Long Thermonuclear Burst–driven Thermal–Viscous Instability of Accretion Disk: Triggering an Outburst-like X-Ray Flare

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Chinese explanation / 中文解读

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Original abstract

Abstract We report on NICER and MAXI observations of a long-duration thermonuclear X-ray burst and a subsequent outburst-like X-ray flare from the neutron star low-mass X-ray binary MAXI J0911–655. Prior to the burst, the source was in a persistent low/hard state with a power-law-dominated spectrum (Γ ∼ 1.7) and a mass accretion rate of ∼1% of the Eddington limit. The long burst, detected by MAXI on 2020 May 22 (MJD 58991.7101), was rapidly followed up by NICER. From time-resolved spectroscopy of the cooling tail, we estimate an exponential decay time of ≈43 minutes, the ignition column depth of ≈0.1 × 10 12 g cm −2 , the burst fluence of ≈1.1 × 10 −4 erg cm −2 , and the total energy release of ≈1.2 × 10 42 erg. Approximately 1 day after the burst onset, the 0.5–10 keV light curve unexpectedly rebrightened, initiating an outburst-like flare. During the peak of this flare, the persistent power-law flux increased from its preburst level of ∼0.27 × 10 −9 –1.4 × 10 −9 erg cm −2 s −1 . This flux enhancement was accompanied by significant spectral softening, with the photon index increasing to Γ ∼ 2.2. Subsequently, the flux decayed and the source returned to its baseline low/hard state. The observed timescales and energetics suggest that intense irradiation from the long burst amplified the ongoing thermal–viscous accretion process. This heating drove an inside-out heating front that temporarily enhanced the mass accretion rate, providing compelling observational evidence of a thermonuclear burst directly modulating the accretion dynamics of its surrounding disk.

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