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Julien Aublin

Publications and source records attributed to Julien Aublin.

10 recordsLinked to original sources
arXiv2025

3C403: a candidate neutrino-emitting radio galaxy

3C403 is a well-known FRII radio galaxy with jets extending up to kiloparsec scales. We report its identification as the second most significant candidate among more than 150 sources examined using the 15-year neutrino dataset from the ANTARES Collaboration, making it one of the most promising radio-galaxy candidates for high-energy neutrino emission. Motivated by previous associations between blazars and neutrino events, we investigated the jet properties of 3C403 and their possible role in neutrino production. Multi-scale radio observations, from parsec to kiloparsec scales, reveal a stable, two-sided jet lying close to the plane of the sky, with no evidence of strong Doppler boosting, while X-ray data indicate a dominant, heavily absorbed accretion-related component. We also examined the recently proposed correlation between neutrino and hard X-ray fluxes - originally identified in blazars and Seyfert galaxies - and find that 3C403 occupies an intermediate location in the $L_{\nu}$--$L_{\rm hX}$ plane between jet-dominated and corona-dominated systems. However, the current upper limit on its neutrino flux prevents a firm assessment of whether it follows the proposed relation. With radiatively efficient accretion ($\lambda_{\rm Edd}\sim10^{-2}$), strong hard X-ray emission, and a powerful but misaligned jet, 3C403 provides a physically motivated laboratory for exploring the interplay between coronal activity and jet environments in multimessenger scenarios of neutrino production in active galaxies.

astro-ph.HE↗
arXiv2023

What can be learnt from UHECR anisotropies observations Paper II: intermediate-scale anisotropies

Analysing the available data relative to the anisotropies of the ultra-high-energy cosmic rays (UHECR) at intermediate angular scales, we examine to what extent they can be used to constrain the origin of these particles, and what could be gained from a new generation of observatories with increased exposure. We simulate realistic UHECR sky maps for a wide range of scenarios, with the assumption that the distribution of UHECR sources follows that of matter in the Universe, also considering possible biases. We produce numerous datasets on which we apply similar analyses as those recently used by the Auger and TA collaborations. We find that: i) the investigated scenarios can easily account for the significance of the anisotropies reported by Auger and TA; ii) the direction in which the maximum flux excess is found in the Auger data differs from where it is found in most of our simulations; iii) for datasets simulated with the same astrophysical scenario, the significance with which the isotropy hypothesis is rejected through the Auger likelihood analysis can be largest either when "all galaxies" or when "starburst" galaxies are used to model the signal, depending on which GMF model is used; iv) the study of the energy evolution of the anisotropy patterns can provide new insight about the origin of UHECRs; v) the direction in which the most significant flux excess is found in the Auger dataset above 8 EeV appears to essentially disappear in the dataset above 32 EeV; vi) this appears to be very uncommon in our simulations, which could point to a failure of some generic assumption in the investigated scenarios, such as the predominance of a unique type of sources in the flux above the ankle, with essentially the same composition and spectrum; vii) a meaningful measurement of their energy evolution, from 10 EeV to the highest energies, will require a significant increase in statistics.

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arXiv2020

Event reconstruction for KM3NeT/ORCA using convolutional neural networks

The KM3NeT research infrastructure is currently under construction at two locations in the Mediterranean Sea. The KM3NeT/ORCA water-Cherenkov neutrino detector off the French coast will instrument several megatons of seawater with photosensors. Its main objective is the determination of the neutrino mass ordering. This work aims at demonstrating the general applicability of deep convolutional neural networks to neutrino telescopes, using simulated datasets for the KM3NeT/ORCA detector as an example. To this end, the networks are employed to achieve reconstruction and classification tasks that constitute an alternative to the analysis pipeline presented for KM3NeT/ORCA in the KM3NeT Letter of Intent. They are used to infer event reconstruction estimates for the energy, the direction, and the interaction point of incident neutrinos. The spatial distribution of Cherenkov light generated by charged particles induced in neutrino interactions is classified as shower- or track-like, and the main background processes associated with the detection of atmospheric neutrinos are recognized. Performance comparisons to machine-learning classification and maximum-likelihood reconstruction algorithms previously developed for KM3NeT/ORCA are provided. It is shown that this application of deep convolutional neural networks to simulated datasets for a large-volume neutrino telescope yields competitive reconstruction results and performance improvements with respect to classical approaches.

astro-ph.IM↗
arXiv2020

gSeaGen: the KM3NeT GENIE-based code for neutrino telescopes

The gSeaGen code is a GENIE-based application developed to efficiently generate high statistics samples of events, induced by neutrino interactions, detectable in a neutrino telescope. The gSeaGen code is able to generate events induced by all neutrino flavours, considering topological differences between track-type and shower-like events. Neutrino interactions are simulated taking into account the density and the composition of the media surrounding the detector. The main features of gSeaGen are presented together with some examples of its application within the KM3NeT project.

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arXiv2019

Searches for point-like sources of cosmic neutrinos with 11 years of ANTARES data

The main goal of the ANTARES neutrino telescope is the identification of neutrinos from cosmic accelerators. The good visibility towards the Southern sky for neutrino energies below 100 TeV and the good angular resolution for reconstructed events make the telescope excellent to test for the presence of point-like sources, especially of Galactic origin. The median angular resolution for track-like events (mainly from $ν_μ$ CC interactions) is $0.4^{\circ}$ while the median angular resolution for contained shower-like events (mainly from $ν_{e}$ CC and all-flavour NC interactions) is $3^{\circ}$. Recently the ANTARES Collaboration published the result of the search for cosmic point-like neutrino sources using track-like and shower-like events collected during nine years of data taking. In this contribution, an update to this analysis using eleven years of data recorded between early 2007 and the end of 2017, for a total livetime of 3136 days, is presented. Moreover, the results of a search for time and space correlation between the ANTARES events and 54 IceCube tracks and those of the searches for neutrino candidates associated with the IceCube-170922A event or from the direction of the TXS 0506+056 blazar are reported.

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arXiv2016

Measurement of the Radiation Energy in the Radio Signal of Extensive Air Showers as a Universal Estimator of Cosmic-Ray Energy

We measure the energy emitted by extensive air showers in the form of radio emission in the frequency range from 30 to 80 MHz. Exploiting the accurate energy scale of the Pierre Auger Observatory, we obtain a radiation energy of 15.8 \pm 0.7 (stat) \pm 6.7 (sys) MeV for cosmic rays with an energy of 1 EeV arriving perpendicularly to a geomagnetic field of 0.24 G, scaling quadratically with the cosmic-ray energy. A comparison with predictions from state-of-the-art first-principle calculations shows agreement with our measurement. The radiation energy provides direct access to the calorimetric energy in the electromagnetic cascade of extensive air showers. Comparison with our result thus allows the direct calibration of any cosmic-ray radio detector against the well-established energy scale of the Pierre Auger Observatory.

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arXiv2016

Energy Estimation of Cosmic Rays with the Engineering Radio Array of the Pierre Auger Observatory

The Auger Engineering Radio Array (AERA) is part of the Pierre Auger Observatory and is used to detect the radio emission of cosmic-ray air showers. These observations are compared to the data of the surface detector stations of the Observatory, which provide well-calibrated information on the cosmic-ray energies and arrival directions. The response of the radio stations in the 30 to 80 MHz regime has been thoroughly calibrated to enable the reconstruction of the incoming electric field. For the latter, the energy deposit per area is determined from the radio pulses at each observer position and is interpolated using a two-dimensional function that takes into account signal asymmetries due to interference between the geomagnetic and charge-excess emission components. The spatial integral over the signal distribution gives a direct measurement of the energy transferred from the primary cosmic ray into radio emission in the AERA frequency range. We measure 15.8 MeV of radiation energy for a 1 EeV air shower arriving perpendicularly to the geomagnetic field. This radiation energy -- corrected for geometrical effects -- is used as a cosmic-ray energy estimator. Performing an absolute energy calibration against the surface-detector information, we observe that this radio-energy estimator scales quadratically with the cosmic-ray energy as expected for coherent emission. We find an energy resolution of the radio reconstruction of 22% for the data set and 17% for a high-quality subset containing only events with at least five radio stations with signal.

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arXiv2015

Measurement of the cosmic ray spectrum above $4{\times}10^{18}$ eV using inclined events detected with the Pierre Auger Observatory

A measurement of the cosmic-ray spectrum for energies exceeding $4{\times}10^{18}$ eV is presented, which is based on the analysis of showers with zenith angles greater than $60^{\circ}$ detected with the Pierre Auger Observatory between 1 January 2004 and 31 December 2013. The measured spectrum confirms a flux suppression at the highest energies. Above $5.3{\times}10^{18}$ eV, the "ankle", the flux can be described by a power law $E^{-γ}$ with index $γ=2.70 \pm 0.02 \,\text{(stat)} \pm 0.1\,\text{(sys)}$ followed by a smooth suppression region. For the energy ($E_\text{s}$) at which the spectral flux has fallen to one-half of its extrapolated value in the absence of suppression, we find $E_\text{s}=(5.12\pm0.25\,\text{(stat)}^{+1.0}_{-1.2}\,\text{(sys)}){\times}10^{19}$ eV.

astro-ph.HE↗
arXiv2015

An improved limit to the diffuse flux of ultra-high energy neutrinos from the Pierre Auger Observatory

Neutrinos in the cosmic ray flux with energies near 1 EeV and above are detectable with the Surface Detector array of the Pierre Auger Observatory. We report here on searches through Auger data from 1 January 2004 until 20 June 2013. No neutrino candidates were found, yielding a limit to the diffuse flux of ultra-high energy neutrinos that challenges the Waxman-Bahcall bound predictions. Neutrino identification is attempted using the broad time-structure of the signals expected in the SD stations, and is efficiently done for neutrinos of all flavors interacting in the atmosphere at large zenith angles, as well as for "Earth-skimming" neutrino interactions in the case of tau neutrinos. In this paper the searches for downward-going neutrinos in the zenith angle bins $60^\circ-75^\circ$ and $75^\circ-90^\circ$ as well as for upward-going neutrinos, are combined to give a single limit. The $90\%$ C.L. single-flavor limit to the diffuse flux of ultra-high energy neutrinos with an $E^{-2}$ spectrum in the energy range $1.0 \times 10^{17}$ eV - $2.5 \times 10^{19}$ eV is $E_ν^2 dN_ν/dE_ν< 6.4 \times 10^{-9}~ {\rm GeV~ cm^{-2}~ s^{-1}~ sr^{-1}}$.

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