X-Raying an Accretion Disk in Realtime: the Evolution of Ionized Reflection during a Superburst from 4U 1636-536

Abstract

When a thermonuclear X-ray burst ignites on an accreting neutron star, the accretion disk undergoes sudden strong X-ray illumination, which can drive a range of processes in the disk. Observations of superbursts, with durations of several hours, provide the best opportunity to study these processes and to probe accretion physics. Using detailed models of ionized reflection, we perform time resolved spectroscopy of the superburst observed from 4U 1636-536 in 2001 with RXTE. The spectra are consistent with a blackbody reflecting off a photoionized accretion disk, with the ionization state dropping with time. The evolution of the reflection fraction indicates that the initial reflection occurs from a part of the disk at larger radius, subsequently transitioning to reflection from an inner region of the disk. Even though this superburst did not reach the Eddington limit, we find that a strong local absorber develops during the superburst. Including this event, only two superbursts have been observed by an instrument with sufficient collecting area to allow for this analysis. It highlights the exciting opportunity for future X-ray observatories to investigate the processes in accretion disks when illuminated by superbursts.

6 pages, 2 figures, accepted for publication by ApJ Letters

References in corpus (5)

• Thermonuclear (type-I) X-ray bursts observed by the Rossi X-ray Timing Explorer
• The effect of accretion on the measurement of neutron star mass and radius in the low-mass X-ray binary 4U 1608-52
• Detection of the Irradiated Donor in the LMXBs 4U 1636-536 (=V801 Ara) and 4U 1735-444 (=V926 Sco)
• Characterizing the Evolving X-Ray Spectral Features During a Superburst from 4U 1636-536
• The Large Observatory For x-ray Timing

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• NICER Discovers Spectral Lines During Photospheric Radius Expansion Bursts from 4U 1820-30: Evidence for Burst-driven Winds
• Neutron star cooling and the rp process in thermonuclear X-ray bursts
• Burst-induced coronal cooling in GS 1826-24 The clock wagging its tail
• NICER observations of the evidence of Poynting-Robertson drag and disk reflection during type I X-ray bursts from 4U 1636$-$536
• Variable spreading layer in 4U 1608-52 during thermonuclear X-ray bursts in the soft state
• Insight-HXMT observation on 4U~1608--52: evidence of interplay between thermonuclear burst and accretion environments
• Evolution of accretion disc reflection spectra due to a Type I X-ray burst
• Broadband time-resolved spectroscopy of thermonuclear X-ray bursts from 4U 1636-536 using AstroSat
• Radiation Driven Warping of Accretion Discs Due to X-ray Bursts
• On the impact of an intermediate duration X-ray burst on the accretion environment in IGR J17062-6143