Aperiodic variability study of the accreting millisecond pulsar IGR - - PowerPoint PPT Presentation

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Aperiodic variability study of the accreting millisecond pulsar IGR J17511-3057 Maithili Kalamkar Diego Altamirano Michiel van der Klis University of Amsterdam Black hole variability 2010, University of Southampton 1 a. Introduction to the

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Aperiodic variability study of the accreting millisecond pulsar IGR J17511-3057

Maithili Kalamkar

Diego Altamirano Michiel van der Klis University of Amsterdam

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a. Introduction to the source IGR J17511-3057

Discovered on September 12th 2009 by INTEGRAL AMP with spin frequency 244.8 Hz Exhibited type-I x-ray bursts Orbital period 207.4 minutes Companion star mass estimate 0.13 solar mass Distance estimate 6.87 kpc Fig. 1. Low Mass X-ray Binary

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b. Colo(u)r analysis
Fig. 2. Intensity, hard and soft colours. Each point

corresponds to one observation Hard color = 9.7-16/6.0- 9.7 keV, Soft colour = 3.5-6/2-3.5 keV

The hard and soft colors correlate with the intensity during the entire

utburst

Similar to AMPs - XTE J1807-294 and XTE J1751-305 In other sources, hard color does not correlate with intensity

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b. Colo(u)r analysis

Source appears to be an atoll in the Extreme Island State

Fig. 3. Color-color Diagram of IGR J17511-3057 and a typical atoll source.

Hard color = 9.7-16/6.0-9.7 keV, Soft colour = 3.5-6/2-3.5 keV

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c. Aperiodic variability

RXTE - PCA data Fourier analysis of Event mode in 2 16 keV energy range –

Fig. 4. Power spectrum of group3 with fit and power spectrum in a typical extreme island state

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c. Aperiodic variability

Not all power spectra resemble the power spectrum expected in the Extreme Island State observed in other sources

Fig. 5. Power spectrum of group1 with fit and power spectrum in a typical Lower Left

Banana branch

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e. Identification of features
Fig. 6. Frequency-frequency correlations as seen in LMXBs

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e. Implications

If the high frequency features are kHz QPOs, then

kHz QPOs in Extreme Island State (one exception, 4U 1728-34; Migliari et al.2003)
Measured differences Δν are 112 ±13, 144.9±18.4 and 104.2±15 respectively ;

inconsistent with the spin frequency νs of 244.8 Hz ( νs < 400 Hz) but close to νs/2 instead as is the case seen in fast rotators ( νs > 400 Hz) ; Miller et al. 1998

Fig.7 Ratio of measurements of Δν/νs vs. νs

Mendez , Belloni et al. 2007, Altamirano et. al 2010

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