Multimessenger astronomy with the Einstein Telescope

Gravitational waves (GWs) are expected to play a crucial role in the development of multimessenger astrophysics. The combination of GW observations with other astrophysical triggers, such as from gamma-ray and X-ray satellites, optical/radio telescopes, and neutrino detectors allows us to decipher science that would otherwise be inaccessible. In this paper, we provide a broad review from the multimessenger perspective of the science reach offered by the third generation interferometric GW detectors and by the Einstein Telescope (ET) in particular. We focus on cosmic transients, and base our estimates on the results obtained by ET's predecessors GEO, LIGO, and Virgo.Comment: 26 pages. 3 figures. Special issue of GRG on the Einstein Telescope. Minor corrections include

Towards improving the prospects for coordinated gravitational-wave and electromagnetic observations

We discuss two approaches to searches for gravitational-wave (GW) and electromagnetic (EM) counterparts of binary neutron star mergers. The first approach relies on triggering archival searches of GW detector data based on detections of EM transients. We introduce a quantitative approach to evaluate the improvement to GW detector reach due to the extra information gained from the EM transient and the increased confidence in the presence of a signal from a binary merger. We also advocate utilizing other transients in addition to short gamma ray bursts. The second approach involves following up GW candidates with targeted EM observations. We argue for the use of slower but optimal parameter-estimation techniques to localize the source on the sky, and for a more sophisticated use of astrophysical prior information, including galaxy catalogs, to find preferred followup locations.Comment: Full text for proceedings of New Horizons in Time-domain Astronomy, IAU Symposium 285 [published proceedings will be abbreviated

Pulsar timing arrays and the challenge of massive black hole binary astrophysics

Pulsar timing arrays (PTAs) are designed to detect gravitational waves (GWs) at nHz frequencies. The expected dominant signal is given by the superposition of all waves emitted by the cosmological population of supermassive black hole (SMBH) binaries. Such superposition creates an incoherent stochastic background, on top of which particularly bright or nearby sources might be individually resolved. In this contribution I describe the properties of the expected GW signal, highlighting its dependence on the overall binary population, the relation between SMBHs and their hosts, and their coupling with the stellar and gaseous environment. I describe the status of current PTA efforts, and prospect of future detection and SMBH binary astrophysics.Comment: 18 pages, 4 figures. To appear in the Proceedings of the 2014 Sant Cugat Forum on Astrophysics. Astrophysics and Space Science Proceedings, ed. C.Sopuerta (Berlin: Springer-Verlag

The Dawn of Multi-Messenger Astronomy

The recent discoveries of high-energy astrophysical neutrinos and gravitational waves have opened new windows of exploration to the Universe. Combining neutrino observations with measurements of electromagnetic radiation and cosmic rays promises to unveil the sources responsible for the neutrino emission and to help solve long-standing problems in astrophysics such as the origin of cosmic rays. Neutrino observations may also help localize gravitational-wave sources, and enable the study of their astrophysical progenitors. In this work we review the current status and future plans for multi-messenger searches of neutrino sources.Comment: To appear in "Neutrino Astronomy- Current status, future prospects", Eds. T. Gaisser & A. Karle (World Scientific

Multimessenger astronomy with pulsar timing and X-ray observations of massive black hole binaries

We demonstrate that very massive (>10^8\msun), cosmologically nearby (z<1) black hole binaries (MBHBs), which are primary targets for ongoing and upcoming pulsar timing arrays (PTAs), are particularly appealing multimessenger carriers. According to current models for massive black hole formation and evolution, the planned Square Kilometer Array (SKA) will collect gravitational wave signals from thousands of such massive systems, being able to individually resolve and locate in the sky several of them (maybe up to a hundred). By employing a standard model for the evolution of MBHBs in circumbinary discs, with the aid of dedicated numerical simulations, we characterize the gas-binary interplay, identifying possible electromagnetic signatures of the PTA sources. We concentrate our investigation on two particularly promising scenarios in the high energy domain, namely, the detection of X-ray periodic variability and of double broad K\alpha iron lines. Up to several hundreds of periodic X-ray sources with a flux >10^-13 erg s^-1 cm^-2 will be in the reach of upcoming X-ray observatories. Double relativistic K\alpha lines may be observable in a handful of low redshift (z<0.3) sources by proposed deep X-ray probes, such as Athena. (Abridged)Comment: 19 pages, 11 figures, submitted to MNRAS, minor revision of the reference lis

Results from the ANTARES Neutrino Telescope

A primary goal of a deep-sea neutrino telescopes as ANTARES is the search for astrophysical neutrinos in the TeV-PeV range. ANTARES is today the largest neutrino telescope in the Northern hemisphere. After the discovery of a cosmic neutrino diffuse flux by the IceCube, the understanding of its origin has become a key mission in high-energy astrophysics. ANTARES makes a valuable contribution for sources located in the Southern sky thanks to its excellent angular resolution in both the muon channel and the cascade channel (induced by all neutrino flavors). Assuming various spectral indexes for the energy spectrum of neutrino emitters, the Southern sky and in particular central regions of our Galaxy are studied searching for point-like objects and for extended regions of emission. In parallel, by adopting a multimessenger approach, based on time and/or space coincidences with other cosmic probes, the sensitivity of such searches can be considerably augmented. ANTARES has participated to a high-energy neutrino follow-up of the gravitational wave signal GW150914, providing the first constraint on high-energy neutrino emission from a binary black hole coalescence. ANTARES has also performed indirect searches for Dark Matter, yielding limits for the spin-dependent WIMP-nucleon cross-section that improve upon those of current direct-detection experiments.Comment: Proceedings of the CRIS2016 (10th Cosmic Ray International Seminar) - Ischia (NA) Italy, July 4-8, 201