A NICER look at the Aql X-1 hard state
- Bult, Peter
- Arzoumanian, Zaven
- Cackett, Edward M.
- Chakrabarty, Deepto
- Gendreau, Keith C.
- Guillot, Sebastien
- Homan, Jeroen
- Jaisawal, Gaurava K.
- Keek, Laurens
- Kenyon, Steve
- Lamb, Frederick K.
- Ludlam, Renee
- Mahmoodifar, Simin
- Markwardt, Craig
- Miller, Jon M.
- Prigozhin, Gregory
- Soong, Yang
- Strohmayer, Tod E.
- Uttley, Phil
DOIAbstract
International audienceWe report on a spectral-timing analysis of the neutron star low-mass X-ray binary (LMXB) Aql X-1 with the Neutron Star Interior Composition Explorer (NICER) on the International Space Station (ISS). Aql X-1 was observed with NICER during a dim outburst in 2017 July, collecting approximately 50 ks of good exposure. The spectral and timing properties of the source correspond to that of a (hard) extreme island state in the atoll classification. We find that the fractional amplitude of the low-frequency (<0.3 Hz) band-limited noise shows a dramatic turnover as a function of energy: it peaks at 0.5 keV with nearly 25% rms, drops to 12% rms at 2 keV, and rises to 15% rms at 10 keV. Through the analysis of covariance spectra,...
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