The cumulative emission resulting from hadronic cosmic-ray interactions in star-forming galaxies (SFGs) has been proposed as the dominant contribution to the astrophysical neutrino flux at TeV to PeV ...energies reported by IceCube. The same particle interactions also inevitably create γ-ray emission that could be detectable as a component of the extragalactic γ-ray background (EGB), which is now measured with the Fermi-LAT in the energy range from 0.1 to 820 GeV. New studies of the blazar flux distribution at γ-ray energies above 50 GeV place an upper bound on the residual non-blazar component of the EGB. We show that these results are in strong tension with models that consider SFGs as the dominant source of the diffuse neutrino backgrounds. A characteristic spectral index for parent cosmic rays in starburst galaxies of ΓSB 2.3 for dN / dE ∝ E − Γ SB is consistent with the observed scaling relation between γ-ray and IR luminosity for SFGs, the bounds from the non-blazar EGB, and the observed γ-ray spectra of individual starbursts, but underpredicts the IceCube data by approximately an order of magnitude.
ABSTRACT We estimate the conventional astrophysical emission from dwarf spheroidal satellite galaxies (dSphs) of the Milky Way (MW), focusing on millisecond pulsars (MSPs), and evaluate the potential ...for confusion with dark matter (DM) annihilation signatures at GeV energies. In low-density stellar environments, such as dSphs, the abundance of MSPs is expected to be proportional to stellar mass. Accordingly, we construct the γ-ray luminosity function (LF) of MSPs in the MW disk, where >90 individual MSPs have been detected with the Fermi Large Area Telescope (LAT), and scale this LF to the stellar masses of 30 dSphs to estimate the cumulative emission from their MSP populations. We predict that MSPs within the highest stellar mass dSphs, Fornax and Sculptor, produce a γ-ray flux >500 MeV of ∼10−11 ph cm−2 s−1, which is a factor ∼10 below the current LAT sensitivity at high Galactic latitudes. The MSP emission in ultra-faint dSphs, including targets with the largest J-factors, is typically several orders of magnitude lower, suggesting that these targets will remain clean targets for indirect DM searches in the foreseeable future. For a DM particle of mass 25 GeV annihilating to b quarks at the thermal relic cross section (consistent with DM interpretations of the Galactic Center excess), we find that the expected γ-ray emission due to DM exceeds that of MSPs in all of the target dSphs. Using the same MW MSP population model, we also estimate the Galactic foreground MSP coincidence probability along the same sightlines to the dSphs.
Abstract Galactic and extragalactic objects in the Universe are sources of high-energy neutrinos that may contribute to the astrophysical neutrino signal seen by IceCube. Recently, a study done using ...cascade-like events seen by IceCube reported neutrino emission from the Galactic plane with >4 σ significance. In this work, we put a lower limit on the number of Galactic sources required to explain this emission. To achieve this, we use a simulation package created to simulate point sources in the Galaxy along with the neutrino and gamma-ray flux emissions originating from them. Along with using past IceCube discovery potential curves, we also account for Eddington bias effects due to Poisson fluctuations in the number of detected neutrino events. We present a toy Monte Carlo simulation to show that there must be at least eight sources, each with luminosity less than 1.6 × 10 35 erg s −1 , responsible for the Galactic neutrino emission. Our results constrain the number of individual point-like emission regions, which apply both to discrete astrophysical sources and to individual points of diffuse emission.
A new measurement of a spatially extended gamma-ray signal from the center of the Andromeda galaxy (M31) has recently been published by the Fermi-LAT collaboration, reporting that the emission ...broadly resembles the so-called Galactic center excess (GCE) of the Milky Way (MW). The weight of the evidence is steadily accumulating on a millisecond pulsar (MSPs) origin for the GCE. These elements prompt us to compare these observations with what is, perhaps, the simplest model for an MSP population, which is solely obtained by rescaling of the MSP luminosity function that is determined in the local MW disk via the respective stellar mass of the systems. Remarkably, we find that without free fitting parameters, this model can account for both the energetics and the morphology of the GCE within uncertainties. For M31, the estimated luminosity due to primordial MSPs is expected to only contribute about a quarter of the detected emission, although a stronger contribution cannot be excluded given the large uncertainties. If correct, the model predicts that the M31 disk emission due to MSPs is not far below the present upper bound. We also discuss additional refinements of this simple model. Using the correlation between globular cluster gamma-ray luminosity and stellar encounter rate, we gauge the dynamical MSP formation in the bulge. This component is expected to contribute to the GCE only at a level of 5%, it could affect the signal's morphology. We also comment on the limitations of our model and on future perspectives for improved diagnostics.
In the past decade IceCube's observations have revealed a flux of astrophysical neutrinos extending to 107GeV. The forthcoming generation of neutrino observatories promises to grant further insight ...into the high-energy neutrino sky, with sensitivity reaching energies up to 1012GeV. At such high energies, a new set of effects becomes relevant, which was not accounted for in the last generation of neutrino propagation software. Thus, it is important to develop new simulations which efficiently and accurately model lepton behavior at this scale. We present TauRunner, a Python-based package that propagates neutral and charged leptons. TauRunner supports propagation between 10GeV and 1012GeV. The package accounts for all relevant secondary neutrinos produced in charged-current tau neutrino interactions. Additionally, tau energy losses of taus produced in neutrino interactions are taken into account, and treated stochastically. Finally, TauRunner is broadly adaptable to divers experimental setups, allowing for user-specified trajectories and propagation media, neutrino cross sections, and initial spectra.
Program title:TauRunner
CPC Library link to program files:https://doi.org/10.17632/82nyd9skhj.1
Developer's repository link:https://github.com/icecube/TauRunner
Licensing provisions: GNU General Public License 3
Programming language:Python
Nature of problem: Propagation of ultra-high energy neutrinos in dense media accounting for various effects associated with ντ and τ± energy losses.
Solution method: Monte Carlo methods.
We present a search for neutrinos in coincidence in time and direction with four fast radio bursts (FRBs) detected by the Parkes and Green Bank radio telescopes during the first year of operation of ...the complete IceCube Neutrino Observatory (2011 May through 2012 May). The neutrino sample consists of 138,322 muon neutrino candidate events, which are dominated by atmospheric neutrinos and atmospheric muons but also contain an astrophysical neutrino component. Considering only neutrinos detected on the same day as each FRB, zero IceCube events were found to be compatible with the FRB directions within the estimated 99% error radius of the neutrino directions. Based on the non-detection, we present the first upper limits on the neutrino fluence from FRBs.
South Pole ice is predicted to be the best medium for acoustic neutrino detection. Moreover, ice is the only medium in which all three dense-medium detection methods (optical, radio, and acoustic) ...can be used to monitor the same interaction volume. Events detected in coincidence between two methods allow significant background rejection confidence, which is necessary to study rare GZK neutrinos. In 2007 and 2008 the South Pole Acoustic Test Setup (SPATS) was installed as a research and development project associated with the IceCube experiment. The purpose of SPATS is to measure the acoustic ice properties at the South Pole in order to determine the feasibility of a future large hybrid array. The deployment and performance of SPATS are described, as are first results and work in progress on the sound speed, background noise, and attenuation.
We present a deep learning, computer vision algorithm constructed for the purposes of identifying and classifying charged particles in camera image sensors. We apply our algorithm to data collected ...by the Distributed Electronic Cosmic-ray Observatory (DECO), a global network of smartphones that monitors camera image sensors for the signatures of cosmic rays and other energetic particles, such as those produced by radioactive decays. The algorithm, whose core component is a convolutional neural network, achieves classification performance comparable to human quality across four distinct DECO event topologies. We apply our model to the entire DECO data set and determine a selection that achieves ≥ 90% purity for all event types. In particular, we estimate a purity of 95% when applied to cosmic-ray muons. The automated classification is run on the public DECO data set in real time in order to provide classified particle interaction images to users of the app and other interested members of the public.
PDF
