The drop of the coherence of the lower kHz QPOs is also observed in XTE J1701-462 - Astrophysics > High Energy Astrophysical PhenomenaReportar como inadecuado




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Abstract: We investigate the quality factor and RMS amplitude of the lower kHz QPOsfrom XTE J1701-462, a unique X-ray source which was observed in both theso-called Z and atoll states. Correcting for the frequency drift of the QPO, weshow that, as in all sources for which such a correction can be applied, thequality factor and RMS amplitude drops sharply above above a criticalfrequency. For XTE J1701-462 this frequency is estimated to be ~800 Hz, wherethe quality factor reaches a maximum of ~200 e.g. a value consistent with theone observed from more classical systems, such as 4U~1636-536. Such a drop hasbeen interpreted as the signature of the innermost stable circular orbit, andthat interpretation is consistent with the observations we report here. The kHzQPOs in the Z state are much less coherent and lower amplitude than they are inthe atoll state. We argue that the change of the QPO properties between the twosource states is related to the change of the scale height of the accretiondisk; a prediction of the toy model proposed by barret et al. 2007. As aby-product of our analysis, we also increased the significance of the upper kHzQPO detected in the atoll phase up to 4.8 sigma single trial significance,and show that the frequency separation 266.5+-13.1 Hz is comparable with theone measured from simultaneous twin QPOs the Z phase.



Autor: Didier Barret CESR, Toulouse, Matteo Bachetti CESR, Toulouse, M. Coleman Miller University of Maryland, College Park

Fuente: https://arxiv.org/







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