TY - JOUR
T1 - Kilohertz quasi-periodic oscillations in neutron-star X-ray binaries
T2 - Flattening of the lag spectrum with increasing luminosity
AU - Peirano, Valentina
AU - Méndez, Mariano
N1 - Funding Information:
The authors wish to thank Federico Garc?a and Konstantinos Karpouzas for useful discussions that helped with the ideas presented in this manuscript. They also thank the referee for insightful comments that helped improve the clarity of the paper. This research has made use of data obtained from the High Energy Astrophysics Science ArchiveResearch Center, provided by NASA'sGoddard Space Flight Center.
Publisher Copyright:
© The Author(s) 2021.
PY - 2021/9/1
Y1 - 2021/9/1
N2 - We study the energy-dependent time lags and rms fractional amplitude of the kilohertz quasi-periodic oscillations (kHz QPOs) of a group of neutron-star low-mass X-ray binaries. We find that for the lower kHz QPO both the slope of the best-fitting linear model to the time-lag spectrum and the total rms amplitude integrated over the 2-25 keV energy band decrease exponentially with the luminosity of the source. For the upper kHz QPO, the slope of the time-lag spectrum is consistent with zero, while the total rms amplitude decreases exponentially with the luminosity of the source. We show that both the slope of the time-lag spectrum and the total rms amplitude of the lower kHz QPO are linearly correlated with a slope of ∼1. Finally, we discuss the mechanism that could be responsible for the radiative properties of the kHz QPOs, with the variability originating in a Comptonizing cloud or corona that is coupled to the innermost regions of the accretion disc, close to the neutron star.
AB - We study the energy-dependent time lags and rms fractional amplitude of the kilohertz quasi-periodic oscillations (kHz QPOs) of a group of neutron-star low-mass X-ray binaries. We find that for the lower kHz QPO both the slope of the best-fitting linear model to the time-lag spectrum and the total rms amplitude integrated over the 2-25 keV energy band decrease exponentially with the luminosity of the source. For the upper kHz QPO, the slope of the time-lag spectrum is consistent with zero, while the total rms amplitude decreases exponentially with the luminosity of the source. We show that both the slope of the time-lag spectrum and the total rms amplitude of the lower kHz QPO are linearly correlated with a slope of ∼1. Finally, we discuss the mechanism that could be responsible for the radiative properties of the kHz QPOs, with the variability originating in a Comptonizing cloud or corona that is coupled to the innermost regions of the accretion disc, close to the neutron star.
KW - Astrophysics - High Energy Astrophysical Phenomena
UR - http://www.scopus.com/inward/record.url?scp=85112332506&partnerID=8YFLogxK
U2 - 10.1093/mnras/stab1905
DO - 10.1093/mnras/stab1905
M3 - Article
SN - 0035-8711
VL - 506
SP - 2746
EP - 2752
JO - Monthly Notices of the Royal Astronomical Society
JF - Monthly Notices of the Royal Astronomical Society
IS - 2
ER -