Session L14: Multimessenger Detection Strategies

Searching for Electromagnetic Counterparts in DESGW Follow-up Data of Binary Black Hole Events

The number of binary black hole (BBH) mergers detected by the LIGO/Virgo Collaboration currently exceeds the number of binary neutron star mergers by a factor 10 and will only increase with upgrades to current gravitational wave (GW) detectors and the addition of new GW instruments in the near future. Mergers that yield both GW and electromagnetic (EM) signals are especially valuable to cosmology and can provide a direct measurement of the Hubble Constant. BBH mergers, which make up the greatest number of detected GW, however, only have EM counterparts under complex circumstances. In this talk, we will discuss the conditions in which BBH mergers would generate EM counterparts and place these models in context with the Dark Energy Survey's optical follow-up campaign of GW events. Our result, combining data from all three observing campaigns, is the most comprehensive search for EM counterparts of BBH mergers to date.   

Multiwavelength Follow-up Observations of Astrophysical Neutrino Events

On September 22, 2017, the IceCube Neutrino Observatory detected a high-energy neutrino of potential astrophysical origin which was found by follow-up electromagnetic observations to spatially and temporally coincide with the flaring state of a known blazar, TXS 0506+056. Since then, several additional neutrino events have been found in spatial correlation with known high-energy sources. Multiwavelength follow-up observations of astrophysical neutrino events such as these, and the continued monitoring of previously-identified sources such as TXS 0506+056 are imperative in finding sources of the diffuse neutrino flux detected by IceCube as well as the origins of high-energy cosmic rays. Here, we present results from multiwavelength follow-up observations of astrophysical neutrino candidate events with potential gamma-ray counterparts, including observations at X-ray and gamma-ray energies performed by the Neil Gehrels Swift Observatory, NuSTAR, and the Fermi Gamma-ray Space Telescope.   

Over the threshold: Application for Multimessenger Searches using High-Energy Neutrinos and Gravitational-Wave Candidates Below the Detection Limit

Gravitational-wave (GW) emission from cosmic sources can be accompanied by other messengers across the electromagnetic spectrum, as well as by particles such as high-energy neutrinos (HENs). Joint gravitational-wave -- high-energy neutrino sources can be discovered by searching subthreshold events in both data streams as time and spatially coincident GW+HEN candidates may rise above the detection threshold. Here we present the application of the Low-Latency Algorithm for Multimessenger Astrophysics (LLAMA) pipeline for joint searches for common sources of gravitational-waves and high-energy neutrinos using subthreshold data streams.   

Multi-resolution HEALPix maps tools for multi-messenger astronomy

HEALPix -- the Hierarchical Equal Area isoLatitude Pixelization – is a standard for tessellating the sphere originally developed to improve the analysis of full-sky data sets. Thanks to its convenient geometric and algebraic properties it has now been adopted by multiple astronomical fields for various purposes, including the distribution of sky-localization probability maps by LIGO, Virgo and Kagra (LVK) and Fermi-GBM. As part of the Time-domain Astronomy Coordination Hub (TACH), in this contribution we present a series of tools that support the usage of multi-resolution maps and enable the use HEALPix to distribute sky-localization information and other astronomical data even by instruments with milliarcsecond resolution. This makes HEALPix a suitable candidate for a common format that can facilitate multi-messenger and multi-wavelength coordination and analysis. The tools include mhealpy, a general-purpose object-oriented Python library that provides an unified interface for single-resolution and multi-resolution HEALPix maps;  a derived package to perform common operations needed to create and analyze sky localization probability maps; and healpix-alchemy, a package to add fast multi-resolution image arithmetic and set operations on sky regions to any PostgreSQL 14 database.   

The NuEM Multimessenger Channel with AMON

The Neutrino-Electromagnetic (NuEM) channel from the Astrophysical Multimessenger Observatory Network(AMON), has been developed as a real-time alert system. The AMON server performs coincidence analyses using gamma-ray and neutrino data from different detectors.. AMON takes advantage of sub-threshold events, i.e. events that by themselves are not significant in the individual detectors. However, signal events can be recovered when looking at the datasets together. The main purpose of the NuEM channel is to search for neutrino sources. We will describe the analyses that make-up this channel and some od the recent results.   

Probing the Multimessenger Nature of AGNs with AMEGO-X

Active galactic nuclei (AGNs) harbor intense environments that are ripe for efficient particle acceleration; however, whether they accelerate cosmic rays and produce neutrinos remains a long-standing mystery. Recently, multimessenger observations in gamma rays and neutrinos culminated in the 2017 joint detection of a flare from blazar TXS 0506+056. Additionally, the IceCube Observatory has reported observations of neutrino excesses associated with TXS 0506+056 (occurring within a 5-month period in 2014-2015) and with the radio-quiet AGN NGC 1068. While still tentative (<~ 3 sigma), these observations have provided the strongest evidence to date of a possible connection between AGNs and neutrinos. Further confirmation of this connection will require more joint observations with gamma rays, for which the medium-energy band is the best indicator as the radiation fields required for efficient neutrino production make the source opaque to higher-energy gamma rays. The All-sky Medium Energy Gamma-ray Observatory eXplorer (AMEGO-X) is a Compton-pair telescope that will feature unprecedented sensitivity in the medium-energy gamma-ray band (100 keV — >1 GeV), excellent localization capability, and groundbreaking polarization sensitivity between 100 keV and 1 MeV. AMEGO-X observations of AGNs will be crucial to probing their multimessenger nature.   

Observing neutron star mergers and the shock breakout of supernovae with SIBEX

Time-domain astrophysical objects such as supernovae and gamma-ray bursts are central to compact object formation, heavy element creation, and multi-messenger astronomy. Because of their link to many areas of astrophysics, observational data of supernovae and gamma-ray bursts have grown by leaps and bounds over the last decade, including UV supernova data from the NASA Neil Gehrels Swift Observatory and the first gravitational and electromagnetic wave detection of a neutron star merger. Unfortunately, most of these observations occur after the initial explosion when interactions with the surrounding environment shrouds our interpretations of the observations. The most penetrating and critical observations of these transients and their progenitors require a prompt observation in the X-ray and UV when the first photons appear.

 

The Shock Interaction and Breakout EXplorer (SIBEX) is a proposed MIDEX mission designed to obtain the earliest supernovae and nutetron star merger observations. SIBEX accomplishes this by monitoring large areas of the sky to detect the earliest supernova and neutron star merger photons by using its very wide field-of-view soft X-ray telescopes (XRF) to localize outbursts. Immediately after a localization is provided by XRF, a rapidly slewing spacecraft autonomously positions a co-located narrow-field UV telescope (SUSI) on the provided position. A refined position is provided by SUSI from which the spacecraft repositions SUSI in order to place its spectroscopic slit on the source in order to probe the outburst environment. No other past, present, or planned observatories have the combined SIBEX X-ray and UV capabilities for exploring ~50 shock breakouts of supernovae and ~25 neutron star mergers in a three year mission.