IOP Publishing, Journal of Cosmology and Astroparticle Physics, 11(2014), p. 017-017, 2014
DOI: 10.1088/1475-7516/2014/11/017
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Context. The jets of radio-loud Active Galactic Nuclei are among the most powerful particle accelerators in the Universe, and a plausible production site for high-energy cosmic rays. The detection of high-energy neutrinos from these sources would provide un- ambiguous evidence of a hadronic component in such jets. High-luminosity blazars, such as the flat-spectrum radio quasars (FSRQs), are promising candidates to search for such emission. Because of the low fluxes due to large redshift, these sources are however challenging for the current generation of neutrino telescopes such as ANTARES and IceCube. Aims. This paper proposes to exploit gravitational lensing effects to improve the sensitivity of neutrino telescopes to the intrinsic neutrino emission of distant blazars. Methods. This strategy is illustrated with a search for cosmic neutrinos in the direction of four distant and gravitationally lensed blazars, using data collected from 2007 to 2012 by ANTARES. The magnification factor is estimated for each system assuming a singular isothermal profile for the lens. The neutrino event selection and statistical analysis are identical to the already published ANTARES search for neutrino point sources, which included a few (non-lensed) FSRQs. Based on ANTARES data, we derive upper limits on the intrinsic luminosity of the selected lensed sources. We obtain the strongest constraint from the lensed system B0218+357, providing a limit on the total neutrino luminosity of this FSRQ of 1.08 × 10^(46) ergs−1. This limit is about one order of magnitude lower than those obtained in the ANTARES standard point source search with non-lensed FSRQs, demonstrating the utility of the method.