GWTC-1: A Gravitational-Wave Transient Catalog of Compact Binary Mergers Observed by LIGO and Virgo during the First and Second Observing Runs

We present the results from three gravitational-wave searches for coalescing compact binaries with component masses above 1 Ma™ during the first and second observing runs of the advanced gravitational-wave detector network. During the first observing run (O1), from September 12, 2015 to January 19, 2016, gravitational waves from three binary black hole mergers were detected. The second observing run (O2), which ran from November 30, 2016 to August 25, 2017, saw the first detection of gravitational waves from a binary neutron star inspiral, in addition to the observation of gravitational waves from a total of seven binary black hole mergers, four of which we report here for the first time: GW170729, GW170809, GW170818, and GW170823. For all significant gravitational-wave events, we provide estimates of the source properties. The detected binary black holes have total masses between 18.6-0.7+3.2 Mâ™ and 84.4-11.1+15.8 Mâ™ and range in distance between 320-110+120 and 2840-1360+1400 Mpc. No neutron star-black hole mergers were detected. In addition to highly significant gravitational-wave events, we also provide a list of marginal event candidates with an estimated false-alarm rate less than 1 per 30 days. From these results over the first two observing runs, which include approximately one gravitational-wave detection per 15 days of data searched, we infer merger rates at the 90% confidence intervals of 110-3840 Gpc-3 y-1 for binary neutron stars and 9.7-101 Gpc-3 y-1 for binary black holes assuming fixed population distributions and determine a neutron star-black hole merger rate 90% upper limit of 610 Gpc-3 y-1. © 2019 authors. Published by the American Physical Society

Laser frequency stabilization for the sub-SQL interferometer

A century after the existence of gravitational waves was predicted by Albert Einstein in his general theory of relativity, the first direct detection was made on September 14 in 2015. Continuous upgrades and improvements of the Advanced LIGO (aLIGO) gravitational wave observatories have increased their sensitivity and made this detection possible. In the final sensitivity configuration, the detectors are limited by quantum noise. Prototypes are required to carry out further developments to reduce the noise level below quantum noise. In order to reach and subsequently surpass the Standard Quantum Limit (SQL) of interferometry, the AEI 10m Prototype facility was developed at the Albert Einstein Institute (AEI) in Hanover. The achievement of extreme stability in frequency of the laser source for the sub-SQL interferometer is required. For this purpose, a 21 m long, fully suspended triangular ring cavity was established to provide a stable length reference on which the laser frequency is stabilized. To reduce the frequency noise of the free-running laser, the scope of this thesis was the assembly and commissioning of the frequency reference cavity. The initial design has been improved to suppress the noise sources affecting the cavity length. To ensure continuous stabilization of the system, an automatic alignment of the input beam to the cavity was developed and implemented. The cavity optics are suspended as triple pendulums for isolation from seismic noise. Around the pendulum resonance frequencies from 0.5 Hz to 10 Hz, the cavity optics are actively controlled by means of a feedback control loop. This has been improved by the use of new digital filters for a degree of freedom dependent damping and reduced the mirror motion at the fundamental longitudinal resonance frequency to 2x10^-2 μm/sqrt(Hz). A further suppression of cavity mirror motion was achieved by implementing a new concept for active cavity length stabilization. This technique uses the mode cleaner feedback signal to control the length of the frequency reference cavity below 2 Hz by acting on the longitudinal motion of curved cavity mirrors. This damping improvement reduced the mirror motion to 2x10^-3 μm/sqrt(Hz). The triple suspensions are commissioned and the stabilization of the mechanical resonances is successful. In addition, a new concept of low-frequency cavity length control has been implemented. The foundations for achieving the performance of laser frequency stabilization have been established to enable the operation of the sub-SQL interferometer