Abstracts of Interest
Selected by:
Ryan Burley
Abstract: 2501.05569
Full Text: [ PostScript, PDF]
Full Text: [ PostScript, PDF]
Title:Space-based Ultra-High Energy Cosmic-Ray Experiments
View PDF HTML (experimental)Abstract:Space-based experiments, either orbiting the Earth or from scientific balloon altitudes, measure high-energy cosmic rays by measuring from above the atmosphere the optical and radio signals generated by extensive air showers (EAS). These experiments are designed to have a large field-of-view (FoV) for observing EAS which translates to monitoring the atmosphere over a large, $\sim 10^6$ km$^2$ area on the ground. Ultra-high energy cosmic rays (UHECRs, $E_{CR} > ~\sim 1$ EeV) are measured by using the isotropic near-UV air fluorescence signal to finely sample the EAS development and to efficiently use the atmosphere as a vast calorimeter. At UHE, these immense EAS particle cascades have sufficient charged particle content to generate the relatively dim fluorescence light that propagates to the space-based instrument. Additionally, the beamed Cherenkov light and geomagnetic radio emission from EAS arrive with $> ~\sim 10$ ns impulse and are measured at small angles away from the cosmic ray trajectories. In particular for optical Cherenkov measurements, the energy thresholds can be $> ~\sim 1$ PeV, i.e. for very-high energy cosmic rays (VHECRs). ...
In this chapter, the nature of observing the UHECR-induced shower development from orbiting and balloon-borne experiments is detailed, both for missions that have been flown and those currently in development. This will be accomplished by discussing experimental performance in terms of measuring the UHECR spectrum, UHECR nuclear composition, and UHECR arrival direction. The ability for these experiments to also perform VHECR and VHE and UHE cosmic neutrino measurements will also be discussed.
Abstract: 2501.05581
Full Text: [ PostScript, PDF]
Full Text: [ PostScript, PDF]
Title:More than a void? The detection and characterization of cavities in a simulated galaxy's interstellar medium
View PDF HTML (experimental)Abstract:The interstellar medium of galaxies is filled with holes, bubbles, and shells, typically interpreted as remnants of stellar evolution. There is growing interest in the study of their properties to investigate stellar and supernova feedback. So far, the detection of cavities in observational and numerical data is mostly done visually and, hence, is prone to biases. Therefore, we present an automated, objective method for discovering cavities in particle simulations, with demonstrations using hydrodynamical simulations of a dwarf galaxy. The suggested technique extracts holes based on the persistent homology of particle positions and identifies tight boundary points around each. With a synthetic ground-truth analysis, we investigate the relationship between data density and the detection radius, demonstrating that higher data density also allows for the robust detection of smaller cavities. By tracking the boundary points, we can measure the shape and physical properties of the cavity, such as its temperature. In this contribution, we detect 808 holes in 21 simulation snapshots. We classified the holes into supernova-blown bubbles and cavities unrelated to stellar feedback activity based on their temperature profile and expansion behaviour during the 100 million years covered by the simulation snapshots analysed for this work. Surprisingly, less than 40% of the detected cavities can unequivocally be linked to stellar evolution. Moreover, about 36% of the cavities are contracting, while 59% are expanding. The rest do not change for a few million years. Clearly, it is erroneous to interpret observational data based on the premise that all cavities are supernova-related and expanding. This study reveals that supernova-driven bubbles typically exhibit smaller diameters, larger expansion velocities, and lower kinetic ages (with a maximum of 220 million years) compared to other cavities.
Abstract: 2501.05692
Full Text: [ PostScript, PDF]
Full Text: [ PostScript, PDF]
Title:Astrophysical Narratives: Poetic Representations of Gamma-Ray Emission from FermiLAT via Markov Chains
View PDF HTML (experimental)Abstract:The intersection of art and science offers novel ways to interpret and represent complex phenomena. This project explores the convergence of high-energy astrophysics, concrete poetry, and natural language processing (NLP) by proposing a Markov chain-based algorithm that generates poetic texts from gamma-ray emission maps of the universe. Gamma rays, the most energetic form of electromagnetic radiation, arise from violent astrophysical processes such as supernovae, pulsars, and black hole accretion, observable through instruments like the \textit{Fermi Large Area Telescope} (FermiLAT). These high-energy events are mapped and processed into matrices, treated as Markov chains, where each state's transition probability is determined by the intensity of gamma-ray sources in a region of interest.
Abstract: 2501.05725
Full Text: [ PostScript, PDF]
Full Text: [ PostScript, PDF]
Title:Expanding Molecular Shell and Possible γ-ray Source Associated with Supernova Remnant Kesteven 67
View PDF HTML (experimental)Abstract:We investigate the molecular environment of the supernova remnant (SNR) Kesteven 67 (G18.8+0.3) using observations in $^{12}$CO, $^{13}$CO, HCO$^+$,and HCN lines and possible associated $\gamma$-ray emission using 16-yr Fermi-LAT observation. We find that the SNR is closely surrounded by a molecular belt in the southeastern boundary, with the both recessed in the band-like molecular gas structure along the Galactic plane. The asymmetric molecular line profiles are widely present in the surrounding gas around local-standard-of-rest velocity +20 km s$^{-1}$. The secondary components centered at $\sim$+16km s$^{-1}$ in the belt and $\sim$+26 km s$^{-1}$ in the northern clump can be ascribed to the motion of a wind-blown molecular shell. This explanation is supported by the position-velocity diagram along a line cutting across the remnant, which shows an arc-like pattern, suggesting an expanding gas structure. With the simulation of chemical effects of shock propagation, the abundance ratios $N$(HCO$^+$)/$N$($^{12}$CO) $\sim2.6\times 10^{-5}$--$3.6\times 10^{-4}$ obtained in the belt can be more naturally interpreted by the wind-driven bubble shock than by the SNR shock. The belt and northern clump are very likely to be parts of an incomplete molecular shell of bubble driven by O-type progenitor star's wind. The analysis of 0.2--500 GeV $\gamma$-ray emission uncovers a possible point source (`Source~A') about 6.5$\sigma$ located in the north of the SNR, which essentially corresponds to northern molecular clump. Our spectral fit of the emission indicates that a hadronic origin is favored by the measured Galactic number ratio between CR electrons and protons $\sim0.01$.
Abstract: 2501.05944
Full Text: [ PostScript, PDF]
Full Text: [ PostScript, PDF]
Title:Modeling the Saddle-like GeV-TeV Spectrum of HESS J1809-193: $γ$-Rays Arising from Reverse-Shocked Pulsar Wind Nebula?
View PDF HTML (experimental)Abstract:Evolution of pulsar wind nebulae (PWNe) could be expected to leave imprints in $\gamma$-rays. We suggest that intriguing GeV-TeV spectral energy distribution (SED) of HESS J1809$-$193 and Fermi-LAT source J1810.3$-$1925e is very likely to be the $\gamma$-ray signature of PWN J1809$-$193 in light of the scenario that the PWN was struck by the reverse shock of the parent supernova remnant. Based on evolutionary theory of PWNe, we consider that, when the PWN was disrupted during collision by the reverse shock, some very high-energy electrons escaped impulsively. The remaining electrons stayed in the relic PWN, which was displaced from the pulsar. The very high-energy part of the remaining electrons were depleted by the strong magnetic field that was enhanced by the reverse shock compression in the reverberation stage, leaving the other part of them generating GeV emission. The particles injected from the pulsar after the disruption enter the relic PWN through the newly formed tunnel called the cocoon. The $\gamma$-ray emission from the escaped electrons can account for the TeV spectrum of component A of HESS J1809$-$193 or the TeV halo, while the electrons remaining after disruption can account for the GeV spectrum of J1810.3$-$1925e. Thus, combination of contributions from these two populations of electrons naturally reproduces the saddle-like SED of HESS J1809$-$193 and J1810.3$-$1925e from 5 GeV to 30 TeV, together with the spectral hardening around 100 GeV. We also show that the post-disruption injection of electrons can explain the spectrum of the relatively faint $\gamma$-ray emission of component B of HESS J1809$-$193.
Abstract: 2501.06011
Full Text: [ PostScript, PDF]
Full Text: [ PostScript, PDF]
Title:SECRET: Stochasticity Emulator for Cosmic Ray Electrons
View PDF HTML (experimental)Abstract:The spectrum of cosmic-ray electrons depends sensitively on the history and spatial distribution of nearby sources. Given our limited observational handle on cosmic-ray sources, any model remains necessarily probabilistic. Previously, predictions were performed in a Monte Carlo fashion, summing the contributions from individual, simulated sources to generate samples from the statistical ensemble of possible electron spectra. Such simulations need to be re-run if the cosmic-ray transport parameters (e.g. diffusion coefficient, maximum energy) are changed, rendering any parameter study computationally expensive. In addition, a proper statistical analysis of observations and comparison with such probabilistic models requires the joint probability distribution of the full spectrum instead of only samples. Note that parametrising this joint distribution is rendered difficult by the non-Gaussian statistics of the cosmic-ray fluxes. Here, we employ machine learning to compute the joint probability distribution of cosmic-ray electron fluxes. Specifically, we employ masked autoregressive density estimation (MADE) for a representation of the high-dimensional joint probability distribution. In a first step, we train the network on a Monte Carlo simulation for a fixed set of transport parameters, thus significantly accelerating the generation of samples. In a second step, we extend this setup to SECRET (Stochasticity Emulator for Cosmic Ray Electrons), allowing to reliably interpolate over the space of transport parameters. We make the MADE and SECRET codes available at this https URL .
Abstract: 2501.06677
Full Text: [ PostScript, PDF]
Full Text: [ PostScript, PDF]
Title:Origin likelihood functions for extreme-energy cosmic rays
View PDF HTML (experimental)Abstract:Unlike neutrinos and photons arriving from extra-galactic sources, ultra-high energy cosmic rays (UHECRs) do not trace back to their origins due to propagation effects such as magnetic deflections and energy losses. For ankle energies, UHECRs can propagate for hundreds of megaparsecs with negligible energy losses but the directional information is lost after a few megaparsecs. On the other hand, at the highest energies the directions are kept for larger distances due to the increased rigidity but the interaction rates with the cosmic microwave background strongly suppress the cosmic rays within a few to tens of megaparsecs. Therefore, UHECRs with energies $E > 10^{20}$ eV (extreme-energy cosmic rays (ExECRs)) such as the Amaterasu event recently reported by Telescope Array, are of particular interest to identify the sources within our galactic neighborhood. However, photonuclear interactions are stochastic in nature and produce changes in the nuclear species emitted, which makes it difficult the task of estimating the likelihood distribution of its origin. This work discusses a novel procedure to estimate the likelihood of the origin for extreme-energy cosmic rays based on probability distributions for UHECR stochastic interactions. The method is applied to the Amaterasu event and compared to recently published works which employ Monte Carlo codes (e.g. CRPropa) in their analysis. The advantages of the method presented here are demonstrated by the increased resolution and the ease of computation unlike other approaches employed so far. The results presented indicate that the localization of the origin of extreme energy cosmic rays could be possible in some cases without knowledge of the original composition.
Abstract: 2501.06257
Full Text: [ PostScript, PDF]
Full Text: [ PostScript, PDF]
Title:Resolution Limiting Factors in Low-Energy Cascade Zenith Reconstruction with the IceCube Upgrade
View PDF HTML (experimental)Abstract:The IceCube Neutrino Observatory includes low energy extensions such as the existing DeepCore subarray and the upcoming IceCube Upgrade, which will consist of seven new strings of photosensors with denser instrumentation than the existing array. The setup will allow for the study of neutrino oscillations with greater sensitivity compared to the existing instrumentation, improve neutrino mass ordering studies, and test for the unitarity of the PMNS mixing matrix with high precision. A critical component in these low-energy physics analyses is the accurate reconstruction of event information, particularly the zenith angle of incoming neutrinos. In this study, we discuss the processes that limit the zenith resolution, which include the transverse spread of the hadronic shower, in-ice photon scattering, module resolutions, and module noise. By considering approximations to these processes, we aim to approach the intrinsic zenith resolution limits for purely hadronic events.
Abstract: 2501.08671
Full Text: [ PostScript, PDF]
Full Text: [ PostScript, PDF]
Title:Improvements to monoscopic analysis for imaging atmospheric Cherenkov telescopes: Application to H.E.S.S
View PDF HTML (experimental)Abstract:Imaging atmospheric Cherenkov telescopes (IACTs) detect gamma rays by measuring the Cherenkov light emitted by secondary particles in the air shower when the gamma rays hit the atmosphere. At low energies, the limited amount of Cherenkov light produced typically implies that the event is registered by one IACT only. Such events are called monoscopic events, and their analysis is particularly difficult. Challenges include the reconstruction of the event's arrival direction, energy, and the rejection of background events. Here, we present a set of improvements, including a machine-learning algorithm to determine the correct orientation of the image, an intensity-dependent selection cut that ensures optimal performance, and a collection of new image parameters. To quantify these improvements, we use the central telescope of the H.E.S.S. IACT array. Knowing the correct image orientation, which corresponds to the arrival direction of the photon in the camera frame, is especially important for the angular reconstruction, which could be improved in resolution by 57% at 100 GeV. The event selection cut, which now depends on the total measured intensity of the events, leads to a reduction of the low-energy threshold for source analyses by ~50%. The new image parameters characterize the intensity and time distribution within the recorded images and complement the traditionally used Hillas parameters in the machine learning algorithms. We evaluate their importance to the algorithms in a systematic approach and carefully evaluate associated systematic uncertainties. We find that including subsets of the new variables in machine-learning algorithms improves the reconstruction and background rejection, resulting in a sensitivity improved by 41% at the low-energy threshold.
Abstract: 2501.08957
Full Text: [ PostScript, PDF]
Full Text: [ PostScript, PDF]
Title:Potential Contribution of Young Pulsar Wind Nebulae to Galactic High-Energy Neutrino Emission
View PDF HTML (experimental)Abstract:Pulsar wind nebulae (PWNe), especially the young ones, are among the most energetic astrophysical sources in the Galaxy. It is usually believed that the spin-down energy injected from the pulsars is converted into magnetic field and relativistic electrons, but the possible presence of proton acceleration inside PWNe cannot be ruled out. Previous works have estimated the neutrino emission from PWNe using various source catalogs measured in gamma-rays. However, such results rely on the sensitivity of TeV gamma-ray observations and may omit the contribution by unresolved sources. Here we estimate the potential neutrino emission from a synthetic population of PWNe in the Galaxy with a focus on the ones that are still in the free expansion phase. In the calculation, we model the temporal evolution of the free-expanding PWNe and consider the transport of protons inside the PWNe. The Crab nebula is treated as a standard template for young PWNe to evaluate some model parameters, such as the energy conversion fraction of relativistic protons and the target gas density for the hadronic process, which are relevant to neutrino production. In the optimistic case, the neutrino flux from the simulated young PWNe may constitute to 5% of the measured flux by IceCube around 100 TeV. At higher energy around 1 PeV, the neutrino emission from the population highly depends on the injection spectral shape, and also on the emission of the nearby prominent sources.
Abstract: 2501.09108
Full Text: [ PostScript, PDF]
Full Text: [ PostScript, PDF]
Title:Blazars Jets and prospects for TeV-PeV neutrinos & gamma-rays through cosmic-ray interactions
View PDF HTML (experimental)Abstract:This study explores the origins of cosmic rays and their secondary messengers, focusing on the potential role of four BL Lacs W Comae, 1ES 1959+650, PKS 2005-489, and PKS 2155-304 as potential sources of astrophysical neutrinos and gamma rays. We analyzed a single-zone model to understand the interactions between high-energy protons and ambient photons within blazar jets, leading to neutrino production observables and gamma-ray emission. This modeling contextualizes the emissions within multiwavelength observations and evaluates the capabilities of the next-generation Cherenkov Telescope Array Observatory (CTAO) in detecting these emissions. Our estimations suggest that these sources could be effective emitters of CRs, highlighting the need for future multimessenger observations to further investigate and constrain this class of sources.
Abstract: 2501.09276
Full Text: [ PostScript, PDF]
Full Text: [ PostScript, PDF]
Title:Search for neutrino doublets and triplets using 11.4 years of IceCube data
View PDF HTML (experimental)Abstract:We report a search for high-energy astrophysical neutrino multiplets, detections of multiple neutrino clusters in the same direction within 30 days, based on an analysis of 11.4 years of IceCube data. A new search method optimized for transient neutrino emission with a monthly time scale is employed, providing a higher sensitivity to neutrino fluxes. This result is sensitive to neutrino transient emission, reaching per-flavor flux of approximately $10^{-10}\ {\rm erg}\ {\rm cm}^{-2}\ {\rm sec}^{-1}$ from the Northern sky in the energy range $E\gtrsim 50$~TeV. The number of doublets and triplets identified in this search is compatible with the atmospheric background hypothesis, which leads us to set limits on the nature of neutrino transient sources with emission timescales of one month.
Abstract: 2501.09594
Full Text: [ PostScript, PDF]
Full Text: [ PostScript, PDF]
Title:Constraints on Cosmic Rays Acceleration in Bright Gamma-ray Bursts with Observations of Fermi
View PDFAbstract:Gamma-ray bursts (GRBs) are widely suggested as potential sources of ultrahigh-energy cosmic rays (UHECRs). The kinetic energy of the jets dissipates, leading to the production of an enormous amount of $\gamma$-ray photons and possibly also the acceleration of protons. The accelerated protons will interact with the radiation of the GRB via the photomeson and Bethe-Heitler processes, which can initiate electromagnetic cascades. This process can give rise to broadband radiation up to the GeV-TeV $\gamma$-ray regime. The expected $\gamma$-ray flux from cascades depends on properties of the GRB jet, such as the dissipation radius $R_{\rm diss}$, the bulk Lorentz factor $\Gamma$, and the baryon loading factor $\eta_p$. Therefore, observations of Fermi-LAT can impose constraints on these important parameters. In this study, we select 12 GRBs of high keV-MeV fluence and constrain the baryon loading factor, under different combinations of the bulk Lorentz factor and the dissipation radius based on Fermi-LAT's measurements. Our findings indicate a strong constraint of $\eta_p<10$ for most selected GRBs over a large parameter space except for large dissipation radii ($\gtrsim 10^{15}\rm cm$) and high bulk Lorentz factors ($\gtrsim 600$). The constraint is comparable to, and in some GRBs even stronger than, that from high-energy neutrinos for stacked GRBs. Our results suggest that for typical bulk Lorentz factor of several hundreds, the dissipation radii of GRBs need be large to avoid overshooting the GeV gamma-ray flux during the prompt emission phase of GRBs, which can be used to constrain GRBs.
This page created: Mon Jan 27 10:29:50 ACDT 2025 by rburley
For a printable title listing click here
For details on generating this page see the instructions. If there are problems with this page contact Violet.
For previous lists of abstracts of interest click Previous abstracts of interest