Evolution of accretion disc reflection spectra due to a Type I X-ray burst. (arXiv:2110.11931v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Speicher_J/0/1/0/all/0/1">J. Speicher</a> (1), <a href="http://arxiv.org/find/astro-ph/1/au:+Ballantyne_D/0/1/0/all/0/1">D. R. Ballantyne</a> (1), <a href="http://arxiv.org/find/astro-ph/1/au:+Fragile_P/0/1/0/all/0/1">P. C. Fragile</a> (2) ((1) Center for Relativistic Astrophysics, School of Physics, Georgia Institute of Technology, (2) Department of Physics & Astronomy, College of Charleston)
Irradiation of the accretion disc causes reflection signatures in the
observed X-ray spectrum, encoding important information about the disc
structure and density. A Type I X-ray burst will strongly irradiate the
accretion disc and alter its properties. Previous numerical simulations
predicted the evolution of the accretion disc due to an X-ray burst. Here, we
process time-averaged simulation data of six time intervals to track changes in
the reflection spectrum from the burst onset to just past its peak. We divide
the reflecting region of the disc within $rlesssim50$ km into 6-7 radial zones
for every time interval and compute the reflection spectra for each zone. We
integrate these reflection spectra to obtain a total reflection spectrum per
time interval. The burst ionizes and heats the disc, which gradually weakens
all emission lines. Compton scattering and bremsstrahlung rates increase in the
disc during the burst rise, and the soft excess at $<$3 keV rises from
$approx4$% to $approx38$% of the total emission at the burst peak. A soft
excess is expected to be ubiquitous in the reflection spectra of X-ray bursts.
Structural disc changes such as inflation because of heating or drainage of the
inner disc due to Poynting-Robertson drag affect the strength of the soft
excess. Further studies on the dependence of the reflection spectrum
characteristics to changes in the accretion disc during an X-ray burst may lead
to probes of the disc geometry.
Irradiation of the accretion disc causes reflection signatures in the
observed X-ray spectrum, encoding important information about the disc
structure and density. A Type I X-ray burst will strongly irradiate the
accretion disc and alter its properties. Previous numerical simulations
predicted the evolution of the accretion disc due to an X-ray burst. Here, we
process time-averaged simulation data of six time intervals to track changes in
the reflection spectrum from the burst onset to just past its peak. We divide
the reflecting region of the disc within $rlesssim50$ km into 6-7 radial zones
for every time interval and compute the reflection spectra for each zone. We
integrate these reflection spectra to obtain a total reflection spectrum per
time interval. The burst ionizes and heats the disc, which gradually weakens
all emission lines. Compton scattering and bremsstrahlung rates increase in the
disc during the burst rise, and the soft excess at $<$3 keV rises from
$approx4$% to $approx38$% of the total emission at the burst peak. A soft
excess is expected to be ubiquitous in the reflection spectra of X-ray bursts.
Structural disc changes such as inflation because of heating or drainage of the
inner disc due to Poynting-Robertson drag affect the strength of the soft
excess. Further studies on the dependence of the reflection spectrum
characteristics to changes in the accretion disc during an X-ray burst may lead
to probes of the disc geometry.
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