Bayesian constraints on the astrophysical neutrino source population from IceCube data

Abstract

We present constraints on an astrophysical population of neutrino sources imposed by recent data from the IceCube neutrino observatory. By using the IceCube point source search method to model the detection of sources, our detection criterion is more sensitive than using the observation of high-energy neutrino multiplets for source identification. We frame the problem as a Bayesian hierarchical model to connect the high-level population parameters to the IceCube data, allowing us to consistently account for all relevant sources of uncertainty in our model assumptions. Our results show that sources with a local density of n 0 ≳ 10 −7 Mpc −3 and luminosity L ≲ 10 43 erg s −1 are the most likely candidates, but that populations of rare sources with n 0 ≃ 10 −9 Mpc −3 and L ≃ 10 45 erg s −1 can still be consistent with the IceCube observations. We demonstrate that these conclusions are strongly dependent on the source evolution considered, for which we consider a wide range of models. In doing so, we present realistic, modelindependent constraints on the population parameters that reflect our current state of knowledge from astrophysical neutrino observations. We also use our framework to investigate constraints in the case of possible source detections and future instrument upgrades. Our approach is flexible and can be used to model specific source cases and extended to include multimessenger information.

Assessing coincident neutrino detections using population models

“…Alternatively, if we only consider contributions from blazar flares, we expect Y νγ ∼ 10 −3 -10 −1 to be consistent with one neutrino-blazar flare coincidence in 10 years of observations. However, in Capel et al (2020), we demonstrated that rare and bright blazars capable of fulfilling these scenarios are also strongly constrained by the non-observation of point sources, further complicating the physical picture (consistent with Yuan et al 2019).…”

“…All sources of interest belong to some class of sources with similar properties and so the two are inextricably linked. General constraints on the density and effective luminosity of an unknown source population can be derived by requiring it to be able to produce the total astrophysical neutrino flux seen by IceCube, without containing individual sources that would have been detected by previous point source searches of the integrated data (Murase & Waxman 2016;Capel et al 2020). However, to study these proposed associations in a meaningful way, a more specific modelling of the population and its multimessenger connections is necessary.…”

Dark matter neutrino scattering in the galactic centre with IceCube

“…It is predicted that astrophysical neutrinos are produced in the highest energy extragalactic sources such as the super-massive black holes at the centre of active galactic nuclei [46,47], the collapse of massive stars in gamma ray bursts [48,49], or in star burst galaxies [50]. Although some potential points sources have been identified and there is growing evidence for the blazar connection [51,52], the exact nature of astrophysical neutrino sources remain uncertain [53][54][55][56][57][58][59][60][61][62].…”

Evaluating cosmic coincidences in the context of astrophysical source populations

“…To place our constraints, we make use of the point source search results reported in [21] together with the diffuse flux characterisation detailed in [22,23], as these are based on the same underlying event sample. This analysis is detailed in [3], with the code also available as the nu_pop GitHub repository . Here, we briefly summarise the resulting constraints in Figure 2, for the case of two priors on the source density evolution, encompassing both plausible positive and negative evolutions.…”

“…These ideas can also be applied to other multi-messenger associations. A full exposition can be found in [3] and [4], but we present some motivating factors and simplified calculations in this work. In Section 2, we discuss developments in the statistical methods used to evaluate individual source-event coincidences and how more information can be brought into the analysis.…”