Session B13: Multimessenger Astronomy I

The Astrophysical Multimessenger Observatory Network

The Astrophysical Multimessenger Observatory Network (AMON) aims to connect the world's leading high-energy and multimessenger observatories. AMON's objective are to evoke the discovery of new multimessenger phenomena, exploit these phenomena as tools for fundamental physics and astrophysics, and explore archival datasets in search of multimessenger activity. Currently, AMON is distributing low-latency multimessenger alerts from the Neutrino-Electromagnetic (NuEM) channel, and triggering real-time preservation and analysis of data from NASA's Swift satellite based on LIGO+Virgo+Kagra gravitational-wave alerts. Looking ahead, AMON will continue providing useful real-time analyses of a wide variety of high-energy and multimessenger data streams, while upgrading its systems to cloud-based and SCiMMA-standard cyberinfrastructure, and strengthening its ties with the theoretical and time domain astrophysics communities.   

LIGO-Virgo-KAGRA data products in the fourth observing run

Kilonova observations are crucial for our understanding of the neutron star equation of state and r-process nucleosynthesis. In compact binary mergers with at least one neutron star, the equation of state influences how much matter is ejected from the merger, and this neutron-rich ejecta is expected to be a site of r-process nucleosynthesis. Kilonova are faint and short lived, however, and finding them is no easy task. Electromagnetic follow-up of gravitational wave observations of mergers, like the combined detection of GW170817 and AT 2017gfo, give us our best chance at detecting kilonovae in the near future. As LIGO's fourth observing run approaches, we present the techniques and data products that will be used to assist follow-up of electromagnetic counterparts to gravitational wave detections, and the ongoing validation of these products in real-time replay through the Mock Data Challenge. We cover both public data products, as well as those in development, such as kilonova light curve predictions.   

LIGO-Virgo-KAGRA real-time discovery alerts in the fourth observing run

More than half a decade has passed since the real-time coincident detection of gravitational waves (GWs) and electromagnetic (EM) radiation from the binary neutron star merger, GW170817. During the 2019-2020 LIGO-Virgo third observing run (O3), discovery alerts for several tens of candidates were sent publicly to the EM and neutrino communities for follow-up. The events spanned greater distances and sky-localizations ranging from tens to thousands of square degrees. The fourth observing run (O4), which is scheduled to begin later in 2023, is expected to observe up to twice as many events as O3. Several of these are expected to be promising candidates for multi-messenger astronomy, but it also increases the risk and burden of follow-up. LIGO-Virgo-KAGRA has performed several upgrades to the alert infrastructure to assist the external community. In this talk, I will describe the public alert campaign of the LIGO-Virgo-KAGRA collaboration for O4.   

Machine learning based source properties inference for fourth observing run of LIGO-Virgo-KAGRA

Prompt identification of gravitational wave (GW) sources capable of producing electromagnetic emissions is essential to extracting the maximum amount of physical information, as it allows astronomers to launch observing campaigns within minutes of the GW triggers. Timely sky localization of electromagnetically bright events, such as GW170817, makes possible the identification of the progenitor's host galaxy, the study of relativistic jet and non-relativistic ejecta formation, and detailed analyses of the post-merger phase. Astronomers are also interested in following up GW sources whose component masses lie in the "lower mass-gap" region between neutron stars and black holes (3-5 solar masses). In this work, we present a machine learning-based suite of algorithms for the inference of GW source properties that provide (1) the probability that at least one of the compact objects in the source binary progenitor has a mass consistent with the mass of a neutron star, (2) the probability that the merger ejected a nonzero mass outside the final remnant compact object, and (3) the probability that either of the component masses lie in the lower mass-gap region with high confidence and within seconds of a GW trigger. The algorithms provide these quantities within seconds and with an accuracy above 90%.   

Searching for Gravitational-Wave Counterparts using the Transiting Exoplanet Survey Satellite

In 2017, the LIGO and Virgo gravitational wave (GW) detectors, in conjunction with electromagnetic (EM) astronomers, observed the first GW multi-messenger astrophysical event, the binary neutron star (BNS) merger GW170817. This marked the beginning of a new era in multi-messenger astrophysics. To discover further GW multi-messenger events, we explore the synergies between the Transiting Exoplanet Survey Satellite (TESS) and GW observations triggered by the LIGO-Virgo-KAGRA Collaboration (LVK) detector network. TESS's extremely wide field of view of ∼2300 square degrees means that it could overlap with large swaths of GW localizations, which can often span hundreds of square degrees or more. In this work, we use a recently developed transient detection pipeline to search TESS data collected during the LVK's third observing run, O3, for any EM counterparts. We find no obvious counterparts brighter than about 17th magnitude in the TESS bandpass. Additionally, we present end-to-end simulations of BNS mergers, including their detection in GWs and simulations of light curves, to identify TESS's kilonova discovery potential for the LVK's next observing run (O4). In the most optimistic case, TESS will observe one GW-found BNS merger counterparts per year. However, TESS may also find up to five kilonovae which did not trigger the LVK network, emphasizing that EM-triggered GW searches may play a key role in future kilonova detections. We also discuss how TESS can help place limits on EM emission from binary black hole mergers, and rapidly exclude large sky areas for poorly localized GW events.   

IceCube search for neutrino-induced muons from gravitational wave sources

IceCube has searched for high-energy neutrinos associated with gravitational wave sources during LIGO/Virgo/KAGRA runs O1, O2, and O3. The analyses have occurred both in real time, reporting results typically within an hour of gravitational wave arrival at Earth, and on refined archival catalogs of gravitational wave events. IceCube localizes the neutrinos that produce muons to a sky area several hundred times smaller than typical gravitational wave localizations. Because of this, reporting results in real time can enable other telescopes to search a much smaller area for counterparts. We report results from searches through O3 as well as the status of real-time analysis during run O4.   

Timing coincidence search for supernovae neutrinos with optical transient surveys

Neutrinos allow us to peer into the inner workings of stars during core collapse, teaching us about the different stages and processes occurring. Currently, there has only been a single observed event that is a source of supernova neutrinos, SN1987A. Since then, most studies on supernova neutrinos have looked at different distance regimes, Galactic/local supernovae and the diffuse supernova neutrino background. We propose an intermediate distance regime in which there exists two separate approaches for detecting core-collapse supernova neutrinos at next generation detectors like Hyper-Kamiokande. The first approach relies on a close supernova that results in at least one measurable neutrino event. Transient surveys that focus on nearby galaxies, such as DLT40, will be able to provide the needed information regarding the timing of transience. The second approach relies on stacking core-collapse supernovae such that their summed events yield a detectable amount of neutrinos. Large transient surveys such as the upcoming LSST will be able to observe large amounts of supernovae over its 10 year lifetime. In both of these approaches, it is vitally important for the surveys to be able to pinpoint the time of core collapse to within the timescales of hours for confident neutrino detections.   

Neutrino Target-of-Opportunity Observations with EUSO-SPB2

Cosmic-ray accelerators capable of reaching ultra-high energies are expected to also produce very-high energy neutrinos via hadronic interactions within the source or its surrounding environment. Many of the candidate astrophysical source classes are either explicitly transient or exhibit flaring activity. Leveraging the Earth as a neutrino converter, suborbital and space-based optical Cherenkov detectors will be able to detect upward-moving extensive air showers induced by decay tau-leptons generated from cosmic tau neutrinos with energies ~ 10 PeV and above, reaching sensitivities at the level of modeled neutrino fluences for nearby astrophysical transients. We discuss the prospects of detecting tau neutrino events from astrophysical transients with the NASA super-pressure balloon mission EUSO-SPB2 as well as our preparations for neutrino Target-of-Opportunity observations during its upcoming flight in Spring 2023.