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Compact Objects: Science, Software, and Outreach

Compact Objects: Science, Software, and Outreach

This talk was given at the NSF Astronomy & Astrophysics Postdoctoral Fellowship virtual symposium on February 10, 2021. Note that gifs and videos won't render in this pdf.

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 systems show variability on timescales from milliseconds to months — the rapid 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 by applying state-of-the-art “spectral-timing” techniques to constrain the physical origin of these signals. Here I will present the three facets of compact objects in my NSF fellowship: scientific results, the Stingray open-source spectral-timing software package, and doing outreach with school classes in these COVID times.

Dr. Abbie Stevens

February 10, 2021
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  1. Compact Objects:
    Science, Software, and Outreach
    Dr. Abbie Stevens
    NSF Astronomy & Astrophysics Postdoctoral Fellow
    Michigan State University & University of Michigan
    [email protected]
    @abigailStev
    github.com/abigailStev
    Image: NASA/JPL-Caltech

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  2. Abbie Stevens • MSU & UMich
    Low-mass X-ray binaries
    Image: NASA/CXC/M. Weiss
    10
    5 20
    0.1 1
    keV2 (Photons cmï2 sï1 keVï1)
    Energy (keV)
    Comptonized
    blackbody
    reflection Accretion disk
    Companion
    star ≲ 1 MSun
    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
    ï02
    s
    X-ray variability
    How does matter behave in strong gravitational fields?
    2

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  3. Abbie Stevens • MSU & UMich
    Quasi-periodic oscillations (QPOs)
    3
    GX 339-4
    Power ([rms/mean]2)
    § Low-frequency QPOs (~0.1-20 Hz): Precession of
    corona/hot inner flow? Magnetic warps in disk?

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  4. LF QPOs: Lense-Thirring precession?
    Abbie Stevens • MSU & UMich
    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
    4

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  5. LF QPOs: Lense-Thirring precession?
    ×
    Abbie Stevens • MSU & UMich
    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
    5
    Movie: A. Ingram

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  6. LF QPOs: Lense-Thirring precession?
    Abbie Stevens • MSU & UMich
    See recent work by:
    Chattarjee, Liska,
    Markoff,
    Tchekhovskoy
    Movie: A. Tchekhovskoy
    ×
    6

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  7. LF QPOs: Lense-Thirring precession?
    ×
    Abbie Stevens • MSU & UMich
    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?
    7
    Takeaway:
    A geometric precession mechanism like Lense-Thirring fits the data!
    (Stevens+Uttley16, Stevens+18)
    Next:
    Same for neutron star low-freq. QPOs?
    Fit with magnetically-supported spiral arm structure predictions
    Phase-resolved spectroscopy of quasi-periodic oscillations!

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  8. LF QPOs linked to discrete jet ejecta
    Abbie Stevens • MSU & UMich
    § Transition between types of
    LF QPOs (turquoise and
    purple) correlates with radio
    jet “turning off” (red) and
    discrete jet ejecta (blue)
    § Long suspected! Radio flare
    within ~day of QPOs
    (Fender+09, Miller-Jones+12, Russell+19)
    § MAXI J1820+070:
    Type-B QPO turning off at
    start of flare
    Homan+20 (incl. ALS) 8
    § QPO emission mechanism/region
    closely connected with jet emission
    region (see Homan+20, incl. ALS)
    § We tried phase-resolving the “Type
    B” QPO (purple arrow) to dig
    deeper, too low amplitude for full
    phase-resolved spectroscopy
    (see Davis & Stevens 2020, RNAAS)

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  9. NICER: soft X-ray telescope
    Abbie Stevens • MSU & UMich
    § Neutron star Interior Composition ExploreR
    § Launched in 2017, attached to Int’l Space Station
    § All-in-one: 100ns timing resolution, CCD energy
    resolution in 0.2-12 keV, high throughput for bright
    sources
    Image:
    NASA
    9

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  10. Future X-ray telescope:
    Abbie Stevens • MSU & UMich
    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)
    10
    Proposed
    Probe-class
    mission to the
    Astro2020
    Decadal Survey
    Effective area >5 m2 @ 6 keV
    1 10
    0.1

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  11. Abbie Stevens • MSU & UMich
    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:
    11
    For my research: <1ms time resolution + CCD
    energy resolution + soft X-ray coverage è Resolve
    how physical components vary, where they’re located

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  12. § 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 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
    Abbie Stevens • MSU & UMich
    StingraySoftware.github.io
    * Student mentored by ALS
    12
    Please remember to name and
    cite software in your papers!

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  13. Virtual school visits
    § Kids think black holes are cool!
    § 30-60 minutes
    § What is astronomy?
    § Presentation on how scientists
    “see” black holes
    - X-ray binaries
    - Tidal disruption events
    - Event Horizon Telescope
    - Orbital motion of stars near Sgr A*
    - LIGO & Virgo
    - Gravitational lensing
    § Q&A
    Abbie Stevens • MSU & UMich 13
    Video: NASA/GSFC/J. Schnittman

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  14. Summary
    GitHub: abigailStev
    Email: [email protected]
    Twitter: @abigailStev

    Abbie Stevens • MSU & UMich
    § X-ray binaries are awesome! One of the best tools to
    study matter in strong gravitational fields
    § 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 the ISS
    § STROBE-X: proposed large-area X-ray observatory
    § Stingray: github.com/
    StingraySoftware
    § Virtual classroom visits via
    Skype A Scientist and
    MSU SciFest

    View Slide