Upgrade to Pro — share decks privately, control downloads, hide ads and more …

Western University: Mapping Matter in Strong Gr...

Western University: Mapping Matter in Strong Gravity

Colloquium given via Zoom on April 23th, 2020 for Western University.

Title: Mapping Matter in Strong Gravity: Spectral-Timing of Black Holes and Neutron Stars

Abstract: One of the best laboratories to study strong-field gravity is the inner 100s of kilometers around black holes and neutron stars in binary systems with low-mass stars like our Sun. The X-ray light curves of these binary systems show variability on timescales from milliseconds to months — the shorter (sub-second) variability can appear as quasi-periodic oscillations (QPOs), which may be produced by general relativistic effects. My research looks at QPOs from black holes and neutron stars (as well as coherent X-ray pulsations from neutron stars) by fitting the phase-resolved energy spectra of these signals to constrain their physical origin and track their evolution in time. In this talk, I will introduce why black holes and neutron stars are interesting and discuss state-of-the-art “spectral-timing” analysis techniques for understanding more about them. I will also highlight open-source astronomy research software and the importance of mental wellbeing among students and early-career researchers.

Avatar for Dr. Abbie Stevens

Dr. Abbie Stevens

April 23, 2020
Tweet

More Decks by Dr. Abbie Stevens

Other Decks in Science

Transcript

  1. Mapping Matter in Strong Gravity: Spectral-Timing of Black Holes and

    Neutron Stars Dr. Abbie Stevens NSF Astronomy & Astrophysics Postdoctoral Fellow Michigan State University & University of Michigan [email protected] @abigailstev github.com/abigailstev Image: NASA/JPL-Caltech
  2. Outline A.L. Stevens • Michigan State U. & U. Michigan

    § Compact objects, low-mass X-ray binaries § X-ray astronomy: timing, spectroscopy § Quasi-periodic oscillations (QPOs) § STROBE-X: proposed X-ray observatory § Stingray: open-source spectral-timing software Q&A Time #1 Q&A Time #2 Q&A Time #3 2
  3. Outline A.L. Stevens • Michigan State U. & U. Michigan

    § Compact objects, low-mass X-ray binaries § X-ray astronomy: timing, spectroscopy § Quasi-periodic oscillations (QPOs) § STROBE-X: proposed X-ray observatory § Stingray: open-source spectral-timing software 3
  4. Stellar remnants A.L. Stevens • Michigan State U. & U.

    Michigan Image: R.N. Bailey, CC BY 4.0, WikiMedia 2 2 Compact objects 4
  5. § Radius ~ 12 km (7.5 mi), mass ~ 1.5

    MSun § Densityavg. ~ 1014 g/cm3 (the density of an atomic nucleus!) § Surface accelerationgravity ~ 1012 m/s2 § Magnetic field ~ 108 - 1015 Gauss (104-1011 Tesla) § Spin frequencies up to 100’s of Hz Neutron stars (NSs) A.L. Stevens • Michigan State U. & U. Michigan Watts+16 5
  6. Stellar black holes (BHs) § Ultracompact remnant of a massive

    star >20 MSun § Event horizon radius ~15 km for a 10 MSun BH A.L. Stevens • Michigan State U. & U. Michigan 6
  7. A.L. Stevens • Michigan State U. & U. Michigan Image:

    NASA/CXC/M. Weiss Companion star ≲ 1 MSun Hot inner flow/ corona Compact object (BH or NS) Accretion disk Low-mass X-ray binaries How does matter behave in strong gravitational fields? 7
  8. A.L. Stevens • Michigan State U. & U. Michigan Low-mass

    X-ray binaries Image: NASA/CXC/M. Weiss 10 5 20 0.1 1 keV2 (Photons cm−2 s−1 keV−1) Energy (keV) Comptonized blackbody reflection Companion star ≲ 1 MSun Accretion disk Compact object (BH or NS) Hot inner flow/ corona How does matter behave in strong gravitational fields? 8
  9. A.L. Stevens • Michigan State U. & U. Michigan Low-mass

    X-ray binaries Image: NASA/CXC/M. Weiss 1700 1702 1704 1706 1708 1710 2000 4000 6000 8000 104 1.2×104 Count/sec T im e (s) S tart T im e 12339 7:28:14:566 S top T im e 12339 7:29:32:683 B in tim e: 0.7812E −02 s Accretion disk X-ray variability Companion star ≲ 1 MSun Hot inner flow/ corona Compact object (BH or NS) How does matter behave in strong gravitational fields? 9
  10. A.L. Stevens • Michigan State U. & U. Michigan Low-mass

    X-ray binaries Image: NASA/CXC/M. Weiss 10 5 20 0.1 1 keV2 (Photons cm−2 s−1 keV−1) Energy (keV) Comptonized blackbody reflection Companion star ≲ 1 MSun Accretion disk Compact object (BH or NS) Hot inner flow/ corona 1700 1702 1704 1706 1708 1710 2000 4000 6000 8000 104 1.2×104 Count/sec T im e (s) S tart T im e 12339 7:28:14:566 S top T im e 12339 7:29:32:683 B in tim e: 0.7812E −02 s X-ray variability How does matter behave in strong gravitational fields? 10
  11. Outline A.L. Stevens • Michigan State U. & U. Michigan

    § Compact objects, low-mass X-ray binaries § X-ray astronomy: timing, spectroscopy § Quasi-periodic oscillations (QPOs) § STROBE-X: proposed X-ray observatory § Stingray: open-source spectral-timing software 11
  12. X-ray telescopes X-rays UV IR Microwaves Radio Image: Cool Cosmos/Caltech

    X-ray astronomy A.L. Stevens • Michigan State U. & U. Michigan 12
  13. X-ray telescopes: NICER A.L. Stevens • Michigan State U. &

    U. Michigan Image: NASA § Neutron star Interior Composition ExploreR § Launched 3 June 2017, attached to Int’l Space Station § All-in-one: better timing than RXTE and AstroSat, energy resolution of XMM-Newton, high throughput 13
  14. X-ray telescopes: NICER A.L. Stevens • Michigan State U. &

    U. Michigan § Neutron star Interior Composition ExploreR § Launched 3 June 2017, attached to Int’l Space Station § All-in-one: better timing than RXTE and AstroSat, energy resolution of XMM-Newton, high throughput Image: NASA 14
  15. X-ray spectroscopy § X-ray binaries are too small and far

    away for imaging § Like trying to image a human hair on the surface of Mars § Physical processes have characteristic energy distributions § Blackbody, multi-color blackbody § Inverse Compton up-scattering § “Reflection” A.L. Stevens • Michigan State U. & U. Michigan TOTAL COMPTONIZED REFLECTED DISK Image: Gilfanov10 16
  16. X-ray spectroscopy A.L. Stevens • Michigan State U. & U.

    Michigan 0.5 1 1.5 Line profile Gravitational redshift General relativity Transverse Doppler shift Beaming Special relativity Newtonian Eobs/Eem Newtonian Special relativity Transverse Doppler shift Beaming Gravitational redshift Line profile General relativity TOTAL COMPTONIZED REFLECTED DISK 17
  17. “Soft” spectrum: strong accretion disk emission “Hard” spectrum: strong Comptonized

    emission A.L. Stevens • Michigan State U. & U. Michigan Same object, different spectra Images: Done+07; NASA/JPL-Caltech; NASA/GSFC 1000 18
  18. “Soft” spectrum: strong accretion disk emission “Hard” spectrum: strong Comptonized

    emission A.L. Stevens • Michigan State U. & U. Michigan Same object, different spectra Images: Done+07; NASA/JPL-Caltech; NASA/GSFC 1000 19
  19. “Soft” spectrum: strong accretion disk emission “Hard” spectrum: strong Comptonized

    emission A.L. Stevens • Michigan State U. & U. Michigan Same object, different spectra Images: Done+07; NASA/JPL-Caltech; NASA/GSFC 1000 20
  20. “Soft” spectrum: strong accretion disk emission “Hard” spectrum: strong Comptonized

    emission Spectrum changes in “outburst” over weeks to months A.L. Stevens • Michigan State U. & U. Michigan Same object, different spectra Images: Done+07; NASA/JPL-Caltech; NASA/GSFC 1000 21
  21. Fourier transforms A.L. Stevens • Michigan State U. & U.

    Michigan § X-rays from BHs and NSs vary on timescales from microseconds to years § Shorter (< 1 minute) variability: Fourier analysis! § Study time domain f in the frequency domain f § Break down light curve into sine waves, take amplitude of sines at each frequency ^ Problem solution solve (hard) Transformed problem Transformed solution solve (easy) Fourier transform inverse Fourier transform Image: L. Barbosa via wikiMedia 22
  22. Applying Fourier transforms to data 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 FO U R IE R TRANSFORM2 A.L. Stevens • Michigan State U. & U. Michigan Light curve broken into equal-length chunks (64 seconds), take power spectrum of each chunk, average those together 23
  23. X-ray variability: Hard to see by eye 1014 1016 1018

    1020 1022 5000 104 1.5×104 Count/sec Time (s) CYGNUS_X−1 Start Time 10168 18:16:52:578 Stop Time 10168 18:17:02:547 Bin time: 0.3125E−01 s A.L. Stevens • Michigan State U. & U. Michigan 1696 1698 1700 1702 1704 4000 5000 6000 7000 Count/sec Time (s) GRS1915+105 Start Time 12339 7:28:14:582 Stop Time 12339 7:28:24:542 Bin time: 0.4000E−01 s Light curves Power density spectra Noise: Cygnus X-1 Signal: GRS 1915+105 24
  24. Q&A Time #1: § Compact objects § X-ray binaries §

    X-ray observations § General spectral analysis § General timing analysis A.L. Stevens • Michigan State U. & U. Michigan 25
  25. Outline A.L. Stevens • Michigan State U. & U. Michigan

    § Compact objects, low-mass X-ray binaries § X-ray astronomy: timing, spectroscopy § Quasi-periodic oscillations (QPOs) § STROBE-X: proposed X-ray observatory § Stingray: open-source spectral-timing software 26
  26. Strohmayer ‘01 § High-frequency: 100’s Hz § Hot blobs in

    Keplerian orbit at inner disk edge? § Low-frequency: ~0.1-10’s Hz § Precession of corona/hot flow? Magnetic warps in disk? Comptonized disk fluctuations? A.L. Stevens • Michigan State U. & U. Michigan Quasi-periodic oscillations (QPOs) 27
  27. QPOs → Damped harmonic oscillators A.L. Stevens • Michigan State

    U. & U. Michigan y = cos(⍵t) x e-bt b=0 b=0.08 29
  28. QPOs → Damped harmonic oscillators A.L. Stevens • Michigan State

    U. & U. Michigan y = cos(⍵t) x e-bt b=0 b=0.08 b=0.22 30
  29. QPOs → Damped harmonic oscillators A.L. Stevens • Michigan State

    U. & U. Michigan y = cos(⍵t) x e-bt b=0 b=0.08 b=0.22 b=0.5 31
  30. QPOs → Damped harmonic oscillators A.L. Stevens • Michigan State

    U. & U. Michigan y = cos(⍵t) x e-bt b=0 b=0.08 b=0.22 b=0.5 b=1.0 The stronger the damping, the wider the peak 32
  31. QPOs → Damped harmonic oscillators A.L. Stevens • Michigan State

    U. & U. Michigan y = cos(⍵t) x e-bt The stronger the damping, the wider the peak Astrophysics: What is the cause of the oscillation? What is the cause of the damping/dissipation? What else are we not accounting for? b=0 b=0.08 b=0.22 b=0.5 b=1.0 33
  32. LF QPOs: Lense-Thirring precession? A.L. Stevens • Michigan State U.

    & U. Michigan Stella+Vietri ‘98; Fragile+Anninos ‘05; Schnittman, Homan+Miller ‘06; Ingram+09; Ingram+van der Klis ‘15; Fragile+16; Ingram+16a,b; Liska+18 Lense-Thirring precession/frame dragging with nodal precession Movie: L. Stein 34
  33. LF QPOs: Lense-Thirring precession? × A.L. Stevens • Michigan State

    U. & U. Michigan Hot inner flow (Comptonizing region) Accretion disk Disk color pattern: Doppler shifting and boosting of emission Stella+Vietri ‘98; Fragile+Anninos ‘05; Schnittman, Homan+Miller ‘06; Ingram+09; Ingram+van der Klis ‘15; Fragile+16; Ingram+16a,b; Liska+18 35
  34. LF QPOs: Lense-Thirring precession? A.L. Stevens • Michigan State U.

    & U. Michigan See recent work by: Chattarjee, Liska, Markoff, Tchekhovskoy Movie: A. Tchekhovskoy × 36
  35. LF QPOs: Lense-Thirring precession? × A.L. Stevens • Michigan State

    U. & U. Michigan Expect changing energy spectrum on sub-QPO timescale: • Normalization • Blackbody • Iron line profile Want to: • Determine low-freq. QPO emission mechanism • Different mechanism for QPO types? 37
  36. Quasi-periodic signals: § not coherent enough to fold light curve

    § in time domain, signal would smear out! è average together signals in frequency domain § ephemeris not needed Phase-resolved spectroscopy Periodic signals: § fold light curve at pulse period, stack signal in time domain § need to know ephemeris of source See Miller+Homan ‘05; Ingram+van der Klis ‘15; Stevens+Uttley ‘16 A.L. Stevens • Michigan State U. & U. Michigan 38
  37. A.L. Stevens • Michigan State U. & U. Michigan Power

    (rms2/Hz) Elapsed time (in 64 s segments) NICER observations of MAXI J1535 Stevens+18 Dynamical power spectrum: evolution of power spectrum in time 39
  38. Power (rms2/Hz) Elapsed time (in 64 s segments) Broadband/band-limited noise

    Low-freq. QPO QPO harmonic Low-amplitude low-freq. QPO hiding here? A.L. Stevens • Michigan State U. & U. Michigan NICER observations of MAXI J1535 Dynamical power spectrum: evolution of power spectrum in time 40 Stevens+18
  39. Power (rms2/Hz) Elapsed time (in 64 s segments) A.L. Stevens

    • Michigan State U. & U. Michigan NICER observations of MAXI J1535 Yes! Needed to average together data segments for it to be visible. QPO Harmonic Broadband noise Dynamical power spectrum: evolution of power spectrum in time 41 Stevens+18
  40. MAXI J1535 phase spectra A.L. Stevens • Michigan State U.

    & U. Michigan § Ratio of QPO- phase-resolved spectra with the mean spectrum → how spectral components vary with QPO phase § ~25% phase lag gives it the “doing the wave” appearance Stevens+ in prep. 42
  41. MAXI J1535 phase spectra A.L. Stevens • Michigan State U.

    & U. Michigan § Ratio of QPO- phase-resolved spectra with the mean spectrum → how spectral components vary with QPO phase § ~25% phase lag gives it the “doing the wave” appearance Stevens+ in prep. § Compared with previous “Type B” QPO: predict tall jet-like emitting region § But, lag sign is opposite and binary has different inclination! § Compact, smaller scale- height emitting region Image: Ingram+09 43
  42. LF QPOs linked to discrete jet ejecta A.L. Stevens •

    Michigan State U. & U. Michigan § Transition between 2 types of LF QPOs (along with broadband spectral changes) correlates with radio jet “turning off” and discrete jet ejecta § Long suspected! Radio flare within ~day of QPOs for 6 BHs studied in Fender+09, Miller-Jones+12, Russell+19 § MAXI J1820+070 (right): Type-B QPO turning off at start of flare (using NICER, AMI-LA) Homan+20 (incl. ALS) 44
  43. LF QPOs linked to discrete jet ejecta A.L. Stevens •

    Michigan State U. & U. Michigan § Transition between 2 types of LF QPOs (along with broadband spectral changes) correlates with radio jet “turning off” and discrete jet ejecta § Long suspected! Radio flare within ~day of QPOs for 6 BHs studied in Fender+09, Miller-Jones+12, Russell+19 § MAXI J1820+070 (right): Type-B QPO turning off at start of flare (using NICER, AMI-LA) Homan+20 (incl. ALS) § QPO emission mechanism/region closely connected with jet emission region (see Homan+20, incl. ALS) § Meg Davis tried phase-resolving the “Type B” QPO (purple arrow) to dig deeper, too low amplitude for full phase-resolved spectroscopy 45
  44. Q&A Time #2: § QPOs (quasi-periodic oscillations) § Emission mechanisms

    like precession § Observational and analytical techinques A.L. Stevens • Michigan State U. & U. Michigan 46
  45. Outline A.L. Stevens • Michigan State U. & U. Michigan

    § Compact objects, low-mass X-ray binaries § X-ray astronomy: timing, spectroscopy § Quasi-periodic oscillations (QPOs) § STROBE-X: proposed X-ray observatory § Stingray: open-source spectral-timing software 47
  46. Future X-ray telescope: A.L. Stevens • Michigan State U. &

    U. Michigan X-ray Concentrator Array (0.2-12 keV) Wide Field Monitor (2-50 keV) Large Area Detector (2-30 keV) Solar panels RXTE Electronics, antenna, etc. See Ray+18 (incl. ALS) 48
  47. A.L. Stevens • Michigan State U. & U. Michigan RXTE

    Electronics, antenna, etc. Science drivers: spin distribution of BHs, accretion disk winds, disk-jet connection, NS equation of state, burst oscillations, GRBs, LIGO EM counterparts, TDEs, discovering new sources, etc! Video from NASA Mission Design Lab, April 2018 § Combines strengths of NICER and LOFT: high throughput X-ray timing with good spectroscopy § All components already at high tech. readiness level § Highly modular design Future X-ray telescope: 49
  48. A.L. Stevens • Michigan State U. & U. Michigan RXTE

    Electronics, antenna, etc. Science drivers: spin distribution of BHs, accretion disk winds, disk-jet connection, NS equation of state, burst oscillations, GRBs, LIGO EM counterparts, TDEs, discovering new sources, etc! Video from NASA Mission Design Lab, April 2018 For my research: <1ms time resolution + CCD energy resolution + soft X-ray coverage è Resolve how physical components vary, where they’re located § Combines strengths of NICER and LOFT: high throughput X-ray timing with good spectroscopy § All components already at high tech. readiness level § Highly modular design Future X-ray telescope: 50
  49. Outline A.L. Stevens • Michigan State U. & U. Michigan

    § Compact objects, low-mass X-ray binaries § X-ray astronomy: timing, spectroscopy § Quasi-periodic oscillations (QPOs) § STROBE-X: proposed X-ray observatory § Stingray: open-source spectral-timing software 51
  50. § Open-source timing and spectral-timing software (Astropy affiliated package!) §

    Stingray: Python library of analysis tools § HENDRICS: shell scripting interface § DAVE: graphical user interface § Tutorials in Jupyter(/iPython) notebooks § Well-documented, automated unit tests, 95% test coverage § Huppenkothen, Bachetti, ALS+2019, ApJ & JOSS § Google Summer of Code students in 2016-2020 (including S. Sharma* in 2018) Stingray A.L. Stevens • Michigan State U. & U. Michigan StingraySoftware.github.io * Student mentored by ALS 52
  51. Mental wellbeing is important A.L. Stevens • Michigan State U.

    & U. Michigan § There is a mental health crisis among academics § ~1/3 of grad students meet criteria for depression § Gender minorities had much higher rates of problems than cis-men § Work and organizational context (incl. satisfaction with advising and work environment) are significant predictors of mental health § Stats, tools, resources: abigailstevens.com/mental- wellbeing-academia § Be aware, take care of yourself, look out for friends and colleagues 53
  52. Summary GitHub: abigailStev Email: [email protected] Twitter: @abigailStev ✉ A.L. Stevens

    • Michigan State U. & U. Michigan § X-ray binaries are awesome! One of the best tools to study matter in strong gravitational fields § Use X-ray spectral-timing analysis to decipher emission mechanisms for rapid variability § Low-freq. quasi-periodic oscillations: precessing hot inner flow/base of jet? § Variability transitions linked to discrete jet ejecta § NICER: soft X-ray telescope on International Space Station § STROBE-X: proposed large-area X-ray observatory § Stingray: github.com/ StingraySoftware