arXiv subjects

D. Góra

Publications and source records attributed to D. Góra.

At least 19 recordsLinked to original sources

arXiv2024

An improved method to search for flares from point sources of ultra-high-energy photons

Flares produced by certain classes of astrophysical objects may be sources of some ultra-high-energy particles, which, if they are photons, would group into clusters of events correlated in space and time. Identification of such clustering in cosmic-ray data would provide important evidence for possible existence of ultra-high-energy (UHE) photons and could potentially help identify their sources. We present an analysis method to search for space-time clustering of ultra-high-energy extensive air showers, namely the stacking method, which combines a time-clustering algorithm with an unbinned likelihood study. In addition, to enhance the capability to discriminate between signal (photon-initiated events) and background (hadron-initiated) events, we apply a photon tag. This involves using relevant probability distribution functions to classify each event as more likely to be either a photon or a hadron. We demonstrate that the stacking method can effectively distinguish between events initiated by photons and those initiated by hadrons (background). The number of photon events in a data sample, as well as the flare(s) duration can also be retrieved correctly. The stacking method with a photon tag requires only a few events to identify a photon flare. This method can be used to search for the cosmic ray sources and/or improve limits on the fluxes of UHE photons.

astro-ph.HE↗

arXiv2018

Cosmic-Ray Extremely Distributed Observatory: status and perspectives

The Cosmic-Ray Extremely Distributed Observatory (CREDO) is a project dedicated to global studies of extremely extended cosmic-ray phenomena, the cosmic-ray ensembles (CRE), beyond the capabilities of existing detectors and observatories. Up to date cosmic-ray research has been focused on detecting single air showers, while the search for ensembles of cosmic-rays, which may overspread a significant fraction of the Earth, is a scientific terra incognita. Instead of developing and commissioning a completely new global detector infrastructure, CREDO proposes approaching the global cosmic-ray analysis objectives with all types of available detectors, from professional to pocket size, merged into a worldwide network. With such a network it is possible to search for evidences of correlated cosmic-ray ensembles. One of the observables that can be investigated in CREDO is a number of spatially isolated events collected in a small time window which could shed light on fundamental physics issues. The CREDO mission and strategy requires active engagement of a large number of participants, also non-experts, who will contribute to the project by using common electronic devices (e.g. smartphones). In this note the status and perspectives of the project is presented.

astro-ph.IM↗

arXiv2018

Cosmic Ray Extremely Distributed Observatory: a global network of detectors to probe contemporary physics mysteries

In the past few years, cosmic-rays beyond the GZK cut-off ($E > 5 \times 10^{19}$ eV) have been detected by leading collaborations such as Pierre Auger Observatory. Such observations raise many questions as to how such energies can be reached and what source can possibly produce them. Although at lower energies, mechanisms such as Fermi acceleration in supernovae front shocks seem to be favored, top-down scenarios have been proposed to explain the existence of ultra-high energy cosmic-rays: the decay of super-massive long-lived particles produced in the early Universe may yield to a flux of ultra-high energy photons. Such photons might be presently generating so called super-preshowers, an extended cosmic-ray shower with a spatial distribution that can be as wide as the Earth diameter. The Cosmic Ray Extremely Distributed Observatory (CREDO) mission is to find such events by means of a network of detectors spread around the globe. CREDO's strategy is to connect existing detectors and create a worldwide network of cosmic-ray observatories. Moreover, citizen-science constitutes an important pillar of our approach. By helping our algorithms to recognize detection patterns and by using smartphones as individual cosmic-ray detectors, non-scientists can participate in scientific discoveries and help unravel some of the deepest mysteries in physics.

astro-ph.IM↗

arXiv2018

Limits on the flux of tau neutrinos from 1 PeV to 3 EeV with the MAGIC telescopes

A search for tau neutrino induced showers with the MAGIC telescopes is presented. The MAGIC telescopes located at an altitude of 2200 m a.s.l. in the Canary Island of La Palma, can point towards the horizon or a few degrees below across an azimuthal range of about 80 degrees. This provides a possibility to search for air showers induced by tau leptons arising from interactions of tau neutrinos in the Earth crust or the surrounding ocean. In this paper we show how such air showers can be discriminated from the background of very inclined hadronic showers by using Monte Carlo simulations. Taking into account the orography of the site, the point source acceptance and the event rates expected have been calculated for a sample of generic neutrino fluxes from photo-hadronic interactions in AGNs. The analysis of about 30 hours of data taken towards the sealeads to a 90\% C.L. point source limit for tau neutrinos in the energy range from $1.0 \times 10^{15}$ eV to $3.0 \times 10^{18}$ eV of about $E_{ν_τ}^{2}\times ϕ(E_{ν_τ}) < 2.0 \times 10^{-4}$ GeV cm$^{-2}$ s$^{-1}$ for an assumed power-law neutrino spectrum with spectral index $γ$=-2. However, with 300 hours and in case of an optimistic neutrino flare model, limits of the level down to $E_{ν_τ}^{2}\times ϕ(E_{ν_τ}) < 8.4 \times 10^{-6}$ GeV cm$^{-2}$ s$^{-1}$ can be expected.

astro-ph.IM↗

arXiv2018

Search for Extensive Photon Cascades with the Cosmic-Ray Extremely Distributed Observatory

Although the photon structure is most efficiently studied with the accelerator instruments, there is also a scientifically complementary potential in investigations on photons produced in the outer space. This potential is already being explored with gamma ray telescopes, ultra-high energy cosmic ray observatories and, since very recently, by the Cosmic-Ray Extremely Distributed Observatory (CREDO). Unlike the former instruments focused on detection of single photons, CREDO aims at the detection of cascades (ensembles) of photons originating even at astrophysical distances. If at least a part of such a cascade reaches Earth, it might produce a unique pattern composed of a number of air showers observable by an appropriately dense array of standard detectors. If the energies of air showers constituting the pattern are relatively low and if the typical distances between the neighbors are large, the ensemble character of the whole phenomenon might remain uncovered, unless the CREDO strategy is implemented.

astro-ph.IM↗

arXiv2018

Cosmic-Ray Extremely Distributed Observatory: a global cosmic ray detection framework

The main objective of the Cosmic-Ray Extremely Distributed Observatory (CREDO) is the detection and analysis of extended cosmic ray phenomena, so-called super-preshowers (SPS), using existing as well as new infrastructure (cosmic-ray observatories, educational detectors, single detectors etc.). The search for ensembles of cosmic ray events initiated by SPS is yet an untouched ground, in contrast to the current state-of-the-art analysis, which is focused on the detection of single cosmic ray events. Theoretical explanation of SPS could be given either within classical (e.g., photon-photon interaction) or exotic (e.g., Super Heavy Dark Matter decay or annihilation) scenarios, thus detection of SPS would provide a better understanding of particle physics, high energy astrophysics and cosmology. The ensembles of cosmic rays can be classified based on the spatial and temporal extent of particles constituting the ensemble. Some classes of SPS are predicted to have huge spatial distribution, a unique signature detectable only with a facility of the global size. Since development and commissioning of a completely new facility with such requirements is economically unwarranted and time-consuming, the global analysis goals are achievable when all types of existing detectors are merged into a worldwide network. The idea to use the instruments in operation is based on a novel trigger algorithm: in parallel to looking for neighbour surface detectors receiving the signal simultaneously, one should also look for spatially isolated stations clustered in a small time window.

astro-ph.IM↗

arXiv2016

Search for correlations between the arrival directions of IceCube neutrino events and ultrahigh-energy cosmic rays detected by the Pierre Auger Observatory and the Telescope Array

This paper presents the results of different searches for correlations between very high-energy neutrino candidates detected by IceCube and the highest-energy cosmic rays measured by the Pierre Auger Observatory and the Telescope Array. We first consider samples of cascade neutrino events and of high-energy neutrino-induced muon tracks, which provided evidence for a neutrino flux of astrophysical origin, and study their cross-correlation with the ultrahigh-energy cosmic ray (UHECR) samples as a function of angular separation. We also study their possible directional correlations using a likelihood method stacking the neutrino arrival directions and adopting different assumptions on the size of the UHECR magnetic deflections. Finally, we perform another likelihood analysis stacking the UHECR directions and using a sample of through-going muon tracks optimized for neutrino point-source searches with sub-degree angular resolution. No indications of correlations at discovery level are obtained for any of the searches performed. The smallest of the p-values comes from the search for correlation between UHECRs with IceCube high-energy cascades, a result that should continue to be monitored.

astro-ph.HE↗

arXiv2015

Searches for Relativistic Magnetic Monopoles in IceCube

Various extensions of the Standard Model motivate the existence of stable magnetic monopoles that could have been created during an early high-energy epoch of the Universe. These primordial magnetic monopoles would be gradually accelerated by cosmic magnetic fields and could reach high velocities that make them visible in Cherenkov detectors such as IceCube. Equivalently to electrically charged particles, magnetic monopoles produce direct and indirect Cherenkov light while traversing through matter at relativistic velocities. This paper describes searches for relativistic (v>0.76c) and mildly relativistic (v>0.51c) monopoles, each using one year of data taken in 2008/09 and 2011/12 respectively. No monopole candidate was detected. For a velocity above 0.51c the monopole flux is constrained down to a level of 1.55x10^-18 cm-2 s-1 sr-1. This is an improvement of almost two orders of magnitude over previous limits.

astro-ph.HE↗

arXiv2015

Search for dark matter annihilations in the Sun with the 79-string IceCube detector

We have performed a search for muon neutrinos from dark matter annihilation in the center of the Sun with the 79-string configuration of the IceCube neutrino telescope. For the first time, the DeepCore sub-array is included in the analysis, lowering the energy threshold and extending the search to the austral summer. The 317 days of data collected between June 2010 and May 2011 are consistent with the expected background from atmospheric muons and neutrinos. Upper limits are therefore set on the dark matter annihilation rate, with conversions to limits on spin-dependent and spin-independent WIMP-proton cross-sections for WIMP masses in the range 20 - 5000 GeV. These are the most stringent spin-dependent WIMP-proton cross-sections limits to date above 35 GeV.

astro-ph.HE↗

arXiv2015

Detection of a Type IIn Supernova in Optical Follow-up Observations of IceCube Neutrino Events

The IceCube neutrino observatory pursues a follow-up program selecting interesting neutrino events in real-time and issuing alerts for electromagnetic follow-up observations. In March 2012, the most significant neutrino alert during the first three years of operation was issued by IceCube. In the follow-up observations performed by the Palomar Transient Factory (PTF), a Type IIn supernova (SN) PTF12csy was found $0.2^\circ$ away from the neutrino alert direction, with an error radius of $0.54^\circ$. It has a redshift of $z=0.0684$, corresponding to a luminosity distance of about $300 \, \mathrm{Mpc}$ and the Pan-STARRS1 survey shows that its explosion time was at least 158 days (in host galaxy rest frame) before the neutrino alert, so that a causal connection is unlikely. The a posteriori significance of the chance detection of both the neutrinos and the SN at any epoch is $2.2 \, σ$ within IceCube's 2011/12 data acquisition season. Also, a complementary neutrino analysis reveals no long-term signal over the course of one year. Therefore, we consider the SN detection coincidental and the neutrinos uncorrelated to the SN. However, the SN is unusual and interesting by itself: It is luminous and energetic, bearing strong resemblance to the SN IIn 2010jl, and shows signs of interaction of the SN ejecta with a dense circumstellar medium. High-energy neutrino emission is expected in models of diffusive shock acceleration, but at a low, non-detectable level for this specific SN. In this paper, we describe the SN PTF12csy and present both the neutrino and electromagnetic data, as well as their analysis.

astro-ph.HE↗

arXiv2015

Search for Prompt Neutrino Emission from Gamma-Ray Bursts with IceCube

We present constraints derived from a search of four years of IceCube data for a prompt neutrino flux from gamma-ray bursts (GRBs). A single low-significance neutrino, compatible with the atmospheric neutrino background, was found in coincidence with one of the 506 observed bursts. Although GRBs have been proposed as candidate sources for ultra-high energy cosmic rays, our limits on the neutrino flux disfavor much of the parameter space for the latest models. We also find that no more than $\sim1\%$ of the recently observed astrophysical neutrino flux consists of prompt emission from GRBs that are potentially observable by existing satellites.

astro-ph.HE↗

arXiv2015

Searches for Time Dependent Neutrino Sources with IceCube Data from 2008 to 2012

In this paper searches for flaring astrophysical neutrino sources and sources with periodic emission with the IceCube neutrino telescope are presented. In contrast to time integrated searches, where steady emission is assumed, the analyses presented here look for a time dependent signal of neutrinos using the information from the neutrino arrival times to enhance the discovery potential. A search was performed for correlations between neutrino arrival times and directions as well as neutrino emission following time dependent lightcurves, sporadic emission or periodicities of candidate sources. These include active galactic nuclei, soft $γ$-ray repeaters, supernova remnants hosting pulsars, micro-quasars and X-ray binaries. The work presented here updates and extends previously published results to a longer period that covers four years of data from 2008 April 5 to 2012 May 16 including the first year of operation of the completed 86-string detector. The analyses did not find any significant time dependent point sources of neutrinos and the results were used to set upper limits on the neutrino flux from source candidates.

astro-ph.HE↗

arXiv2015

Determining neutrino oscillation parameters from atmospheric muon neutrino disappearance with three years of IceCube DeepCore data

We present a measurement of neutrino oscillations via atmospheric muon neutrino disappearance with three years of data of the completed IceCube neutrino detector. DeepCore, a region of denser instrumentation, enables the detection and reconstruction of atmospheric muon neutrinos between 10 GeV and 100 GeV, where a strong disappearance signal is expected. The detector volume surrounding DeepCore is used as a veto region to suppress the atmospheric muon background. Neutrino events are selected where the detected Cherenkov photons of the secondary particles minimally scatter, and the neutrino energy and arrival direction are reconstructed. Both variables are used to obtain the neutrino oscillation parameters from the data, with the best fit given by $Δm^2_{32}=2.72^{+0.19}_{-0.20}\times 10^{-3}\,\mathrm{eV}^2$ and $\sin^2θ_{23} = 0.53^{+0.09}_{-0.12}$ (normal mass hierarchy assumed). The results are compatible and comparable in precision to those of dedicated oscillation experiments.

hep-ex↗

arXiv2015

Development of a General Analysis and Unfolding Scheme and its Application to Measure the Energy Spectrum of Atmospheric Neutrinos with IceCube

We present the development and application of a generic analysis scheme for the measurement of neutrino spectra with the IceCube detector. This scheme is based on regularized unfolding, preceded by an event selection which uses a Minimum Redundancy Maximum Relevance algorithm to select the relevant variables and a Random Forest for the classification of events. The analysis has been developed using IceCube data from the 59-string configuration of the detector. 27,771 neutrino candidates were detected in 346 days of livetime. A rejection of 99.9999% of the atmospheric muon background is achieved. The energy spectrum of the atmospheric neutrino flux is obtained using the TRUEE unfolding program. The unfolded spectrum of atmospheric muon neutrinos covers an energy range from 100 GeV to 1 PeV. Compared to the previous measurement using the detector in the 40-string configuration, the analysis presented here, extends the upper end of the atmospheric neutrino spectrum by more than a factor of two, reaching an energy region that has not been previously accessed by spectral measurements.

astro-ph.HE↗

arXiv2015

Flavor Ratio of Astrophysical Neutrinos above 35 TeV in IceCube

A diffuse flux of astrophysical neutrinos above $100\,\mathrm{TeV}$ has been observed at the IceCube Neutrino Observatory. Here we extend this analysis to probe the astrophysical flux down to $35\,\mathrm{TeV}$ and analyze its flavor composition by classifying events as showers or tracks. Taking advantage of lower atmospheric backgrounds for shower-like events, we obtain a shower-biased sample containing 129 showers and 8 tracks collected in three years from 2010 to 2013. We demonstrate consistency with the $(f_e:f_μ:f_τ)_\oplus\approx(1:1:1)_\oplus$ flavor ratio at Earth commonly expected from the averaged oscillations of neutrinos produced by pion decay in distant astrophysical sources. Limits are placed on non-standard flavor compositions that cannot be produced by averaged neutrino oscillations but could arise in exotic physics scenarios. A maximally track-like composition of $(0:1:0)_\oplus$ is excluded at $3.3σ$, and a purely shower-like composition of $(1:0:0)_\oplus$ is excluded at $2.3σ$.

astro-ph.HE↗

arXiv2015

Searches for small-scale anisotropies from neutrino point sources with three years of IceCube data

Recently, IceCube found evidence for a diffuse signal of astrophysical neutrinos in an energy range of $60\,\mathrm{TeV}$ to the $\mathrm{PeV}$-scale. The origin of those events, being a key to understanding the origin of cosmic rays, is still an unsolved question. So far, analyses have not succeeded to resolve the diffuse signal into point-like sources. Searches including a maximum-likelihood-ratio test, based on the reconstructed directions and energies of the detected down- and up-going neutrino candidates, were also performed on IceCube data leading to the exclusion of bright point sources. In this paper, we present two methods to search for faint neutrino point sources in three years of IceCube data, taken between 2008 and 2011. The first method is an autocorrelation test, applied separately to the northern and southern sky. The second method is a multipole analysis, which expands the measured data in the northern hemisphere into spherical harmonics and uses the resulting expansion coefficients to separate signal from background. With both methods, the results are consistent with the background expectation with a slightly more sparse spatial distribution, corresponding to an underfluctuation. Depending on the assumed number of sources, the resulting upper limit on the flux per source in the northern hemisphere for an $E^{-2}$ energy spectrum ranges from $1.5 \cdot 10^{-8}\,\mathrm{GeV}/(\mathrm{cm}^2 \mathrm{s})$, in the case of one assumed source, to $4 \cdot 10^{-10} \,\mathrm{GeV}/(\mathrm{cm}^2 \mathrm{s})$, in the case of $3500$ assumed sources.

astro-ph.HE↗

arXiv2015

Atmospheric and Astrophysical Neutrinos above 1 TeV Interacting in IceCube

The IceCube Neutrino Observatory was designed primarily to search for high-energy (TeV--PeV) neutrinos produced in distant astrophysical objects. A search for $\gtrsim 100$~TeV neutrinos interacting inside the instrumented volume has recently provided evidence for an isotropic flux of such neutrinos. At lower energies, IceCube collects large numbers of neutrinos from the weak decays of mesons in cosmic-ray air showers. Here we present the results of a search for neutrino interactions inside IceCube's instrumented volume between 1~TeV and 1~PeV in 641 days of data taken from 2010--2012, lowering the energy threshold for neutrinos from the southern sky below 10 TeV for the first time, far below the threshold of the previous high-energy analysis. Astrophysical neutrinos remain the dominant component in the southern sky down to 10 TeV. From these data we derive new constraints on the diffuse astrophysical neutrino spectrum, $Φ_ν = 2.06^{+0.4}_{-0.3} \times 10^{-18} \left({E_ν}/{10^5 \,\, \rm{GeV}} \right)^{-2.46 \pm 0.12} {\rm {GeV^{-1} \, cm^{-2} \, sr^{-1} \, s^{-1}} } $, as well as the strongest upper limit yet on the flux of neutrinos from charmed-meson decay in the atmosphere, 1.52 times the benchmark theoretical prediction used in previous IceCube results at 90\% confidence.

astro-ph.HE↗

arXiv2014

IceCube-Gen2: A Vision for the Future of Neutrino Astronomy in Antarctica

The recent observation by the IceCube neutrino observatory of an astrophysical flux of neutrinos represents the "first light" in the nascent field of neutrino astronomy. The observed diffuse neutrino flux seems to suggest a much larger level of hadronic activity in the non-thermal universe than previously thought and suggests a rich discovery potential for a larger neutrino observatory. This document presents a vision for an substantial expansion of the current IceCube detector, IceCube-Gen2, including the aim of instrumenting a $10\,\mathrm{km}^3$ volume of clear glacial ice at the South Pole to deliver substantial increases in the astrophysical neutrino sample for all flavors. A detector of this size would have a rich physics program with the goal to resolve the sources of these astrophysical neutrinos, discover GZK neutrinos, and be a leading observatory in future multi-messenger astronomy programs.

astro-ph.HE↗