http://arxiv.org/abs/1411.0684
We report the discovery of a $\sim 1.5 \times 10^{-4}$ Hz ($\sim 2$ hr) X-ray quasi-periodic oscillation (QPO) in the active galaxy MS 2254.9-3712, using a $\sim 70$ ks XMM-Newton observation. The QPO is significantly detected in the $1.2 – 5.0$ keV band only, connecting its origin with the primary X-ray power-law continuum. We detect a highly coherent soft lag between the $0.3 – 0.7$ keV and $1.2 – 5.0$ keV energy bands at the QPO and harmonic frequencies, with a 3:2 frequency ratio. An iron K$\alpha$ reverberation lag is found at the harmonic frequency, indicating the reflecting material subtends some angle to the primary continuum, which is modulated by the QPO mechanism. The coherence at the QPO and harmonic frequencies is ~ unity, whereas the coherence in the broadband noise is decreasing with increasing frequency. Frequency resolved spectroscopy reveals the QPO and harmonic to have a hard energy dependence. These properties of the QPO variability, together with the current black hole mass estimate, $M_{\rm BH} \sim 4 \times 10^{6} M_{\rm sun}$, are consistent with the QPO originating from the same process as the high frequency QPO phenomenon observed in black hole X-ray binaries. The discovery of iron K$\alpha$ reverberation responding to the QPO opens up the possibility of understanding both these variability processes in better detail.
W. Alston, M. Parker, J. Markeviciute, et. al.
Wed, 5 Nov 14
27/61
Comments: 9 pages, 8 figures. Submitted to MNRAS. Comments welcome
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