 2005 outburst observed by RXTE and INTEGRAL
• Quenching of the accretion disk strong aperiodic variability at the magnetospheric boundary
• Outbursts Large and Small from EXO 2030+375
• Identification of black hole power spectral components across all canonical states
• A Frequency Glitch in an Accreting Pulsar
• Evolution of the 0.01 - 25 Hz power spectral components in Cygnus X-1
• A comment on the colour-colour diagrams of Low Mass X-ray Binaries
• Broadband Observations of the Be/X-ray Binary Pulsar RX J0440.9+4431: Discovery of a Cyclotron Absorption Line
• The Be/X-ray transient 4U 0115+63/V635 Cassiopeiae. III. Quasi-cyclic variability
• Cyclotron resonance energies at a low X-ray luminosity: A0535+262 observed with Suzaku
• Spectral Formation in X-Ray Pulsars: Bulk Comptonization in the Accretion Shock
• Spectral Study of the Galactic Ridge X-ray Emission with Suzaku
• INTEGRAL and Swift observations of EXO 2030+375 during a giant outburst
• Energy-Dependent Harmonic Ratios of the Cyclotron Features of X0331+53 in the 2004-2005 Outburst
• Study of the cyclotron feature in MXB 0656-072
• The pre-outburst flare of the A 0535+26 August/September 2005 outburst
• Accretion disc formation around the neutron star in Be/X-ray binaries
• Discovery of a 0.02 Hz QPO feature in the Transient X-ray Pulsar KS 1947+300
• Discovery of pulsations in the X-ray transient 4U 1901+03
• Rapid spectral and timing variability of Be/X-ray binaries during type II outbursts
• Timing and spectral studies of the transient X-ray pulsar GX 304-1 during an outburst
• Finding a 24-day orbital period for the X-ray binary 1A 1118-616
• Timing and broad band spectroscopy of 1A 1118-61 with Suzaku
• The Be/X-ray transient KS 1947+300
• On the neutron star-disc interaction in Be/X-ray binaries
• RXTE observations of the 1A 1118-61 in an outburst, and the discovery of a cyclotron line
• Suzaku observation of the transient X-ray pulsar GRO J1008-57
• Cyclotron Resonance Energies and Orbital Elements of Accretion Pulsar 4U 0115+63 During the Giant Outburst in 2008
• Discovery of new quasi-periodic oscillations in the X-ray transient source V~0332+53
• The broad band spectral properties of binary X-ray pulsars
• The Orbital Period of Swift J1626.6-5156
• Gamma-ray observations of the Be/pulsar binary 1A 0535+262 during a giant X-ray outburst
• Bright flares from the X-ray pulsar SWIFT J1626.6-5156
• Multi-wavelength study of the Be/X-ray binary MXB 0656-072
• Discovery of a QPO in the X-ray pulsar 1A 1118-615: correlated spectral and aperiodic variability
• Timing and X-ray Spectral Features of Swift J1626.6-5156
• Correlated X-ray spectral and timing variability of the Be/X-ray binary V0332+53/BQ Cam during a type II outburst
• New insights into the Be/X-ray binary system MXB 0656-072
• Multi-frequency observations of SWIFT J1626.6-5156

Cited by in corpus (79)

• Cyclotron lines in highly magnetized neutron stars
• NICER and Fermi GBM Observations of the First Galactic Ultraluminous X-ray Pulsar Swift J0243.6+6124
• On the dependence of the X-ray continuum variations with luminosity in accreting X-ray pulsars
• An INTEGRAL overview of High Mass X-ray Binaries: classes or transitions?
• The 2019 super-Eddington outburst of RX J0209.6-7427: Detection of pulsations and constraints on the magnetic field strength
• GRO J1008-57: an (almost) predictable transient X-ray binary
• Discovery and Modeling of a Flattening of the Positive Cyclotron Line/Luminosity Relation in GX 304-1 with RXTE
• Luminosity-dependent spectral and timing properties of the accreting pulsar GX 304-1 measured with INTEGRAL
• RX J0440.9+4431: a persistent Be/X-ray binary in outburst
• MHD instabilities in accretion mounds - II. 3D simulations
• Long-term optical variability of high-mass X-ray binaries. II. Spectroscopy
• Accreting, highly magnetized neutron stars at the Eddington limit: A study of the 2016 outburst of SMC X-3
• The Intermediate Luminosity Optical Transient SN 2010da: The Progenitor, Eruption and Aftermath of a Peculiar Supergiant High-mass X-ray Binary
• Accretion regimes in the X-ray pulsar 4U 1901+03
• Measurements of Cyclotron Features and Pulse Periods in the High-Mass X-Ray Binaries 4U 1538-522 and 4U 1907+09 with INTEGRAL
• Complex variations of X-ray polarization in the X-ray pulsar LS V +44 17/RX J0440.9+4431
• Long-term pulse period evolution of the ultra-luminous X-ray pulsar NGC 7793 P13
• Radiative Relativistic Magnetohydrodynamic Simulations of Neutron Star Column Accretion in Cartesian Geometry
• A polarimetrically oriented X-ray stare at the accreting pulsar EXO 2030+375
• Revisiting the spectral and timing properties of 4U 1909+07 with NuSTAR and Astrosat
• Continuum, cyclotron line, and absorption variability in the high-mass X-ray binary Vela X-1
• The Transient Accereting X-Ray Pulsar XTE J1946+274: Stability of the X-Ray Properties at Low Flux and Updated Orbital Solution
• A new candidate Wolf-Rayet X-ray binary in NGC 253
• Study of timing and spectral properties of the X-ray pulsar 1A 0535+262 during the giant outburst in 2020 November-December
• Spectral and timing studies of 2S 1417-624 during a giant outburst
• RX J0440.9+4431: another supercritical X-ray pulsar
• Timing and spectral analysis of 2S 1417$-$624 during its 2018 outburst
• Type I outbursts in low eccentricity Be/X-ray binaries
• X-ray outbursts of ESO 243-49 HLX-1: comparison with Galactic low-mass X-ray binary transients
• NuSTAR detection of hard X-ray phase lags from the accreting pulsar GS 0834-430
• Discovery of a 168.8 s X-ray pulsar transiting in front of its Be companion star in the Large Magellanic Cloud
• Simulating the shock dynamics of a neutron star accretion column
• Evidence for different accretion regimes in GRO J1008-57
• RX J0529.8-6556: a BeXRB pulsar with an evolving optical period and out of phase X-ray outbursts
• Activity from the Be/X-ray binary system V0332+53 during its intermediate-luminosity outburst in 2008
• Three-dimensional modelling of accretion columns: spatial asymmetry and self-consistent simulations
• A new sample of transient ultraluminous X-ray sources serendipitously discovered by Swift/XRT
• Evolution of timing and spectral characteristics of 4U 1901+03 during its 2019 outburst using the Swift and NuSTAR observatories
• Switches between accretion structures during flares in 4U 1901+03
• NuSTAR view of Be/X-ray binary pulsar 2S 1417-624 during 2018 giant outburst
• The Effect of Variability on X-Ray Binary Luminosity Functions: Multiple Epoch Observations of NGC 300 with Chandra
• Spectral & Timing analysis of Be/X-ray binary EXO 2030+375 during its giant 2021 outburst
• Optical and X-ray studies of Be/X-ray binary 1A 0535+262 during its 2020 giant outburst
• Cyclotron line evolution revealed with pulse-to-pulse analysis in the 2020 outburst of 1A 0535+262
• X-ray emission evolution of the Galactic ultra-luminous X-ray pulsar Swift J0243.6+6124 during the 2017-2018 outburst observed by the MAXI GSC
• The giant outburst of EXO 2030+375 I: Spectral and pulse profile evolution
• Discovery of X-ray pulsations in the Be/X-ray binary IGR J21343+4738
• A high-mass X-ray binary pulsar 4U 1907+09 with multiple absorption-line features in the spectrum
• Comprehensive broadband study of accreting neutron stars with Suzaku: Is there a bi-modality in the X-ray spectrum?
• Probing spectral and timing properties of the X-ray pulsar RX J0440.9+4431 in the giant outburst of 2022-2023
• X-Ray Views of Galactic Accreting Pulsars in High-Mass X-Ray Binaries
• Quiescent X-ray variability in the neutron star Be/X-ray transient GRO J1750-27
• Inertial oscillation modes of an inclined dipolar magnetosphere as a source of band-limited noise in X-ray pulsars
• The unaltered pulsar: GRO J1750-27, a super-critical X-ray neutron star that does not blink an eye
• Probing the Mysteries of the X-Ray Binary 4U 1210-64 with ASM, PCA, MAXI, BAT and Suzaku
• NuSTAR observation of GRO J1744-28 at low mass accretion rate
• In-depth study of long-term variability in the X-ray emission of the Be/X-ray binary system AX J0049.4-7323
• Timing and Spectral Study of IGR J19294+1816 with RXTE: Discovery of Cyclotron Feature
• Timing and spectral studies of Cen X-3 in multiple luminosity states using $\text{AstroSat}$
• An X-ray view of the 2021 outburst of SXP 15.6: constraints on the binary orbit and magnetic field of the Neutron Star
• Timing and Spectral Studies of the X-ray Pulsar 2S 1417$-$624 During the Outburst in 2021
• X-ray spectral-timing variability of 1A 0535+262 during the 2020 giant outburst
• Timing and spectral properties of Be/Xray pulsar 4U 1901+03 during 2019 outburst
• Observations of V0332+53 during the 2015 Outburst using Fermi/GBM, MAXI, Swift, and INTEGRAL
• The spin-down accretion regime of Galactic ultra-luminous X-ray pulsar Swift J0243.6+6124
• Spectral and timing analysis of the bursting pulsar GRO J1744-28 with RXTE observations
• The Be/X-ray binary system V 0332+53: A Short Review
• Spectral and timing analysis of BeXRB eRASSU J050810.4-660653 recently discovered in the Large Magellanic Cloud (LMC)
• Monte-Carlo simulations on possible collimation effects of outflows to fan-beamed emission of ultraluminous accreting X-ray pulsars
• RXTE and SWIFT Observations of SWIFT J1729.9-3437
• Study of recently discovered Be/X-ray pulsar MAXI J0655-013 using NuSTAR
• Detection of a cyclotron line in the Be X-ray pulsar IGR J06074$+$2205
• Spectral states in Be/X-ray pulsars
• Spectral and Timing properties of the recently discovered Be/X-ray pulsar eRASSUJ 052914.9-662446
• Timing and spectral studies of the Be/X-ray binary EXO 2030+375 using Insight-HXMT observations
• Timing and spectral variability in 2S 1417-624 observed with Insight-HXMT
• Luminosity dependence of the cyclotron line energy in 1A 0535+262 observed by Insight-HXMT during 2020 giant outburst
• A study of the accretion mechanisms of the High Mass X-ray Binary IGR J00370+6122
• Super-critical accretion of BeXRB SXP 15.3