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

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

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

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

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

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

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

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

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

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

§ 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

§ 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

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

§ 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

§ 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.

§ 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

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

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

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

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

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

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

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

§ 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

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

§ 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