=== Andrea Lommen - pulsar timing overview === - NANO-Grav: North American Nano-Hertz Observatory of Gravitational Waves - Arecibo, Green Bank... later ATA - Falsification of 3C 66B 10^10 Msun BH binary - Monte Carlo simulation to yield upper limit for stochastic background - 10000 GWs with amplitude randomly generated as member of a model spectrum - Spectrum by interpolation + double differencing + FFT - Ask not: what is the minimum amplitude required to detect background 95% of time - Ask: what is the value of A that leads to the conclusion that background is absent 95% of the time - Limit places an interesting constraint on SMBH population - Equal to Wyithe and Loeb (2003), larger than Jaffe Backer (2005) and Enoki (2004) - Pulsar response to standard and longitudinal polarization modes (best way to measure polarization) - Directional burst detection also possible with pulsar correlations === Vuk Mandic - stochastic background sources === === Tania Regimbau - astrophysical sources of stochastic gravitational-wave backgrounds === - astrophysical vs. cosmological backgrounds - spectral properties; duty cycle = event duration / time interval - D << 1: burst data-analysis, optimal filtering - D ~ 1: maximum likelihood statistic, probability event horizon - D >> 1 (Gaussian): cross-correlation statistic --> Inspiral session <-- === Chris Messenger - stochastic template placement === - matched filtering requires prior waveform knowledge - CPU limited parameter-space exploration - need efficient template placement - metric: construct a measure of distance in parameter space equivalent to signal-template overlap - use eigensystem to define local unit and directions - in globally flat spaces, get mathematical covering problem - simplest n-dimensional lattice is cubic; "best known" is A_n for n < 24 (hexagonal basic cell in 2D) - lattice normalized thickness theta = R^n = sqrt(|g_ij|); theta is proportional to number of templates - random template placement: - place single template; what is probability that it's outside a distance circle? 1 - V_n R^n / V_s - derive probability of achieving mismatch mu: P' = 1 - (1 - V_n R^n)^N / V_s^N - the covering is never total for any number of templates - random covering has better theta than lattices at 10 dimensions if a little covering can be sacrificed: lattices go to a lot of effort to cover last few % of space - can we use "lazy" lattices? Yes, but random covering still beats cubic - for nonflat spaces, need only to control the determinant of the metric: - generate template density function, use it to fill parameter space - but placing random bank is far simpler than lattice - all searches are statistical anyway - Stas: explore ambiguity function to decide random bank placement === Drew Keppel - improvements to LSC binary inspiral search === - so far: - investigation of SPA templates up to 35 Msun - using nonspinning for somewhat spinning - using circular for eccentric - for S5: - 2PN SPA for low-mass region, component masses 1-34 Msun, maximum M = 35 Msun, cutoff at ISCO - 2PN EOB time-domain for high-mass, component masses 1-99 Msun, total mass 25-100 Msun, cutoff at light ring - background triggers are very different in BNS and BBH mass regions: higher effective SNR for the latter - estimate background using nonphysical time-slide coincidences: excess of H1H2L1 background by sliding H1 and H2 separately - new clustering and coincidence based on template-placement metric === Lucia Santamaria - Including information from numrel into inspiral searches === - numrel: breakthrough in 2005; stable, accurate codes producing waveforms; NR can simulate most promising sources - GW DA: LIGO has completed five science runs, and analyzed lots of data - extraction of h(t) from numerical evolution: psi_4 or Zerilli function - decompose h+ - ihx into spin-weighted spherical harmonics of weight -2; these must be provided by numerical groups as functions of time and incorporated into LAL searches - in practice: use metadata file to find files, rescale them for total mass, compute h(t) = F+ h+(t) + Fx hx(t), run injection - check sanity by injecting T1 3.5PN PN into white noise - then try injecting and recovering hybrid Ajith waveforms === Ruslan Vaulin - Estimating statistical significance of the candidate events in LSC compact binary coalescence search === === John Veitch - An Evidence Based Approach to Inspiral Followups === - compute probability that a candidate is really a gravitational wave - probability ratio (odds ratio) for signal vs. null hypothesis; does not need probability of the data - use Gaussian model of noise, integrate over signal parameters - code runs in 2hrs for 100s data - try with Gaussian noise only, model favors noise only - inject signal, Bayes factor increases with SNR - tried polluting Gaussian noise with time-domain Poisson components, noise model still significantly favored for noise only, but sensitivity to signal is reduced - how does technique behave with unmodeled glitches in noise? Try with nonphysical ringdowns... show robust behavior - ideal follow-up---conceptually straightforward, can be used for other signals than inspirals, too posters: Tagoshi on coherent-search strategies McKechan on higher harmonics -- check out van der Sluys on Bayesian inference for inspirals -- check out his errors Bose on coherent searches