Academic Papers
===============

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

.. _llama-o2-paper:

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

   :download:`PDF download <../papers/1901.05486.pdf>`

*Stefan Countryman, Azadeh Keivani, Imre Bartos, Zsuzsa Marka, Thomas
Kintscher, Rainer Corley, Erik Blaufuss, Chad Finley, Szabolcs Marka*
(`arXiv <https://arxiv.org/abs/1901.05486>`__,
`NASA ADS <https://ui.adsabs.harvard.edu/#abs/arXiv:1901.05486>`__)

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.

.. _llama-bayesian-paper:

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

   :download:`PDF download <../papers/1810.11467.pdf>`

*Imre Bartos, Doga Veske, Azadeh Keivani, Zsuzsa Marka, Stefan Countryman, Erik
Blaufuss, Chad Finley, Szabolcs Marka*
(`arXiv <https://arxiv.org/abs/1810.11467>`__,
`NASA ADS <https://ui.adsabs.harvard.edu/#abs/arXiv:1810.11467>`__)

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.