Large X-ray Flares from LMC X-4: Discovery of Milli-hertz Quasi-periodic Oscillations and QPO-modulated Pulsations

Abstract

We report the discovery of milli-hertz (mHz) quasi-periodic oscillations (QPOs) and QPO-modulated pulsations during large X-ray flares from the high-mass X-ray binary pulsar LMC X-4 using data from the Rossi X-Ray Timing Explorer (RXTE). The lightcurves of flares show that, in addition to ~74 mHz coherent pulsations, there exist two more time-varying temporal structures at frequencies of ~0.65-1.35 and ~2-20 mHz. These relatively long-term structures appear in the power density spectra as mHz QPOs and as well-developed sidebands around the coherent pulse frequency as well, indicating that the amplitudes of the coherent pulsation is modulated by those of the mHz QPOs. One interesting feature is that, while the first flare shows symmetric sidebands around the coherent pulse frequency, the second flare shows significant excess emission in the lower-frequency sidebands due to the ~2-20 mHz QPOs. We discuss the origin of the QPOs using a combination of the beat-frequency model and a modified version of the Keplerian-frequency model. According to our discussion, it seems to be possible to attribute the origin of the ~0.65-1.35 and ~2-20 mHz QPOs to the beating between the rotational frequency of the neutron star and the Keplerian frequency of large accreting clumps near the corotation radius and to the orbital motion of clumps at Keplerian radii of 2-10 times 10^9 cm, respectively.

12 pages, including 4 figures; accepted by ApJ Letters

Cited by in corpus (26)

• Long-term Properties of Accretion Disks in X-ray Binaries: II. Stability of Radiation-Driven Warping
• Chandra Grating Spectroscopy of the X-ray Binary 4U 1700-37 in a Flaring State
• Can disk-magnetosphere interaction models and beat frequency models for quasi-periodic oscillation in accreting X-ray pulsars be reconciled?
• Large Highly-Ionized Nebulae Around Ultra-luminous X-ray Sources
• Discovery of a 0.02 Hz QPO feature in the Transient X-ray Pulsar KS 1947+300
• Magnetically Driven Precession of Warped Disks and Milli-Hertz Variabilities in Accreting X-Ray Pulsars
• Discovery of Soft Spectral Component and Transient 22.7s Quasi Periodic Oscillations of SAX J2103.5+4545
• Stellar wind accretion and accretion disk formation: applications to neutron star high mass X-ray binaries
• Quasi periodic oscillations in XTE J0111.2--7317, highest frequency among the HMXB pulsars
• RXTE-PCA observations of 1A 1118--61: timing and spectral studies during an outburst
• The Evolution Of LMC X-4 Flares: Evidence For Super-Eddington Radiation Oozing Through Inhomogeneous Polar Cap Accretion Flows ?
• Observations of the X-ray pulsar LMC X-4 with NuSTAR: limit on the magnetic field and tomography of the system in the fluorescent iron line
• Discovery of Coupling between Periodic and Aperiodic Variability and X-ray Quasi-periodic Oscillations from Her X-1
• Broadband mHz QPOs and spectral study of LMC X$-$4 with AstroSat
• Determination of parameters of long-term variability of the X-ray pulsar LMC X-4
• Post-flare Formation of the Accretion Stream and a Dip in Pulse Profiles of LMC X-4
• Flares, Broadening of the Pulse frequency peak, and Quasi Periodic Oscillations in the Transient X-ray Pulsar 4U 1901+03
• Discovery of pulsation dropout and turn-on during the high state of the accreting X-ray pulsar LMC X-4
• Quasi periodic whispers from a transient ULX in M\,101: signatures of a fast-spinning neutron star?
• Peculiarities of super-Eddington flares from the X-ray pulsar LMC X-4 with NuSTAR
• Discovery of Quasi Periodic Oscillations in the persistent X-ray emission of Accreting Binary X-ray Pulsar LMC X-4
• SALT observation of X-ray pulse reprocessing in 4U 1626-67
• Variability study of the High Mass X-ray Binary IGR J18027--2016 with {\it Swift}--XRT
• X-ray stellar population of the LMC
• Timing and Spectral Analysis of 4U 1626-67 Using AstroSat/LAXPC
• Probing accretion dynamics and spin evolution in the X-ray pulsar RX J0520.5-6932 during its 2024 Outburst