Study of timing and spectral properties of the X-ray pulsar 1A 0535+262 during the giant outburst in 2020 November-December

Abstract

We made a detailed study of the timing and spectral properties of the X-ray pulsar 1A 0535+262 during the recent giant outburst in 2020 November and December. The flux of the pulsar reached a record value of $\sim$12.5 Crab as observed by Swift/BAT (15--50 keV) and the corresponding mass accretion rate was $\sim 6.67\times 10^{17}$ g s${}^{-1}$ near the peak of the outburst. There was a transition from the subcritical to the supercritical accretion regime which allows exploring different properties of the source in the supercritical regime. A q-like feature was detected in the hardness-intensity diagram during the outburst. We observed high variability and strong energy dependence of pulse profiles during the outburst. Cyclotron Resonant Scattering Feature (CRSF) was detected at $\sim 44$ keV from the NuSTAR energy spectrum in the subcritical regime and the corresponding magnetic field was $B\simeq 4.9\times 10^{12}$ G. The energy of the CRSF was shifted towards lower energy in the supercritical regime. The luminosity dependence of the CRSF was studied and during the supercritical regime, a negative correlation was observed between the line energy and luminosity. The critical luminosity was $\sim 6\times 10^{37}$ erg s${}^{-1}$ above which a state transition occurred. A reversal of correlation between the photon index and luminosity was observed near the critical luminosity. The NuSTAR spectra can be described by a composite model with two continuum components, a blackbody emission, cut-off power law, and a discrete component to account for the iron emission line at 6.4 keV. An additional cyclotron absorption feature was included in the model.

10 pages, MNRAS (in press)

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Cited by in corpus (10)

• Timing properties of the X-ray accreting pulsar 1A 0535+262 studied with Insight-HXMT
• Optical and X-ray studies of Be/X-ray binary 1A 0535+262 during its 2020 giant outburst
• Swift J1728.9-3613 is a black hole X-ray binary: spectral and timing study using NICER
• Probing spectral and timing properties of the X-ray pulsar RX J0440.9+4431 in the giant outburst of 2022-2023
• Phase dependent evolution within large luminosity range of 1A 0535+262 observed by Insight-HXMT during 2020 giant outburst
• Timing and Spectral Studies of the X-ray Pulsar 2S 1417$-$624 During the Outburst in 2021
• Multiwavelength observation of 1A 0535+262=HD 245770 from 2010 to 2021
• Deep search for gamma-ray emission from the accreting X-ray pulsar 1A 0535+262
• X-ray spectral-timing variability of 1A 0535+262 during the 2020 giant outburst
• Temporal and spectral study of the X-ray pulsar 2S 1553-542 during the 2021 outburst