Multimessenger observations may hold the key to learn about the most energetic sources in the universe. The recent construction of new, large scale observatories opened new possibilities in testing cosmic processes with alternative probes, such as high energy neutrinos and gravitational waves.
Multimessenger observations may hold the key to learn about the most energetic sources in the universe. The recent construction of new, large scale observatories opened new possibilities in testing cosmic processes with alternative probes, such as high energy neutrinos and gravitational waves.
We propose to combine information from transient sources of electromagnetic signals (low and high energy photons) with neutrino observations to decipher a comprehensive picture of some of the most extreme cosmic processes. Transient sources will help in the identification of sources requiring the space and time coincidence of the observations.
In particular we will concentrate on the most promising photon emitter sources: transient Active Galactic Nuclei and sources of Gamma Ray Bursts. Electromagnetic information, including their spectral properties, will be acquired from public data-bases (like the ones provided by FERMI experiment), neutrino data will come from public IceCube data-base and by ANTARES data.
The joint detection of electromagnetic signals and neutrinos from these sources will probe the physics of the sources and will be a smoking gun of the presence of hadrons in these objects which is still an open question.
Conversely, the non-detection of neutrinos from these sources will be fundamental to constrain the hadronic content and gain information on the physics of these objects.
These analysis method, based on the reduction of the background thanks to the space-time coincident observation of different messengers coming from the same source, is at present the most promising procedure to search for high energy astrophysical sources.
At the highest energies, the picture of the Universe is remarkably incomplete, it is opaque to photons above a few 100 GeV. Cosmic rays are detected at ultra-high energies, but their arrival directions are scrambled by intergalactic magnetic fields and cannot provide information about the sites where they have been accelerated. Neutrinos will give us an unobstructed, direct view of the Universe, mainly on the regions where the extreme accelerations are possible.
Electromagnetic signals are at present the most important information we have about the location of astrophysical sources. Unfortunately, these information are not sufficient to shed light on the processes that originate the observed photon flux. Two possible scenarios can explain the amount and the energy spectrum of the observed gamma flux: in one case the shock wave originated by the source accelerate electrons, in the other case protons are accelerated. In the first case the high energy electrons, interacting with the electromagnetic radiation surrounding the source (synchrotron radiation) via Inverse Compton, originate high energy photons. In this case not only we don't expect to observe photons at energies exceeding few tents of TeV but, and this is relevant for our proposal, it's not expected to find neutrinos. In the second case, if in the region around the source are present hadrons, the acceleration will provide high energy protons. The interaction of these protons and the synchrotron radiation will produce neutral and charged pions, from these particles we do expect both photons and neutrinos. For this reason, the common observation of photons and neutrinos from the same source can help to understand the nature and the dynamics of the source.
Due to the expected very low flux of high energy astrophysical neutrinos the identification of common gamma-neutrino source would be very difficult. If we restrict our search to "transient sources", i.e. to sources of electromagnetic signals that show a strong variation (more than a factor 10) of the flux intensity, not only we can reduce the neutrino search time interval to "high intensity emission time" but we can also enhance the statistical significance of a possible coincidence in time and direction of photons and neutrinos.
We plan to identify in the FERMI data-base interesting "transient sources" of photons and we will evaluate, for them, the expected neutrino fluxes.
The results of this research will be published in journals that have a high impact factor and they will be presented at international conferences, workshops and seminars.