An enigmatic hump around 30 keV in Suzaku spectra of Aquila X-1 in the Hard State. (arXiv:1902.05225v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Kubota_M/0/1/0/all/0/1">Megu Kubota</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Tamagawa_T/0/1/0/all/0/1">Toru Tamagawa</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Makishima_K/0/1/0/all/0/1">Kazuo Makishima</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Nakano_T/0/1/0/all/0/1">Toshio Nakano</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Iwakiri_W/0/1/0/all/0/1">Wataru Iwakiri</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Sugizaki_M/0/1/0/all/0/1">Mutsumi Sugizaki</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ko_O/0/1/0/all/0/1">Ono Ko</a>
The typical accreting neutron star, Aquila X-1, was observed with Suzaku
seven times in the decay phase of an outburst in 2007 September-October. Among
them, the second to the fourth observations were performed 10 to 22 days after
the outburst peak, when the source was in the hard state with a luminosity of
2×10^36 erg/sec. A unified spectral model for this type of objects
approximately reproduced the 0.8–100~keV spectra obtained in these 3
observations. However, the spectra all exhibited an enigmatic hump-like excess
around 30 keV, above the hard X-ray continuum which is interpreted as arising
via Comptonization. The excess feature was confirmed to be significant against
statistical and systematic uncertainties. It was successfully represented by a
Gaussian centered at ~32 keV, with a width (sigma) of ~6 keV and an equivalent
width of ~8.6 keV. Alternatively, the feature can also be explained by a
recombination edge model, that produces a quasi-continuum above an edge energy
of ~27 keV with an electron temperature of ~11 keV and an equivalent width of
~6.3 keV. These results are discussed in the context of atomic features of
heavy elements synthesized via rapid-proton capture process during
thermonuclear flashes.
The typical accreting neutron star, Aquila X-1, was observed with Suzaku
seven times in the decay phase of an outburst in 2007 September-October. Among
them, the second to the fourth observations were performed 10 to 22 days after
the outburst peak, when the source was in the hard state with a luminosity of
2×10^36 erg/sec. A unified spectral model for this type of objects
approximately reproduced the 0.8–100~keV spectra obtained in these 3
observations. However, the spectra all exhibited an enigmatic hump-like excess
around 30 keV, above the hard X-ray continuum which is interpreted as arising
via Comptonization. The excess feature was confirmed to be significant against
statistical and systematic uncertainties. It was successfully represented by a
Gaussian centered at ~32 keV, with a width (sigma) of ~6 keV and an equivalent
width of ~8.6 keV. Alternatively, the feature can also be explained by a
recombination edge model, that produces a quasi-continuum above an edge energy
of ~27 keV with an electron temperature of ~11 keV and an equivalent width of
~6.3 keV. These results are discussed in the context of atomic features of
heavy elements synthesized via rapid-proton capture process during
thermonuclear flashes.
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