Gabriel Török*

3:2 controversy …hope for underlying QPO physics ?

*Institute of Physics, Faculty of Philosophy and Science, Silesian University in Opava, Bezručovo nám. 13, CZ-74601 Opava, Czech Republic

The presentation draws mainly from a collaboration with

M.A. Abramowicz, D. Barret, P.Bakala, M. Bursa, J. Horák, W. Kluzniak, M. Urbanec, and Z. Stuchlík

1.1. X-ray timing observations of low mass X-ray binaries

Figs on this page: nasa.gov

LMXBs short-term X-ray variability

• Low frequency QPOs (up to 100Hz)

• hecto-hertz QPOs (100-200Hz)

• kHz QPOs (~200-1500Hz)

frequency

pow

er

Sco X-1

1.2. kHz Quasiperiodic oscillations: BH and NS

Upp

er Q

PO fr

eque

ncy

Upp

er Q

PO fr

eque

ncy

LoweLower QPO frequencyr QPO frequency

Neutron starsNeutron stars

Black holesBlack holes(microquasars)(microquasars)

1.3.Ratio clustering

Upp

er Q

PO fr

eque

ncy

Upp

er Q

PO fr

eque

ncy

LoweLower QPO frequencyr QPO frequency

Neutron starsNeutron stars

Abramowicz et al. (2003), A&AAbramowicz et al. (2003), A&A

1.3.Ratio clustering Histograms of frequency ratio for observations displaying two significant kHz QPOs (Abramowicz et al 2005) in six atoll sources. Histograms peaks close to

3:23:2 3:23:2 3:23:25:45:4 3:23:25:45:4

4:34:3 4:34:3

2. 3:2 controversy ??

Belloni et al. (2004,2005A&A) studied frequency distributions in several sources. They confirmed the clustering around 3:2 and other ratios, but put some doubts on its interpretation.

Consequently, Belloni et al. (2007,MNRAS) examined lower QPO frequency distibution in the atoll source 4U 1636-53 and assuming a linear correlation between lower and upper kHz QPO frequency discussed the inferred ratio dstribution. They concluded that there is no preferred ratio in the source.

This result contradicts previous finding of ratio clustering in 1636-53.

The observational data we use here correspond to all the RXTE observations of the atoll source 4U 1636+53 proceeded by the shift-add technique through continuous segments of observation (the analysis of Barret et al. 2005).

The part of data displaying significant twin peak QPOs is restricted to about 20 hours of observation.

2.2 Exploring 4U 1636-53 kHz QPO data

The part of data displaying significant twin peak QPOs is restricted to about 20 hours of observation.

The detections of the single significant QPOs extend to about 10 times larger part of observations.

It is possible to determine whether the single peaks belong to group of upper or lower QPOs safely using the Quality factor diagram (Barret 2005).

We have therefore- significant lower QPO detections (lower QPOs)- significant upper QPO detections (upper QPOs)- twin QPOs (overlap between lower and upper QPO observations)

2.2 Exploring 4U 1636-53 kHz QPO data

lower QPOs upper QPOs

2.3 Distributions

twin QPOs

- significant lower QPO detections (lower QPOs)- significant upper QPO detections (upper QPOs)- twin QPOs (overlap between lower and upper QPO observations)

(T(Torokorok et al. (2008), A et al. (2008), AccAA submitted submitted))

2.3 Ratio distribution

(T(Torokorok et al. (2008), A et al. (2008), AccAA submitted submitted))

2.4 Resolving the controversy

correlation between lower and upper QPOfrequency (used by Belloni at al. 2007)

Distribution of ratio inferred from lower QPO frequency distibution differs from those inferred from upper and both differe from really observed distribution of ratio. There are the preferred frequency ratios.

3. Implications for orbital kHz QPO models …hope for underlaying physics ?

Figs on this page: nasa.gov

3.Implications for orbital models

lower QPOslower QPOstwin QPOstwin QPOs upper QPOsupper QPOs

=>

For models which identifies given QPO For models which identifies given QPO frequency to an orbital radius, one can look frequency to an orbital radius, one can look from where the oscillations come. from where the oscillations come. Here we Here we focus on the relativistic precession model of focus on the relativistic precession model of Stella and vietri.Stella and vietri.

TTorokorok et al. (2008), et al. (2008),AAccA, acceptedA, accepted

RatioRatio

radiusradius

3.Bonus

Here we focus on the relativistic precession model of Stella and vietri.Here we focus on the relativistic precession model of Stella and vietri.

lower QPOslower QPOstwin QPOstwin QPOs upper QPOsupper QPOs

Difference betweenDifference betweenlower and upper QPOlower and upper QPOamplitude [%]amplitude [%]TTorokorok (2008), A&A, submitted (2008), A&A, submitted

4. References

Figs on this page: nasa.gov

5. References

• Abramowicz et al., A&A L, 2003 • Barret et al., 2005, MNRAS• Belloni et al., 2005, A&A• Mendez, 2006, MNRAS• Belloni et al., 2007, MNRAS• Torok, 2007, A&A L, submitted

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