X-ray spectral-timing variability of 1A 0535+262 during the 2020 giant outburst

Abstract

The Be/X-ray binary 1A 0535+262 underwent a giant X-ray outburst in November 2020, peaking at $\sim 1\times 10^{38}$ erg s${}^{-1}$ (1--100 keV, 1.8 kpc), the brightest outburst recorded for this source so far. Our goal is to search for patterns of correlated spectral and timing behavior that can be used to characterize the accretion states in hard X-ray transient pulsars. We have studied the evolution of the spectral continuum emission using hardness-intensity diagrams and the aperiodic variability of the source. The hardness-intensity diagram displays three distinct branches that can be identified with different accretion regimes. The characteristic frequency of the noise components correlates with the luminosity. Our observations cover the highest end of this correlation, at luminosities not previously sampled. We have found evidence for a flattening of the correlation at those high luminosities, which might indicate that the accretion disk reached the closest distance from the neutron star surface during the peak of the outburst. We also find evidence for hysteresis in the spectral and timing parameters: at the same luminosity level, the spectrum is harder and the characteristic noise frequency larger during the rise than during the decay of the outburst.

References in corpus (14)

• Estimating distances from parallaxes. V: Geometric and photogeometric distances to 1.47 billion stars in Gaia Early Data Release 3
• The critical accretion luminosity for magnetized neutron stars
• Black hole-like hysteresis and accretion states in neutron star low mass X-ray binaries
• Patterns of variability in Be/X-ray pulsars during giant outbursts
• Luminosity dependence of the cyclotron line and evidence for the accretion regime transition in V 0332+53
• Cyclotron emission, absorption, and the two faces of X-ray pulsar A 0535+262
• Spectrum formation in X-ray pulsars at very low mass accretion rate: Monte-Carlo approach
• Rapid spectral and timing variability of Be/X-ray binaries during type II outbursts
• Broadband aperiodic variability in X-ray pulsars: accretion rate fluctuations propagating under the influence of viscous diffusion
• Cyclotron line formation by reflection on the surface of a magnetic neutron star
• Study of timing and spectral properties of the X-ray pulsar 1A 0535+262 during the giant outburst in 2020 November-December
• Radius of the neutron star magnetosphere during disk accretion
• Time-lag between disk and corona radiation leads to hysteresis effect observed in black-hole X-ray binary MAXI J1348-630
• Insight-HXMT observations of Swift J0243.6+6124: the evolution of RMS pulse fractions at super-Eddington luminosity

Cited by in corpus (4)

• High energy Millihertz quasi-periodic oscillations in 1A 0535+262 with Insight-HXMT challenge current models
• Cyclotron line evolution revealed with pulse-to-pulse analysis in the 2020 outburst of 1A 0535+262
• Probing spectral and timing properties of the X-ray pulsar RX J0440.9+4431 in the giant outburst of 2022-2023
• Unveiling the origin of the optical/UV emission from the Galactic ULX Swift J0243.6+6124 during its 2017-2018 giant outburst