Neutrino production in Population III microquasars

Abstract

Microquasars (MQs) are binary systems composed by a star feeding mass to a compact object through an accretion disk. The compact object, usually a black hole, launches oppositely directed jets which are typically observed in our galaxy through their broadband electromagnetic emission. These jets are considered potential galactic neutrino sources. MQs can also have been formed by the first generations of stars in the universe, i.e., Population III (Pop III) stars, which are considered essential contributors to the ionization processes that took place during the period of 'cosmic reionization'. In the present work, we develop a model that accounts for the main particle processes occurring within Pop III MQ jets, with the aim to obtain the diffuse neutrino flux at the Earth [...] We find that, for a range of parameters suitable for Pop III MQ jets, the most relevant site for neutrino production in the jets is the base of the inner conical jet. Additionally, if protons accelerated at the forward shock formed at terminal jet region can escape from the outer shell, they would produce further neutrinos via $p{\gamma}$ interactions with the cosmic microwave background (CMB). The latter contribution to the diffuse neutrino flux turns out to be dominant in the range $10^7 {\rm GeV} \lesssim E_{\nu} \lesssim 10^9 {\rm GeV}$, while the neutrinos produced in the inner jet could only account for a small fraction of the IceCube flux for $E_{\nu}\sim 10^5$ GeV. The co-produced multiwavelength photon background is also computed and it is checked to be in agreement with observations.