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.

Transcript

1. Compact Objects:
   Science, Software, and Outreach
   Dr. Abbie Stevens
   NSF Astronomy & Astrophysics Postdoctoral Fellow
   Michigan State University & University of Michigan
   alstev@msu.edu
   @abigailStev
   github.com/abigailStev
   Image: NASA/JPL-Caltech
   

   View Slide

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
   

   View Slide

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?
   

   View Slide

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
   

   View Slide

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
   

   View Slide

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

   View Slide

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!
   

   View Slide

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)
   

   View Slide

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
   

   View Slide

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
    

    View Slide

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
    

    View Slide

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!
    

    View Slide

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
    

    View Slide

14. Summary
    GitHub: abigailStev
    Email: alstev@msu.edu
    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