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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


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

    See recent work by: Chattarjee, Liska, Markoff, Tchekhovskoy Movie: A. Tchekhovskoy × 6
  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!
  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)
  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
  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
  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
  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!
  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
  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