High-energy emitting BL Lacs and high-energy neutrinos

Prospects for the direct association with IceCube and KM3NeT

¹ Dipartimento di Fisica, Università dell’Insubria – via Valleggio, 11 - 22100 Como, Italy
² INAF–Osservatorio Astronomico di Brera, via E. Bianchi 46, 23807 Merate, Italy
e-mail: Fabrizio.Tavecchio@brera.inaf.it
³ INAF–Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monte Porzio Catone, Italy
⁴ Department of Physics Optical Engineering, ORT Braude, PO Box 78, Carmiel, Israel

Received: 25 July 2016
Accepted: 25 September 2016

Abstract

Context. The origin of the high-energy flux of neutrinos detected by IceCube remains unknown. Recent works report evidence for a possible positional correlation between the reconstructed neutrino arrival directions and the positions in the sky of low-power, high-energy-emitting BL Lac objects (HBL).

Aims. Assuming that γ-ray-emitting HBL form the bulk of the sources of high-energy neutrinos above 100 TeV, we intend to calculate the number of events expected to be detected for each source by IceCube and KM3NeT.

Methods. Based on a simple theoretically-motivated framework inspired by the structured jet scenario for these sources, we postulate a direct proportionality between high-energy γ-ray and neutrino fluxes. We calculate the expected neutrino event rate for the HBL sources of the Second Fermi-LAT Catalog of High-Energy Sources (2FHL) for IceCube and the presently under-construction KM3NeT using declination-dependent and exposure-weighted effective areas.

Results. We provide a list of 2FHL HBL with the calculated number of events. For IceCube, the derived count rate for several sources is relatively high, of the order of ≲1 yr^-1, consistent with the recent findings of a possible positional correlation. For KM3NeT, the calculated rates are higher, with several sources with expected rates exceeding 1 yr^-1. This, coupled with the improved angular resolution, implies that the HBL origin can be effectively tested with few years of observation of KM3NeT (and IceCube Gen2, for which similar performances are foreseen) through the direct association of neutrinos and single HBL.

Conclusions. Our results show that if, as suggested by recent works, HBL represent a possible population of high-energy neutrino emitters, several single sources should be identified in a few years of exposure of KM3NeT, highlighting the importance of the improved angular resolution anticipated for KM3NeT and IceCube Gen2.