Academic Papers

This page contains links to relevant academic papers describing LLAMA and other related efforts and science.

Low-Latency Algorithm for Multi-messenger Astrophysics (LLAMA) with Gravitational-Wave and High-Energy Neutrino Candidates

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Stefan Countryman, Azadeh Keivani, Imre Bartos, Zsuzsa Marka, Thomas Kintscher, Rainer Corley, Erik Blaufuss, Chad Finley, Szabolcs Marka (arXiv, NASA ADS)

We describe in detail the online data analysis pipeline that was used in the multi-messenger search for common sources of gravitational waves (GWs) and high-energy neutrinos (HENs) during the second observing period (O2) of Advanced LIGO and Advanced Virgo. Beyond providing added scientific insight into source events, low-latency coincident HENs can offer better localization than GWs alone, allowing for faster electromagnetic follow-up. Transitioning GW+HEN analyses to low-latency, automated pipelines is therefore mission-critical for future multi-messenger efforts. The O2 Low-Latency Algorithm for Multi-messenger Astrophysics (LLAMA) also served as a proof-of-concept for future online GW+HEN searches and led to a codebase that can handle other messengers as well. During O2, the pipeline was used to take LIGO/Virgo GW candidates as triggers and search in realtime for temporally coincident HEN candidates provided by the IceCube Collaboration that fell within the 90% credible region of the reconstructed GW skymaps. The algorithm used NASA’s Gamma-ray Coordinates Network to report coincident alerts to LIGO/Virgo’s electromagnetic follow-up partners.

Bayesian Multi-Messenger Search Method for Common Sources of Gravitational Waves and High-Energy Neutrinos

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Imre Bartos, Doga Veske, Azadeh Keivani, Zsuzsa Marka, Stefan Countryman, Erik Blaufuss, Chad Finley, Szabolcs Marka (arXiv, NASA ADS)

Multi-messenger astrophysics is undergoing a transition towards low-latency searches based on signals that could not individually be established as discoveries. The rapid identification of signals is important in order to initiate timely follow-up observations of transient emission that is only detectable for short time periods. Joint searches for gravitational waves and high-energy neutrinos represent a prime motivation for this strategy. Both gravitational waves and high-energy neutrinos are typically emitted over a short time frame of seconds to minutes during the formation or evolution of compact objects. In addition, detectors searching for both messengers observe the whole sky continuously, making observational information on potential transient sources rapidly available to guide follow-up electromagnetic surveys. The direction of high-energy neutrinos can be reconstructed to sub-degree precision, making a joint detection much better localized than a typical gravitational wave signal. Here we present a search strategy for joint gravitational wave and high-energy neutrino events that allows the incorporation of astrophysical priors and detector characteristics following a Bayesian approach. We aim to determine whether a multi-messenger correlated signal is a real event, a chance coincidence of two background events or the chance coincidence of an astrophysical signal and a background event. We use an astrophysical prior that is model agnostic and takes into account mostly geometric factors. Our detector characterization in the search is mainly empirical, enabling detailed realistic accounting for the sensitivity of the detector that can depend on the source properties. By this means, we will calculate the false alarm rate for each multi-messenger event which is required for initiating electromagnetic follow-up campaigns.