Comparing origins of low-frequency quasi-periodic oscillations with spectral-timing

Seminar given at: the Kavli Institute for Theoretical Physics program on accretion disks on January 10 at 2pm, at the Harvard/Smithsonian Center for Astrophysics on January 12 at 11am, and at MIT on January 13 at 2pm.

X-ray spectral-timing is a new field that seeks to investigate how matter behaves in strong gravitational fields. Observations suggest that different types of quasi-periodic oscillations (QPOs) are associated with different emitting-region geometries (e.g. disk-like or jet-like) in the innermost part of the X-ray binary, close to the neutron star or black hole. We developed a technique for phase-resolved spectroscopy of QPOs, and are applying it to Type B and Type C low-frequency QPOs from the black hole X-ray binary GX 339-4. On the QPO time-scale, we find that the energy spectrum changes not only in normalization, but also in spectral shape. We can quantify how the spectral shape changes as a function of QPO phase, and the two different QPOs show markedly different spectral changes. In our previous work, we inferred that the Type B QPO could be caused by a large-scale-height (i.e., jet-like) precessing region illuminating and heating overlapping azimuthal regions of the inner accretion disk. Preliminary results of the Type C QPO indicate that a small-scale-height (disk-like) precessing region may be responsible for the observed spectral changes.

Transcript

1. 
         Comparing origins of low- frequency quasi-periodic oscillations with spectral-timing Abigail Stevens, Phil Uttley University of Amsterdam
2. 
         Outline •  X-ray binaries •  Spectroscopy •  Timing •  Phase-resolved spectroscopy results and interpretation!
        
3. 
         Low-mass X-ray binaries (LMXBs)
         Roche-lobe overflow Accretion disk Compact object Jet Low-mass companion star Figure: ESO/L. Calçada
4. 
         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?
5. 
         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
6. 
         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
7. 
         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
8. 
         Spectra in different accretion states Soft Hard Figure: Done et al 2007
        
9. 
         Black hole spectral states •  Many X-ray binaries are transients: outburst!
         ç Outburst counts light curve é Hardness light curve GX 339—4, Nandi et al 2012 Reviews: Nowak 1995; Remillard & McClintock 2006; Done et al 2007
10. 
          Black hole spectral states •  Many X-ray binaries are transients: outburst!
          Hardness-Intensity diagram ç Outburst counts light curve é Hardness light curve GX 339—4, Nandi et al 2012 Reviews: Nowak 1995; Remillard & McClintock 2006; Done et al 2007 hard low soft high
11. 
          Timing Study light curves in the frequency domain
          1016 1018 1020 1022 1024 5000 104 1.5×104 Count/sec Time (s) Start Time 10168 18:16:52:570 Stop Time 10168 18:17:08:180 Bin time: 0.1562E−01 s Time domain Light curve Frequency/Fourier domain Power density spectrum FOURIER TRANSFORM
12. 
          X-ray variability: Hard to see by eye
          1016 1018 1020 1022 1024 5000 104 1.5×104 Count/sec Time (s) Start Time 10168 18:16:52:570 Stop Time 10168 18:17:08:180 Bin time: 0.1562E−01 s 1700 1702 1704 1706 1708 1710 2000 4000 6000 8000 104 1.2×104 Count/sec Time (s) Start Time 12339 7:28:14:566 Stop Time 12339 7:29:32:683 Bin time: 0.7812E−02 s Light curves
13. 
          X-ray variability: Hard to see by eye
          Noise: Cygnus X-1 Signal: GRS 1915 1016 1018 1020 1022 1024 5000 104 1.5×104 Count/sec Time (s) Start Time 10168 18:16:52:570 Stop Time 10168 18:17:08:180 Bin time: 0.1562E−01 s 1700 1702 1704 1706 1708 1710 2000 4000 6000 8000 104 1.2×104 Count/sec Time (s) Start Time 12339 7:28:14:566 Stop Time 12339 7:29:32:683 Bin time: 0.7812E−02 s Light curves Power density spectra
14. 
          Quasi-periodic oscillations (QPOs)
          Power spectra show amount of variability in a light curve at different frequencies GX 339-4
15. 
          Flashback: BH spectral states
          Hardness-Intensity diagram GX 339-4, Nandi et al 2012 hard low soft high Low-frequency QPOs!
16. 
          BH QPOs and spectral states
          Heil, Uttley, & Klein-Wolt 2015a Hard state HIMS SIMS Soft state Type C QPOs Type B QPOs
17. 
          Binary inclination dependence
          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)
18. 
          Binary inclination dependence
          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) Want to study energy spectra on sub-QPO timescale •  Determine LF QPO emission mechanism •  Different mechanism for Type B vs Type C?
19. 
          Phase-resolved spectroscopy •  New technique allows us to effectively do phase-resolved spectroscopy of QPOs •  Details in paper -- arXiv: 1605.01753
         
20. 
          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
21. 
          Type B QPO spectral variations •  Blackbody variation leads the power-law variation by ~0.3 (110°) •  Power-law: 25% rms variation •  Blackbody: 1.4% rms variation
         
22. 
          Type B QPO interpretation
          Large scale height, weakly modulated illumination ×
23. 
          Type B QPO interpretation
          × Large scale height, weakly modulated illumination
24. 
          Type B QPO interpretation
          × Large scale height, weakly modulated illumination
25. 
          Type B QPO interpretation
          × Large scale height, weakly modulated illumination
26. 
          Ruling out other Type B models •  Intrinsic PL variations reflected in disk? – Phase lag in wrong direction •  Intrinsic disk variations upscattered by PL? – Phase lag (60ms) implies massive distance (1000’s rg) for light travel time •  Propagating fluctuations from disk to PL? – Tiny disk variation couldn’t give such a large PL variation
         
27. 
          •  Different parameter phase relationship •  Power-law: smaller variation (compared to Type B) •  Blackbody: larger variation Type C QPO spectral variations
         
28. 
          Type C QPO interpretation
          Image: ESA/NASA/A. Ingram Small scale height, strongly modulated illumination ×
29. 
          Type C QPO interpretation
          Image: ESA/NASA/A. Ingram Small scale height, strongly modulated illumination ×
30. 
          Type C QPO interpretation
          Image: ESA/NASA/A. Ingram Small scale height, strongly modulated illumination ×
31. 
          Inner region of an LMXB
          Disk Comptonizing region ×
32. 
          Inner region of an LMXB
          Disk × 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 Comptonizing region
33. 
          Inner region of an LMXB
          Disk × 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 Comptonizing region
34. 
          Inner region of an LMXB
          Disk × 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 Comptonizing region
35. 
          Inner region of an LMXB
          Disk × 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 Comptonizing region
36. 
          Inner region of an LMXB
          Disk × 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 Comptonizing region
37. 
          XMM and NuSTAR: H 1743 •  CCD energy resolution: see iron line wiggling •  Method: Ingram & van der Klis 2015 •  Red is phase=0.5, blue is phase=0.75
          10 5 20 50 0.8 1 1.2 ratio Energy (keV) NuSTAR 4 6 8 10 1 1.05 ratio Energy (keV) XMM−Newton Ingram et al. 2016a
38. 
          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) – eXTP (by 2025)
          NICER
39. 
          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 ✉
40. 
         
41. 
          Astrosat •  Launched in Sept 2015 •  3 Large area photon counters – Timing down to ~10 µs – Energy range: 3—80 keV – Larger effective area than RXTE above 15 keV •  Soft X-ray telescope – X-ray CCD detector – Energy range: 0.3—8 keV
          ISRO
42. 
          NICER •  Neutron star Interior Composition ExploreR •  Launch: ~April 2017 •  All-in-one: better timing than RXTE, energy resolution of XMM! •  Attached to space station •  Timing down to 85 ns •  Energy range: 0.2—12 keV
          NASA
43. 
          Cross-correlation function (CCF) •  Cross-correlate a broad reference band with narrow band of interest (energy channel)
          10 2 5 20 1 10 0.2 0.5 2 5 keV2 (Photons cm−2 s−1 keV−1) Energy (keV)
44. 
          Cross-correlation function (CCF) •  Cross-correlate a broad reference band with narrow band of interest (energy channel)
          10 2 5 20 1 10 0.2 0.5 2 5 keV2 (Photons cm−2 s−1 keV−1) Energy (keV)
45. 
          Cross-correlation function (CCF) •  Cross-correlate a broad reference band with narrow band of interest (energy channel)
          10 2 5 20 1 10 0.2 0.5 2 5 keV2 (Photons cm−2 s−1 keV−1) Energy (keV) PCU 2 All other PCUs
46. 
          Cross-correlation function (CCF) •  Cross-correlate a broad reference band with narrow band of interest (energy channel)
          10 2 5 20 1 10 0.2 0.5 2 5 keV2 (Photons cm−2 s−1 keV−1) Energy (keV) PCU 2 All other PCUs Determine relative amplitude and phase of lag of interest band with respect to reference band
47. 
          CCF in 1D •  “Re-creates” relative light curve of QPO in each energy channel •  CCF signal shows an underlying QPO waveform è Do this for all energy channels of the detector 10.5 keV
          Alternative approaches: Miller & Homan 2005; Ingram & van der Klis 2015
48. 
          CCF in 2D
          No counts in this channel
49. 
          CCF in 2D
          No counts in this channel
50. 
          CCF in 2D
          No counts in this channel
51. 
          Lag-energy spectrum Lag in variability at different energies •  Constant slope, smooth: simple component or continuum evolution •  For this data, bump/break in slope!
         
52. 
          Lag-energy fitting
          Simulate timing data with returned spectral parameters, fit lag-energy spectra with original data Good fits: Bad fits:
53. 
          Comparing lag-energy spectra