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Time series exploration with Stingray

Time series exploration with Stingray

Invited talk given remotely at the 9th Microquasar Workshop: https://sites.google.com/inaf.it/microquasar-2020/home

Abstract:
New ideas about how to analyze time-domain X-ray astronomy data have initiated the “spectral-timing revolution,” leading to a surge in developments of analysis techniques. Many individual tools and libraries exist, and some are even publicly available, but we lacked a coherent set for a complete analysis that provides documentation and tutorials of the techniques themselves, not just the syntax for implementation. Stingray is a community-developed, open-source software package in Python for spectral-timing analysis of astrophysical data. This code provides a library of spectral-timing analysis tools while following the Astropy guidelines for modern open-source scientific software development. Our aim is to provide the community with a package that eases the learning curve for state-of-the-art spectral-timing techniques, with a correct statistical framework, to make maximal use of data from NuSTAR, NICER, and potentially STROBE-X and eXTP. In this talk, I will review the spectral-timing analysis tools in the Stingray library and show examples from ongoing research. For more information on Stingray, see: https://stingray.science

More about Dr. Abbie Stevens: https://abigailstevens.com/

Dr. Abbie Stevens

September 22, 2021
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Transcript

  1. Abbie Stevens, on behalf of Stingray contributors and developers
    Various astronomy things in the state of Michigan
    Instructor in general sciences, paused NSF A&A postdoc fellow
    [email protected]
    @abigailstev
    github.com/abigailstev
    Time series exploration
    with Stingray

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  2. Features in X-ray light curves
    Strohmayer 01
    Abbie Stevens • Michigan State U. & U. Michigan
    § Coherent pulsations from NSs
    ⇾ Burst oscillations, spin-up, spin-down, glitches, transition/switching
    § Quasi-periodic oscillations (QPOs) from BHs and NSs
    ⇾ Low-freq. (~0.1-20 Hz): Precession of corona/hot flow? Magnetic warps in
    disk?
    ⇾ High-freq. (~100-1000 Hz): Hot blobs in Keplerian orbit at inner disk edge?
    Radial oscillations in NS boundary layer?
    § Broadband/band-limited noise at ≲ 1 Hz
    Stevens

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  3. Fourier transforms (for evenly sampled data)
    § X-ray light curves of 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
    ^
    Image: L. Barbosa via wikiMedia
    Abbie Stevens • Michigan State U. & U. Michigan

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  4. But it’s not just X-ray data!
    Abbie Stevens • Michigan State U. & U. Michigan
    § A.Tetarenko+21: Multi-
    wavelength fast timing in
    radio, sub-mm, optical, and
    X-ray
    § Paice+21: optical/X-ray lags
    § Kimura+21: power spectra
    of a dwarf nova in a CV
    § Crinquand+21: power
    spectra of γ-ray light curves
    from 2D GR-PIC
    § Nimmo+21: FRB repeaters

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  5. Slide adapted from J. VanderPlas
    SciPy
    Why Python?
    Abbie Stevens • Michigan State U. & U. Michigan

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  6. Stingray core library
    § Library of time series analysis methods
    ⇾Light curve manipulation, GTIs
    ⇾Power spectra, cross spectra, bispectra
    ⇾Lag-frequency & lag-energy spectra
    ⇾Rms & covariance spectra
    ⇾Coherence, cross-correlation
    ⇾Phase-resolved spectroscopy of QPOs
    ⇾Pulsation searches
    Abbie Stevens • Michigan State U. & U. Michigan

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  7. Stingray core library
    Abbie Stevens • Michigan State U. & U. Michigan
    § Library of time series analysis methods
    § Simulation tools
    ⇾Timmer & Koenig power spectra
    ⇾Pulsations
    ⇾Impulse response, 2D transfer functions

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  8. Stingray core library
    Abbie Stevens • Michigan State U. & U. Michigan
    § Library of time series analysis methods
    § Simulation tools
    § Modeling tools
    ⇾Power spectra, cospectra: pulsations, QPOs, noise
    • Built on scipy and emcee, including Laplace distribution for
    cospectra (Huppenkothen+Bachetti 18)
    • Integrating with Astropy.modeling
    ⇾Bayesian parameter estimation, maximum likelihood

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  9. § Inform at which frequencies the light curve is varying
    Plots courtesy of M. Brumback
    Power spectra (periodograms)
    Abbie Stevens • Michigan State U. & U. Michigan

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  10. NICER data of BH
    MAXI J1631-479
    from 2019
    (sudden jumps are gaps due to spacecraft orbit)
    Stevens
    Transition to
    intermediate
    state, Type C
    QPO appears!
    Dynamical power spectra (spectrograms)
    Abbie Stevens • Michigan State U. & U. Michigan

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  11. § Can get around timing systematics in NuSTAR with cospectra!
    § Cross spectrum and its products like the cospectra are used
    extensively in spectral-timing analysis
    Huppenkothen+Bachetti 18
    Bachetti+Huppenkothen 18
    Cospectra
    Abbie Stevens • Michigan State U. & U. Michigan

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  12. § Can get around timing systematics in NuSTAR with cospectra!
    § Cross spectrum and its products like the cospectra are used
    extensively in spectral-timing analysis
    Huppenkothen+Bachetti 18
    Bachetti+Huppenkothen 18
    Cospectra
    Abbie Stevens • Michigan State U. & U. Michigan

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  13. Fractional covariance
    NuSTAR data of a pulsar from Stevens+in prep
    § Fractional variance
    ⇾ rms: of one light curve
    (Revnivtzev+99)
    ⇾ covariance: of one with
    respect to a reference light
    curve (Wilkinson+Uttley 09)
    § Energy resolution of the
    light curve energy bands
    (often binned up to be
    broader than detector
    resolution)
    § [Full disclosure: this feature needs
    more testing!]
    RMS and covariance spectra
    Abbie Stevens • Michigan State U. & U. Michigan

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  14. § Stingray.modeling has
    range of statistical
    models for Gaussian,
    Poisson, χ2, and Laplace
    distributed data
    QPO
    Harmonic
    Broadband noise
    MAXI J1535-571
    Stevens+18
    Modeling power spectra
    Abbie Stevens • Michigan State U. & U. Michigan

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  15. § Stingray.modeling has
    range of statistical
    models for Gaussian,
    Poisson, χ2, and Laplace
    distributed data
    QPO
    Harmonic
    Broadband noise
    MAXI J1535-571
    Huppenkothen+19
    Modeling power spectra
    Abbie Stevens • Michigan State U. & U. Michigan
    Figure 4. from Stingray: A Modern Python Library for Spectral Timing
    null 2019 APJ 881 39 doi:10.3847/1538-4357/ab258d
    http://dx.doi.org/10.3847/1538-4357/ab258d
    © 2019. The American Astronomical Society. All rights reserved.

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  16. § Simulates power spectra with specific shapes (white noise, red noise,
    broadband noise, QPO)
    § Can be used to estimate errors on power spectra
    § Warning: does not preserve energy-dependent phase relationships!
    Though energy channels are supported
    Flicker noise Poisson noise
    Brightness
    Time Time
    Example in the literature:
    K2 data of PSR J1023 orbit
    Kennedy+18
    Also have more
    sophisticated
    simulation tools
    with impulse
    response
    functions!
    Figures from Stingray docs
    Timmer & Koenig simulations
    Abbie Stevens • Michigan State U. & U. Michigan

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  17. Lead: M. Bachetti
    § Evolution of MaLTPyNT,
    analysis software for
    NuSTAR timing
    Stingray + HENRICS + DAVE
    Abbie Stevens • Michigan State U. & U. Michigan

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  18. Stingray + HENRICS + DAVE
    Abbie Stevens • Michigan State U. & U. Michigan

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  19. HENDRICS: Interactive phaseograms
    Abbie Stevens • Michigan State U. & U. Michigan
    null 2019 APJ 881 39 doi:10.3847/1538-4357/ab258d
    http://dx.doi.org/10.3847/1538-4357/ab258d
    © 2019. The American Astronomical Society. All rights reserved.
    Huppenkothen+19
    Times Of Arrival can
    be exported for use
    with pulsar timing
    software like PINT
    or Tempo2

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  20. Data
    Analysis
    for
    Variable
    Events
    Leads:
    P. Balm,
    S. Migliari
    Image from M. Bachetti
    Stingray + HENRICS + DAVE
    Abbie Stevens • Michigan State U. & U. Michigan

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  21. Data
    Analysis
    for
    Variable
    Events
    Stingray + HENRICS + DAVE
    Abbie Stevens • Michigan State U. & U. Michigan
    Figure 7. from Stingray: A Modern Python Library for Spectral Timing
    null 2019 APJ 881 39 doi:10.3847/1538-4357/ab258d
    http://dx.doi.org/10.3847/1538-4357/ab258d
    © 2019. The American Astronomical Society. All rights reserved.
    Huppenkothen+19
    Leads:
    P. Balm,
    S. Migliari
    See also: Migliari+20, ASPC

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  22. Documentation
    Abbie Stevens • Michigan State U. & U. Michigan
    We also have Jupyter notebook tutorials:
    github.com/StingraySoftware/notebooks

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  23. Get involved with Stingray!
    Abbie Stevens • Michigan State U. & U. Michigan
    We also have a Slack
    workspace for discussing
    features and troubleshooting

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  24. § Conferences:
    ⇾ Python in Astronomy conference series
    ⇾ AstroHackWeek, .Astronomy
    ⇾ Special sessions at large symposia
    ⇾ Hack days at AAS, EWASS
    § Training:
    ⇾ Software Carpentry and Data Carpentry workshops
    ⇾ Paid summer internships via Google Summer of Code (Bachelors)
    ⇾ LSSTC Data Science Fellowship Program (Masters and PhD)
    § Databases and affiliations:
    ⇾ Astrophysical Source Code Library: ascl.net
    ⇾ Astropy affiliated packages: astropy.org/affiliated
    Facilitating astro research software
    Abbie Stevens • Michigan State U. & U. Michigan

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  25. Following best practices for software
    If what you want isn’t already out there:
    § Open-source with version control (on, e.g., GitHub) AND LICENSED!
    § Documentation on how to implement the code *and* what the physics is (cite
    papers in the docs)
    § Tutorials with examples of standard use cases
    § Able to be imported into our existing codes in python (though could use a python
    wrapper around, e.g., C or Fortran)
    § Able to run on a standard/nice desktop computer
    § Plausible that a sysadmin for a university-level computing cluster will install the
    necessary dependencies so you can run it there for more/faster analysis, fitting,
    etc.
    § Accompanying paper for proper citation and credit
    Abbie Stevens • Michigan State U. & U. Michigan

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  26. § Stingray is a tool for timing and spectral-timing analysis of
    interesting astronomical time series
    ⇾ Stingray version 0.3 was released on June 1st, 2021
    ⇾ HENDRICS version 6.0 released on May 31st, 2021
    § Install instructions: docs.stingray.science/
    § Code & tutorials: github.com/StingraySoftware
    —Papers: Huppenkothen, Bachetti, ALS+2019, ApJ & JOSS
    —Cite scientific papers in code documentation
    —Software is vital for the future of astronomy
    Summary
    Abbie Stevens • Michigan State U. & U. Michigan

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