Characterizing the Evolving X-Ray Spectral Features During a Superburst from 4U 1636-536

Abstract

Recent studies have shown that runaway thermonuclear burning of material accreted onto neutron stars, i.e. Type I X-ray bursts, may affect the accretion disk. We investigate this by performing a detailed time-resolved spectral analysis of the superburst from 4U 1636-536 observed in 2001 with the Rossi X-ray Timing Explorer. Superbursts are attributed to the thermonuclear burning of carbon, and are approximately 1000 times more energetic than the regular short Type I bursts. This allows us to study detailed spectra for over 11 ks, compared to at most 100 s for regular bursts. A feature is present in the superburst spectra around 6.4 keV that is well fit with an emission line and an absorption edge, suggestive of reflection of the superburst off the accretion disk. The line and edge parameters evolve over time: the edge energy decreases from 9.4 keV at the peak to 8.1 keV in the tail, and both features become weaker in the tail. This is only the second superburst for which this has been detected, and shows that this behavior is present even without strong radius expansion. Furthermore, we find the persistent flux to almost double during the superburst, and return to the pre-superburst level in the tail. The combination of reflection features and increased persistent emission indicates that the superburst had a strong impact on the inner accretion disk, and it emphasizes that X-ray bursts provide a unique probe of accretion physics.

11 pages, 4 figures, 2 tables. Submitted for publication in ApJ

References in corpus (8)

• Thermonuclear (type-I) X-ray bursts observed by the Rossi X-ray Timing Explorer
• Relativistic X-ray Lines from the Inner Accretion Disks Around Black Holes
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• Superburst Models for Neutron Stars with Hydrogen and Helium-Rich Atmospheres
• Millihertz Oscillation Frequency Drift Predicts the Occurrence of Type I X-ray Bursts
• Carbon Detonation and Shock-Triggered Helium Burning in Neutron Star Superbursts

Cited by in corpus (8)

• Evidence for enhanced persistent emission during sub-Eddington thermonuclear bursts
• Accretion disks and coronae in the X-ray flashlight
• The influence of accretion geometry on the spectral evolution during thermonuclear (type-I) X-ray bursts
• Discovery of a Neutron Star Oscillation Mode During a Superburst
• X-ray Reflection and An Exceptionally Long Thermonuclear Helium Burst from IGR J17062-6143
• X-Raying an Accretion Disk in Realtime: the Evolution of Ionized Reflection during a Superburst from 4U 1636-536
• NICER Discovers Spectral Lines During Photospheric Radius Expansion Bursts from 4U 1820-30: Evidence for Burst-driven Winds
• Diagnosing the burst influence upon accretion in the clocked burster GS 1826--238