arXiv subjects

Bruno Arsioli

Publications and source records attributed to Bruno Arsioli.

9 recordsLinked to original sources

arXiv2026

The Road to Identifying the Earliest Radio-Powerful AGN with the SKA

The Epoch of Reionization (EoR) is one of the most pivotal frontiers in modern astrophysics, marking the emergence of the first galaxies, stars, and supermassive black holes (SMBHs). Despite insights from the Atacama Large Millimetre/submillimetre Array and the James Webb Space Telescope, we still struggle to explain how $\sim10^{9}$ M$_\odot$ SMBHs powering luminous active galactic nuclei (AGN) already exist by $z\sim7$. The recent discovery of powerful radio emission from some of these early AGN is notable, offering new constraints on early black-hole accretion and, with the Square Kilometre Array Observatory (SKAO), the prospect of directly probing neutral hydrogen through 21-cm absorption studies. Yet progress remains slow: only a few radio-powerful AGN are known at $z>6$, far fewer than theoretical predictions suggest, raising questions about whether this reflects intrinsic properties or selection biases and incomplete spectral information. In this chapter we synthesise predictions from state-of-the-art hydrodynamical and semi-analytic simulations with observational constraints from SKAO pathfinder facilities. These models suggest the existence of a substantial, still-undetected population of radio-powerful AGN in the EoR, but show that present surveys are limited by selection biases and incomplete radio spectral information. We discuss a physically motivated strategy for identifying high-redshift radio AGN, based on broadband radio spectral energy distributions, spectral curvature, dynamical jet evolution, and radio-only redshift estimation, offering a transformative alternative to traditional empirical approaches. Finally, we justify how the sensitivity and spectral coverage of the SKAO will allow fine-frequency sampling across the 50 MHz - 15 GHz range, revolutionising our ability to identify the earliest radio-powerful AGN and probe the earliest SMBHs.

astro-ph.GA↗

arXiv2024

Mapping the Cosmic Gamma-ray Horizon: The 1CGH Catalogue of Fermi-LAT detections above 10 GeV

We present the First Cosmic Gamma-ray Horizon (1CGH) catalogue, featuring $\gamma$-ray detections above 10 GeV based on 16 years of observations with the Fermi Large Area Telescope (LAT) satellite. After carefully selecting a sample of blazars and blazar candidates from catalogues in the literature, we performed a binned likelihood analysis and identified 2791 $\gamma$-ray emitters above 10 GeV, at >3$\sigma$ level, including 62 that are new $\gamma$-ray detections. For each source, we estimated the mean energy of the highest-energy bin and analysed them in the context of the cosmic gamma-ray horizon. By adopting a reference model for the Extragalactic Background Light (EBL), we identified a subsample of 525 sources where moderate to severe $\gamma$-ray absorption could be detected across the redshift range of 0 to 3. This work provides the most up-to-date compilation of detections above 10 GeV, along with their redshift information. We condense extensive results from the literature, including reports on observational campaigns dedicated to blazars and $\gamma$-ray sources, thereby delivering an unprecedented review of the redshift information for sources detected above 10 GeV. Additionally, we highlight key 1CGH sources where redshift information remains incomplete, offering guidance for future optical observation campaigns. The 1CGH catalogue aims to track the most significant sources for studying the $\gamma$-ray transparency of the Universe. Furthermore, it provides a targeted subsample where the EBL optical depth, $\tau_{(E,z)}$, can be robustly measured using Fermi-LAT data.

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arXiv2024

Yet Another Sunshine Mystery: Unexpected Asymmetry in GeV Emission from the Solar Disk

The Sun is one of the most luminous $γ$-ray sources in the sky and continues to challenge our understanding of its high-energy emission mechanisms. This study provides an in-depth investigation of the solar disk $γ$-ray emission, using data from the Fermi Large Area Telescope spanning 2008 August to 2022 January. We focus on $γ$-ray events with energies exceeding 5 GeV, originating from 0.5$^\circ$ angular aperture centered on the Sun, and implement stringent time cuts to minimize potential sample contaminants. We use a helioprojection method to resolve the $γ$-ray events relative to the solar rotation axes and combine statistical tests to investigate the distribution of events over the solar disk. We found that integrating observations over large time windows may overlook relevant asymmetrical features, which we reveal in this work through a refined time-dependent morphological analysis. We describe significant anisotropic trends and confirm compelling evidence of energy-dependent asymmetry in the solar disk $γ$-ray emission. Intriguingly, the asymmetric signature coincides with the Sun's polar field flip during the cycle 24 solar maximum, around 2014 June. Our findings suggest that the Sun's magnetic configuration plays a significant role in shaping the resulting $γ$-ray signature, highlighting a potential link between the observed anisotropies, solar cycle, and the solar magnetic fields. These insights pose substantial challenges to established emission models, prompting fresh perspectives on high-energy solar astrophysics.

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arXiv2022

Hunting for neutrino emission from multi-frequency variable sources

Pinpointing the neutrino sources is crucial to unveil the mystery of high-energy cosmic rays. The search for neutrino-source candidates from coincident neutrino-photon signatures and electromagnetic objects with peculiar flaring behaviors have the potential to increase our chances of finding neutrino emitters. In this paper, we first study the temporal correlations of astrophysical flares with neutrinos, considering a few hundreds of multi-frequency sources from ALMA, WISE, Swift, and Fermi in the containment regions of IceCube high-energy alerts. Furthermore, the spatial correlations between blazars and neutrinos are investigated using the subset of 10-year IceCube track-like neutrinos with around 250 thousand events. In the second test, we account for 2700 blazars with different types of flaring phases in addition to sole position. No significant neutrino emissions were found from our analyses. Our results indicate an interesting trend showing the infrared flaring stages of WISE blazars might be correlated with arrival times of the neutrino alerts. Possible overflow of neutrinos associated with two of our blazar sub-samples are also illustrated. One is characterized by a significant flaring lag in infrared with respect to gamma-rays, like seen for TXS0506+056, and the other is characterized by highly simultaneous infrared and gamma-ray flares. These phenomena suggest the need to improve current multi-frequency light-curve catalogs to pair with the advent of more sensitive neutrino observatories.

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arXiv2020

Machine Learning applied to Multifrequency Data in Astrophysics: Blazar Classification

The study of machine learning (ML) techniques for the autonomous classification of astrophysical sources is of great interest, and we explore its applications in the context of a multifrequency data-frame. We test the use of supervised ML to classify blazars according to its synchrotron peak frequency, either lower or higher than 10$^{15}$Hz. We select a sample with 4178 blazars labelled as 1279 high synchrotron peak (HSP: $\rm ν$-peak > 10$^{15}$Hz) and 2899 low synchrotron peak (LSP: $\rm ν$-peak < 10$^{15}$Hz). A set of multifrequency features were defined to represent each source, that includes spectral slopes ($α_{ν_1, ν_2}$) between the radio, infra-red, optical, and X-ray bands, also considering IR colours. We describe the optimisation of five ML classification algorithms that classify blazars into LSP or HSP: Random Forests (RF), Support Vector Machine (SVM), K-Nearest Neighbours (KNN), Gaussian Naive Bayes (GNB) and the Ludwig auto-ML framework. In our particular case, the SVM algorithm had the best performance, reaching 93% of balanced-accuracy. A joint-feature permutation test revealed that the spectral slopes alpha-radio-IR and alpha-radio-optical are the most relevant for the ML modelling, followed by the IR colours. This work shows that ML algorithms can distinguish multifrequency spectral characteristics and handle the classification of blazars into LSPs and HSPs. It is a hint for the potential use of ML for the autonomous determination of broadband spectral parameters (as the synchrotron $ν$-peak), or even to search for new blazars in all-sky databases.

astro-ph.HE↗

arXiv2020

Extreme & High Synchrotron Peak Blazars beyond 4FGL: The 2BIGB $\rm γ$-ray catalogue

This paper presents the results of a $\rm γ$-ray likelihood analysis over all the extreme and high synchrotron peak blazars (EHSP & HSP) from the 3HSP catalogue. We investigate 2013 multifrequency positions under the eyes of Fermi Large Area Telescope, considering 11 years of observations in the energy range between 500 MeV to 500 GeV, which results in 1160 $\rm γ$-ray signatures detected down to the TS = 9 threshold. The detections include 235 additional sources concerning the Fermi Large Area Telescope Fourth Source Catalog (4FGL), all confirmed via high-energy TS maps, and represent an improvement of ~25% for the number of EHSP & HSP currently described in $\rm γ$-rays. We build the $\rm γ$-ray spectral energy distribution for all the 1160 2BIGB sources, plot the corresponding $\rm γ$-ray logN-logS, and measure their total contribution to the extragalactic gamma-ray background, which reaches up to ~33% at 100 GeV. Also, we show that the $\rm γ$-ray detectability improves according to the synchrotron peak flux as represented by the Figure of Merit (FOM) parameter, and note that the search for TeV peaked blazars may benefit from considering HSP and EHSP as a whole, instead of EHSPs only. The 2BIGB acronym stands for `Second Brazil-ICRANet Gamma-ray Blazars' catalogue, and all the broadband models and spectral energy distribution data-points will be available on public data repositories (OpenUniverse, GitHub, and Brazilian Science Data Center-BSDC)

astro-ph.HE↗

arXiv2019

The 3HSP catalogue of Extreme & High Synchrotron Peaked Blazars

High synchrotron peaked blazars (HSPs or HBLs) play a central role in very high energy (VHE) gamma-ray astronomy, and likely in neutrino astronomy. Currently, the largest compilation of HSP blazars, the 2WHSP sample, includes 1691 sources, but it is not complete neither in the radio nor in the X-ray band. In order to provide a more sizable and more accurate set of HSP blazars that is useful for future statistical studies and to plan for VHE/TeV observations, we present the largest sample of extreme and high synchrotron peaked (EHSP;HSP) blazars and blazar candidates: the 3HSP catalogue. The 3HSP catalogue includes 2013 sources, 88% of which with a redshift estimation, a much larger percentage than in any other list of HSP blazars. All new γ-ray detections are described in the First and Second Brazil ICRANet gamma-ray blazar catalogues (1BIGB & 2BIGB) also taking into account the 4FGL list of γ-ray sources published by the Fermi large area telescope (Fermi-LAT) team. Moreover, the cross-matching between the 2WHSP, 2FHL HSPs, and IceCube neutrinos position has suggested that HSPs are likely counterparts of neutrino events, which implies the 3HSP catalogue is useful also in that respect. The 3HSP catalogue features improved completeness compared to its predecessors, the 1WHSP and 2WHSP catalogues, and follows the track of their increasing relevance for VHE astronomy.

astro-ph.HE↗

arXiv2016

Searching for $γ$-ray signature in WHSP blazars: Fermi-LAT detection of 150 excess signal in the 0.3-500 GeV band

A direct search of $γ$-ray emission centered on multi-frequency selected candidates is a valuable complementary approach to the standard search adopted in current $γ$-ray Fermi-LAT catalogs. Our candidates are part of the 2WHSP sample, that was assembled with the aim of providing targets for Imaging Atmospheric Cherenkov Telescopes (IACT), and is currently the largest set of high synchrotron peaked (HSP) blazars. We perform a likelihood analysis with the Fermi Science Tools using positions from 400 2WHSP blazars as seeds of tentative $γ$-ray sources. This enabled us to detect 150 $γ$-ray excess signals that have not yet been reported in previous $γ$-ray catalogs (1FGL, 2FGL, and 3FGL). By identifying new sources, we solve a fraction of the extragalactic isotropic $γ$-ray background (IGRB) composition, improving the description of the $γ$-ray sky. Our analysis considers the 0.3-500 GeV energy band, integrating over 7.2 yrs of Fermi-LAT observation and making use of the Pass 8 data release. Within the 150 2WHSPs that showed excess $γ$-ray signature: 85 are high-significance detections with test statistic (TS)$>$25, and 65 are lower-significance detections with TS between 10 to 25. We study the $γ$-ray photon spectral index distribution, the likelihood of detection according to the synchrotron peak brightness, and plot the measured $γ$-ray LogN-LogS of HSP blazars, also discussing the portion of the IGRB that has been resolved by this work. We report on four cases where we could resolve source confusion and find counterparts for unassociated 3FGL sources with the help of high-energy TS maps together with multi-frequency data. The 150 new $γ$-ray sources are named with the acronym 1BIGB for the first version of the Brazil ICRANet Gamma-ray Blazar catalog, in reference to the cooperation agreement supporting this work.

astro-ph.HE↗

arXiv2016

2WHSP: A catalog of HE and VHE gamma-ray blazars and blazar candidates

Aims. High Synchrotron Peaked blazars (HSPs) dominate the -ray sky at energies larger than a few GeV; however, only a few hundred blazars of this type have been catalogued so far. In this paper we present the 2WHSP sample, the largest and most complete list of HSP blazars available to date, which is an expansion of the 1WHSP catalog of gamma-ray source candidates off the Galactic plane. Methods. We cross-matched a number of multi-wavelength surveys (in the radio, infrared and X-ray bands) and applied selection criteria based on the radio to IR and IR to X-ray spectral slopes. To ensure the selection of genuine HSPs we examined the SED of each candidate and estimated the peak frequency of its synchrotron emission ($ν_{\rm peak}$) using the ASDC SED tool, including only sources with Synchrotron peak $ν_{\rm peak} > 10^{15}$ Hz (equivalent to $ν_{\rm peak} > 4$ eV). Results. We have assembled the largest and most complete catalog of HSP blazars to date, which includes 1691 sources. A number of population properties, such as infrared colours, synchrotron peak, redshift distributions, and -ray spectral properties, have been used to characterise the sample and maximize completeness. We also derived the radio logN-logS distribution. This catalog has already been used to provide seeds to discover new very high energy objects within Fermi-LAT data and to look for the counterparts of neutrino and ultra high energy cosmic ray sources, showing its potential for the identification of promising high-energy gamma-ray sources and multi-messenger targets.

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