University of Wisconsin-Madison

ANTARES and IceCube, a first joint search for neutrino sources launches a future of further collaboration

IceCube is not alone in the search for the sources of astrophysical neutrinos and cosmic rays. Multimessenger studies in collaboration with other observatories such as LIGO and Virgo or optical and X-ray telescopes have already brought interesting results. Joining forces with other neutrino telescopes is another strategy to consider.

New results submitted today to the Astrophysical Journal are the outcome of a combined search for neutrino point sources performed by the ANTARES and IceCube collaborations. No source has been identified, but the combined search improves the sensitivity to point sources by up to a factor of two, which delivers more stringent upper limits on the flux for the candidate sources considered in this analysis.

90% CL sensitivities and limits for the neutrino emission from point sources  as  a  function of source declination in the sky. Green points indicate the actual limits on the  candidate sources. The green line indicates the sensitivity of the combined search.  Curves/points respectively indicate the published sensitivities/limits for the IceCube (blue) and ANTARES (red) analyses, respectively. Image: ANTARES and IceCube Collaborations
90% CL sensitivities and limits for the neutrino emission from point sources as a function of source declination in the sky. Green points indicate the actual limits on the candidate sources. The green line indicates the sensitivity of the combined search. Curves/points respectively indicate the published sensitivities/limits for the IceCube (blue) and ANTARES (red) analyses, respectively. Image: ANTARES and IceCube Collaborations

ANTARES is a Cherenkov neutrino detector, similar in principle to IceCube but deployed in the deep sea rather than glacial ice. It is smaller than IceCube, but its location in the Mediterranean Sea allows it to use the Earth as a filter when viewing the southern sky, giving it more sensitivity to neutrinos with energies below 100 TeV in this part of the sky, a region that includes many galactic sources.

Using IceCube data from 2008-2011 combined with ANTARES data from 2007-2012, researchers have looked for neutrino point sources using muon track events. The search for any excess of events in the full southern sky found the most significant cluster at equatorial coordinates α=332.8° and δ=-46.1°, with a final significance of 0.7 sigma. A second search for 40 candidate sources was also performed and, again, resulted in no significant excess.

An important result of this study is that the sensitivity of the combined ANTARES-IceCube southern sky search for a region centered at the declination of the Galactic center improves by a factor of 2 compared to the sensitivity of each experiment separately.

Joint searches by these two neutrino detectors will continue and are expected to provide the best point-source sensitivity in many regions of the southern sky, including those where Galactic sources are expected to be found. Stay tuned!

+ Info: “First combined search for neutrino point-sources in the Southern Hemisphere with the ANTARES and IceCube neutrino telescopes,” ANTARES and IceCube Collaborations: S. Adrián-Martínez et al. Astrophysical Journal 823 (2016) 65, iopscience.iop.org arxiv.org/abs/1511.02149