A Comparison of Burst Gravitational Wave Detection Algorithms for LIGO Amber L. Stuver Center for Gravitational Wave Physics Penn State University

15 Dec 2005A. Stuver - CGWP, Penn State2 Overview Burst Data Analysis Algorithms Strongest False Alarm Events –Do the algorithms see the data in the same way? Simulated Signal Performance –How do the algorithms differ with different signals? Population Performance –What is the relative performance of each algorithm given a population? Conclusions

15 Dec 2005A. Stuver - CGWP, Penn State3 Data Analysis Algorithms (ETG) BlockNormal –searches data for statistical “change points” and divides the data into blocks of data with consistent mean and variance. A block is reported if it differs by a significant amount from the statistics of the larger data set. SLOPE –finds the best-fit straight line through intervals of the timeseries and if the slope is sufficiently improbable, the interval is reported Q Pipeline –a multi-resolution time-frequency search for excess power. The data are projected onto bases that are logarithmically spaced in frequency and Q, and linearly in time and the most significant set of non- overlapping tiles are reported

15 Dec 2005A. Stuver - CGWP, Penn State4 Strongest False Alarm Events If each ETG “looks” at the data in a fundamentally equivalent way, then they should identify the same strongest false events. Strongest defined as the largest magnitude of whatever quantity each ETG identifies Data set is a subset of LIGO science data (S3) without any signal injections and assumed to be noise only

15 Dec 2005A. Stuver - CGWP, Penn State5 View of All Strongest False Events Locations of the 10 strongest BlockNormal, SLOPE and Q Pipeline events from a contiguous stretch of 600 seconds of data. The most significant events identified by the three ETG’s are different. Upon inspection, the events themselves do not appear, by eye, to have obvious differences.

15 Dec 2005A. Stuver - CGWP, Penn State6 Events All ETGs “Saw” Of the events that all 3 ETGs identify, do they rank the strength in the same way? If the ETGs are equivalent on this level, a scatter plot of the rank of an event in one ETG to the rank in other will cluster along the diagonal… –They don’t.

15 Dec 2005A. Stuver - CGWP, Penn State7 SLOPE & BlockNormal SLOPE BlockNormal

15 Dec 2005A. Stuver - CGWP, Penn State8 Q Pipeline & SLOPE Q Pipeline SLOPE

15 Dec 2005A. Stuver - CGWP, Penn State9 Q Pipeline & BlockNormal Q Pipeline BlockNormal

15 Dec 2005A. Stuver - CGWP, Penn State10 Simulated Signal Performance ETGs are not fundamentally equivalent and signal properties that ETG was sensitive to was not initially obvious What, then, are the signal properties that each ETG favor? To determine specific signal sensitivities: –Simulate signals of different lengths and amplitudes and inject into a white noise background (zero mean and unit variance)

15 Dec 2005A. Stuver - CGWP, Penn State11 Amplitude for 50% Detection BlockNormal Black Hole Ringdown White Noise & Sine- Gaussians

15 Dec 2005A. Stuver - CGWP, Penn State12 Amplitude for 50% Detection SLOPE 64 Hz 16 Hz White Noise

15 Dec 2005A. Stuver - CGWP, Penn State13 Population Performance Convolve the detection efficiency surface with a population The integral of this gives a measure of an ETG’s performance WRT a population

15 Dec 2005A. Stuver - CGWP, Penn State14 Measured Population Performances BlockNormal has fairly consistent performance over different signal types. While SLOPE’s performance can be higher, it is not as reliable. * Population values are normalized to this Disk (~ A -3 )Isotropic (~ A -4 ) BlockNormalSLOPEBlockNormalSLOPE White Noise * * SG16 Hz Hz BH 16 Hz Hz

15 Dec 2005A. Stuver - CGWP, Penn State15 Conclusions BlockNormal, SLOPE and Q Pipeline do not detect the same strongest events.  Among the events that are coincident, the significance of the event, as identified by the ETG’s, is uncorrelated. There are signal properties that distinguish the preferences of each ETG.  SLOPE has a strong frequency dependence while BlockNormal favors impulsive events. The overall shape of the detection fraction surface is meaningful for describing an ETG’s performance.  BlockNormal has a consistent performance over different signal types while SLOPE varies depending on the signal frequency.