Search for Sources of High Energy Neutrons with Four Years of Data from the IceTop Detector

TL;DR

This study uses four years of IceTop data to search for high-energy neutron sources in the Galaxy, but finds no significant excess or correlation, setting upper limits on fluxes and constraining models.

Contribution

First comprehensive four-year search for Galactic high-energy neutron sources using IceTop data, including all-sky and targeted analyses, with flux limits to inform source models.

Findings

No significant excess detected in all-sky search.

No significant correlation with candidate sources.

Flux upper limits constrain Galactic neutron production.

Abstract

IceTop is an air shower array located on the Antarctic ice sheet at the geographic South Pole. IceTop can detect an astrophysical flux of neutrons from Galactic sources as an excess of cosmic ray air showers arriving from the source direction. Neutrons are undeflected by the Galactic magnetic field and can typically travel 10 ($E$ / PeV) pc before decay. Two searches are performed using 4 years of the IceTop dataset to look for a statistically significant excess of events with energies above 10 PeV ($10^{16}$ eV) arriving within a small solid angle. The all-sky search method covers from -90$^{\circ}$ to approximately -50$^{\circ}$ in declination. No significant excess is found. A targeted search is also performed, looking for significant correlation with candidate sources in different target sets. This search uses a higher energy cut (100 PeV) since most target objects lie beyond 1 kpc. The target sets include pulsars with confirmed TeV energy photon fluxes and high-mass X-ray binaries. No significant correlation is found for any target set. Flux upper limits are determined for both searches, which can constrain Galactic neutron sources and production scenarios.