A523 Signal Modeling, Statistical Inference and Data Mining in Astrophysics Spring 2011 Lecture 1 • Organization: » Syllabus (text, requirements, topics) » Course approach (goals, themes) • Book: Gregory, “Bayesian Logical Data Analysis for the Physical Sciences” • Heavy use of unpublished notes and articles from the literature • Numerical assignments: you can use your favorite programming language or software package (note no direct use of Mathematica in this course) • Grading: legibility and clear explanations in complete sentences are needed for all submitted homework and papers. • Course meeting times: ok as is? go to MW? Reschedule a makeup day?
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• Many signals are the result of nonlinear operations in natural systems or in apparati
• Many analyses of data are linear operations acting on the data to produce some desired result (detection, modeling)
• E.g. Fourier transform based spectral analysis
• Many analyses are nonlinear • E.g. Maximum entropy and Bayesian
spectral analysis
time
Freq
uenc
y
time
DM
|FFT(f)|
FFT each DM’s time series
1/P2/
P3/
P• • •
Example Time Series and Power Spectrum for a recent PALFA discovery
(follow-up data set shown)
DM = 0 pc cm-3
DM = 217 pc cm-3
Time Series
Where is the pulsar?
Example Time Series and Power Spectrum for a recent PALFA discovery
(follow-up data set shown)
DM = 0 pc cm-3
DM = 217 pc cm-3
Time Series
Here is the pulsar
Spectral analysis as a unifying thread Signals ⇔ Statistics
Spectral analysis: 1. Analysis of variance in a conjugate space
t ↔ f (time and frequency domains) u,v ↔ θ (interferometric images)
• Statistical questions about the nature of the signal in frequency space:
a. Is there a signal? b. What is its frequency? c. What is the shape of the spectrum?
1. Basis functions: Sinusoids t ↔ f Spherical harmonics θ, ϕ ↔ l,m Wavelets time-frequency atoms Principal components the data determine the basis
The appropriate basis (often) is the one that most compactifies the signal in the conjugate domain
Spectral analysis as a unifying thread
Color coded temperature variations of the cosmic microwave background (CMB)
TCMB = 2.7 K
ΔT/TCMB ~ 10-5
Wilkinson Microwave Anisotropy Probe
Basis functions: spherical harmonics
TCMB = 2.7 K
ΔT/TCMB ~ 10-5
Wilkinson Microwave Anisotropy Probe
So we understand the big bang and that there is dark energy
Or maybe not:
“After scrutinizing over seven years’ worth of WMAP data, as well as data from the BOOMERanG balloon experiment in Antarctica, Penrose and Gurzadyn say they have identified a series of concentric circles within the data. These circles show regions in the microwave sky in which the range of the radiation’s temperature is markedly smaller than elsewhere. According to the researchers, the patterns correspond to gravitational waves formed by the collision of black holes in the aeon that preceded our own, and they published these claims in a paper submitted to arXiv” (Physics World).
Galaxy clustering Data from the Sloan Digital Sky Survey
SDSS galaxy distribution (Those with spectra)
Gamma-ray burst locations on the sky
Is there any clustering?
How would you test this?
“Flights within the US were grounded because of the attacks, and incoming international flights were diverted to Canada. Services resumed within a few days but it took years for the market to recover.“
From the BBC web page 04 Sept 2006
Example of a “change point”
Example of a transient event identifiable through data mining of article content:
Is there a periodicity in this time series?
• Repeat for L epochs spanning N=T/P spin periods
• N ~ 108 – 1010 cycles in one year • ⇒ P determined to
Basics of Pulsars as Clocks
• Signal average M pulses • Time-tag using template fitting
P …M×P
W
• J1909-3744: eccentricity < 0.00000013 (Jacoby et al.)
• B1937+21: P = 0.0015578064924327±0.0000000000000004 s
Phase residuals from isolated pulsars after subtracting a quadratic polynomial:
If these pulsars were simply spinning down in a smooth way, we would expect residuals that look like white noise:
Are any of these time series periodic? How can we test for periodicity?
Phase residuals from isolated pulsars after subtracting a quadratic polynomial:
If these pulsars were simply spinning down in a smooth way, we would expect residuals that look like white noise:
For these pulsars, the residuals are mostly caused by spin noise in the pulsar
Are any of these time series periodic? How can we test for periodicity?
Noise in Timing Residuals from G. Hobbs
Long period pulsars
MSPs
How Good are Pulsars as Clocks?
Clock processes are similar to random walks or Brownian motion. What are the best ways to characterize such processes?
Pulsars as Gravitational Wave Detectors
Earth
pulsar
pulses
Gravitational wave background
Gravitational wave background
The largest contribution to arrival times is on the time scale of the total data span length (~20 years for best cases)
MSP J1909-3744 P=3 ms + WD
Jacoby et al. (2005)
Weighted σTOA = 74 ns
Shapiro delay
The best pulsar timing so far:
Correlation Function Between Pulsars
Correlation function of residuals vs angle between pulsars
Example power-law spectrum from merging supermassive black holes (Jaffe & Backer)
Estimation errors from: • dipole term from solar system