First gravitational-wave search for intermediate-mass black hole mergers with higher order harmonics

TL;DR

This paper introduces a new gravitational-wave search method that includes higher-order modes to better detect intermediate-mass black hole mergers, significantly improving sensitivity for edge-on sources with asymmetric masses.

Contribution

The paper presents a novel search technique incorporating higher-order modes, adapted discriminators, and ranking statistics, enhancing detection capabilities for specific black hole merger signals.

Findings

Sensitivity gain of up to 450% for targeted signals

No new candidates found beyond previous reports

Sets groundwork for future higher-mode gravitational-wave searches

Abstract

Current matched-filter searches for gravitational waves from binary black-hole mergers compare the calibrated detector data to waveform templates that omit the higher-order mode content of the signals predicted by General Relativity. However, higher-order emission modes become important for highly inclined asymmetric sources with masses above $\simeq 100 M_\odot$, causing current searches to be ill-suited at detecting them. We present a new gravitational-wave search that implements templates including higher-order modes, adapted signal-glitch discriminators, and trigger-ranking statistics to specifically target signals displaying strong higher modes, corresponding to nearly edge-on sources with total redshifted masses in the intermediate-mass black-hole range $M_T(1+z) \in (100,500) M_\odot$ and mass-ratios $q\in(1,10)$. Our search shows a volumetric sensitivity gain of up to $450\%$ to these signals compared to existing searches omitting higher-order modes. We deploy our search on public data from the third observing run of Advanced LIGO. While we find no statistically significant candidates beyond those already reported elsewhere, our search sets the stage to search for higher-mode rich signals in future observing runs. The efficient detection of such signals is crucial to performing detailed tests of General Relativity, observing strong-field phenomena, and maximizing the chances of observing the yet uncharted realm of intermediate-mass black hole binaries.