LIGO's First Observing Run: Gravitational-Wave Astronomy on the Rise Chris Pankow (CIERA / Northwestern University) on behalf of the LIGO Scientific Collaboration and Virgo Collaboration LIGO-G1602321 Miami2016, December 19 th 2016 GW Available in this Talk
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LIGO's First Observing Run: Gravitational-Wave …s First Observing Run: Gravitational-Wave Astronomy on the Rise Chris Pankow (CIERA / Northwestern University) on behalf of the …
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LIGO's First Observing Run: Gravitational-Wave Astronomy on the Rise
Chris Pankow (CIERA / Northwestern University) on behalf of the LIGO Scientific Collaboration and Virgo Collaboration
LIGO-G1602321Miami2016, December 19th 2016
GW Available in this Talk
O1 BBH Events2
“Chirps” in the time domain (monotonically increasing in frequency vs time)
Lower mass → Higher frequency content / longer “in band”
Parameter Posteriors: Form the posterior on a given parameter set
μ from Bayes’ Law
Bayes Factor: Often overlooked (posterior distributions normalized
manually) but encodes the Bayesian signal vs. noise
comparison
PE Method 1: 15+ dimensional space explored by Markov-Chain Monte Carlo. Parallel tempering: ΛT added for more efficient convergence time. Determine “convergence” by number
of effective, uncorrelated samples drawn using the autocorrelation length
Bayesian Parameter Estimation5
Parameter Posteriors: Form the posterior on a given parameter set
μ from Bayes’ Law
Bayes Factor: Often overlooked (posterior distributions normalized
manually) but encodes the Bayesian signal vs. noise
comparison
PE Method 2: ”Nested Sampling”; swarm of points exploring the likelihood space and estimating the integrand. Allows better estimation of the evidence integral p(d) and thus for
comparisons of signal vs. Gaussian noise hypothesis
BBH Masses and Spins6
Parameter Degeneracies: Primarily sensitive to the chirp mass
— leaves large degeneracies along contours of chirp mass
(GW151226 approaching m2 < 3 region)
Frequency content (and thus “length in band” affected by both effective spin and mass
Dealing with Multiple Event Categories:Being unsure of the intrinsic source populations and origins, we calculate the event rates for
all three events and take the union to derive the overall event rate of BBH coalescence. Also test distributions of events according to uniform in the logarithm of component mass
and according to the stellar initial mass function: p(m1) ∝ m12.35
Dealing with Multiple Event Categories:Being unsure of the intrinsic source populations and origins, we calculate the event rates for
all three events and take the union to derive the overall event rate of BBH coalescence. Also test distributions of events according to uniform in the logarithm of component mass
and according to the stellar initial mass function: p(m1) ∝ m12.35
• Long delay times disfavored, but metallicity at higher redshifts (and hence tau) is smaller (e.g. star formation rate thought to peak at z~2) Tension?
• A few more events could allow us to distinguish R(z), at least R(z) ~ uniform versus other hypotheses
• Eccentricity: order of magnitude arguments constrain in-band eccentricity to less than 0.1
• Sources expected to circularize via GW radiation before entering the LIGO band
• Only beginning to develop template families to deal with this — first line of defense nominally handled by generic transient searches
• Extensive EM facility coordination — multimessenger astronomy will soon be a reality
• Host identification can allow for independent measurement of H0
• In 2018 GW150914 triples in SNR, possibly a SNR of 100 with four detectors
• Detailed catalog of sources parlay into source formation models and clearer understanding of compact object formation, low metallicity environments, and XRB dynamics
• Exquisitely precise tests of general relativity
• 2018: BBH / day? plus likely detections of NSBH and BNS (several / mo or more)
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Finally...25
A. Simonnet (Sonoma State)
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