Spectral-Timing to Probe Strong Gravity in X-ray Binaries

Dissertation talk in the Black Holes II session at the American Astronomical Society meeting #229, Thursday January 5th, 2017.

X-ray spectral-timing seeks to investigate how matter behaves in strong gravitational fields. Observations suggest that different types of quasi-periodic oscillations (QPOs) are associated with different emission-region geometries (e.g. disk-like or jet-like) in the innermost part of an X-ray binary, close to the neutron star or black hole. We developed a technique for phase-resolved spectroscopy of QPOs, and have applied it to low-frequency QPOs from black hole X-ray binaries. On the QPO time-scale, we find that the energy spectrum changes not only in normalization, but also in spectral shape. We identify these changes as a phase-dependence of the intrinsic power-law emission as well as the response of the accretion disk to variable illumination by the power-law. We also look for systematic trends between different classes of sources and different accretion states. These trends help us to further constrain the origin of low-frequency QPOs and QPO evolution with the changing emission geometry in the strong-gravity regime.

Transcript

1. 
         Spectral-timing to probe strong gravity in X-ray binaries Abigail Stevens, Phil Uttley University of Amsterdam AAS 229
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         Low-Mass X-ray Binaries (LMXBs)
         Roche-lobe overflow Accretion disk Compact object Low-mass companion star Jet Figure: ESO/L. Calçada How does matter behave in strong gravitational fields?
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         Inner Region of an LMXB
         Disk Corona ×
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         Inner Region of an LMXB
         Disk Corona × Lense-Thirring precession Stella & Vietri 1998; Fragile & Anninos 2005; Schnittman, Homan & Miller 2006; Ingram, Done & Fragile 2009; Ingram & van der Klis 2015; Fragile et al. 2016; Ingram et al. 2016a,b
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         Inner Region of an LMXB
         Disk Corona × Lense-Thirring precession Stella & Vietri 1998; Fragile & Anninos 2005; Schnittman, Homan & Miller 2006; Ingram, Done & Fragile 2009; Ingram & van der Klis 2015; Fragile et al. 2016; Ingram et al. 2016a,b
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         Inner Region of an LMXB
         Disk Corona × Lense-Thirring precession Stella & Vietri 1998; Fragile & Anninos 2005; Schnittman, Homan & Miller 2006; Ingram, Done & Fragile 2009; Ingram & van der Klis 2015; Fragile et al. 2016; Ingram et al. 2016a,b
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         Inner Region of an LMXB
         Disk Corona × Lense-Thirring precession Stella & Vietri 1998; Fragile & Anninos 2005; Schnittman, Homan & Miller 2006; Ingram, Done & Fragile 2009; Ingram & van der Klis 2015; Fragile et al. 2016; Ingram et al. 2016a,b
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         Inner Region of an LMXB
         Disk Corona × Lense-Thirring precession Stella & Vietri 1998; Fragile & Anninos 2005; Schnittman, Homan & Miller 2006; Ingram, Done & Fragile 2009; Ingram & van der Klis 2015; Fragile et al. 2016; Ingram et al. 2016a,b
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         Inner Region of an LMXB
         Disk 1700 1702 1704 1706 1708 1710 Time (s) Start Time 12339 7:28:14:566 Stop Time 12339 7:29:32:683 Bin time: 0.7812E−02 s X-ray variability Corona ×
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          Inner Region of an LMXB
          Disk blackbody re-processing Corona 10 5 20 0.1 1 keV2 (Photons cm−2 s−1 keV−1) Energy (keV) power-law
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          Inner Region of an LMXB
          Disk blackbody re-processing Corona 10 5 20 0.1 1 keV2 (Photons cm−2 s−1 keV−1) Energy (keV) power-law 1700 1702 1704 1706 1708 1710 Time (s) Start Time 12339 7:28:14:566 Stop Time 12339 7:29:32:683 Bin time: 0.7812E−02 s X-ray variability
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          Quasi-Periodic Oscillations (QPOs)
          Power spectra show amount of variability at different frequencies in a light curve GX 339-4
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          Type B vs Type C QPOs
          Schnittman, Homan & Miller 2006; Motta et al 2015 (images); Heil et al 2015b 1 10 QPO centroid Frequency (Hz) 2 4 6 8 10 12 14 Fractional rms (%) 2 4 6 Fracti 2 4 6 8 10 12 14 Fractional rms (%) QPO rms (HI) QPO rms (LI) QPO rms (HI) Average QPO rms (HI) QPO rms (LI) Average QPO rms (LI) 0.1 1.0 10.0 QPO centroid Frequency (Hz) 5 10 15 20 25 Fractional rms (%) 5 10 Fracti 5 10 15 20 25 Fractional rms (%) QPO rms (HI) QPO rms (LI) QPO rms (HI) Average QPO rms (HI) QPO rms (LI) Average QPO rms (LI) 25 Type B’s: stronger face-on Type C’s: stronger edge-on (binary system inclination)
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          Phase-Resolved Spectroscopy •  New technique allows us to effectively do phase-resolved spectroscopy of QPOs •  Details in paper -- arXiv: 1605.01753 •  Deviations from mean energy spectrum •  Spectral shape is varying with QPO phase!
          10 5 20 0 0.5 keV2 (Photons cm−2 s−1 keV−1) Energy (keV) 0° 90° 180° 270° Type B
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          Type B QPO Spectral Variations •  Blackbody variation leads the power-law variation by ~0.3 (110°) •  Power-law: large variation •  Blackbody: small variation
         
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          Type B QPO Interpretation
          Large scale height, weakly modulated illumination ×
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          Type B QPO Interpretation
          × Large scale height, weakly modulated illumination
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          Type B QPO Interpretation
          × Large scale height, weakly modulated illumination
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          Type B QPO Interpretation
          × Large scale height, weakly modulated illumination
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          •  Different parameter phase relationship •  Power-law: smaller variation (compared to Type B) •  Blackbody: larger variation Type C QPO Spectral Variations
         
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          Type C QPO Interpretation
          Image: ESA/NASA/A. Ingram Small scale height, strongly modulated illumination ×
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          Type C QPO Interpretation
          Image: ESA/NASA/A. Ingram Small scale height, strongly modulated illumination ×
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          Type C QPO Interpretation
          Image: ESA/NASA/A. Ingram Small scale height, strongly modulated illumination ×
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          Future Directions •  More kinds of variability! – Low-frequency QPOs in neutron stars – High-frequency QPOs in black holes – Kilohertz QPOs in neutron stars •  More data! – RXTE archives – XMM-Newton, NuSTAR – AstroSat – NICER (launch ~April 2017)
          NICER
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          Summary
          •  X-ray binaries are one of the best tools to study matter in strong gravitational fields •  Phase-resolved spectroscopy of QPOs can help break degeneracies between physical models •  Type B QPO in GX 339—4: –  Jet-like precessing region –  arXiv: 1605.01753 •  Type C QPO in GX 339—4: –  Disk-like precessing region –  Paper in prep. GitHub: abigailStev Email: A.L.Stevens@uva.nl Twitter: @abigailStev ✉