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Aharonian, F., Ait Benkhali, F., Arcaro, C., Aschersleben, J., Backes, M., Barbosa, V. M., . . . Zywucka, N. (2023). Constraining the cosmic-ray pressure in the inner Virgo Cluster using HESS observations of M 87. Astronomy and Astrophysics, 675, Article ID A138.
Open this publication in new window or tab >>Constraining the cosmic-ray pressure in the inner Virgo Cluster using HESS observations of M 87
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2023 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 675, article id A138Article in journal (Refereed) Published
Abstract [en]

The origin of the gamma-ray emission from M 87 is currently a matter of debate. This work aims to localize the very high-energy (VHE; 100 GeV - 100 TeV) gamma-ray emission from M 87 and probe a potential extended hadronic emission component in the inner Virgo Cluster. The search for a steady and extended gamma-ray signal around M 87 can constrain the cosmic-ray energy density and the pressure exerted by the cosmic rays onto the intracluster medium and allow us to investigate the role of cosmic rays in the active galactic nucleus feedback as a heating mechanism in the Virgo Cluster. The High Energy Stereoscopic System (H.E.S.S.) telescopes are sensitive to VHE gamma rays and have been used to observe M 87 since 2004. We utilized a Bayesian block analysis to identify M 87 emission states with H.E.S.S. observations from 2004 to 2021, dividing them into low, intermediate, and high states. Because of the causality argument, an extended (≳1 kpc) signal is allowed only in steady emission states. Hence, we fitted the morphology of the 120 h low-state data and find no significant gamma-ray extension. Therefore, we derive for the low state an upper limit of 58″(corresponding to ≈4.6 kpc) in the extension of a single-component morphological model described by a rotationally symmetric 2D Gaussian model at the 99.7% confidence level. Our results exclude the radio lobes (≈30 kpc) as the principal component of the VHE gamma-ray emission from the low state of M 87. The gamma-ray emission is compatible with a single emission region at the radio core of M 87. These results, with the help of two multiple-component models, constrain the maximum cosmic-ray to thermal pressure ratio to XCR, max. ≲ 0.32 and the total energy in cosmic-ray protons to UCR  ≲  5  ×  1058 erg in the inner 20 kpc of the Virgo Cluster for an assumed cosmic-ray proton power-law distribution in momentum with spectral index αp = 2.1

Place, publisher, year, edition, pages
EDP Sciences, 2023
Keywords
astroparticle physics, gamma rays, galaxies, clusters, intracluster medium, radio continuum
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Physics, Astroparticle Physics
Identifiers
urn:nbn:se:lnu:diva-123893 (URN)10.1051/0004-6361/202346056 (DOI)001033560900005 ()2-s2.0-85165532261 (Scopus ID)
Available from: 2023-08-25 Created: 2023-08-25 Last updated: 2023-09-13Bibliographically approved
Aharonian, F., Aschersleben, J., Backes, M., Martins, V. B., Batzofin, R., Becherini, Y., . . . Zywucka, N. (2023). Constraints on the Intergalactic Magnetic Field Using Fermi-LAT and HESS Blazar Observations. Astrophysical Journal Letters, 950(2), Article ID L16.
Open this publication in new window or tab >>Constraints on the Intergalactic Magnetic Field Using Fermi-LAT and HESS Blazar Observations
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2023 (English)In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 950, no 2, article id L16Article in journal (Refereed) Published
Abstract [en]

Magnetic fields in galaxies and galaxy clusters are believed to be the result of the amplification of intergalactic seed fields during the formation of large-scale structures in the universe. However, the origin, strength, and morphology of this intergalactic magnetic field (IGMF) remain unknown. Lower limits on (or indirect detection of) the IGMF can be obtained from observations of high-energy gamma rays from distant blazars. Gamma rays interact with the extragalactic background light to produce electron-positron pairs, which can subsequently initiate electromagnetic cascades. The gamma-ray signature of the cascade depends on the IGMF since it deflects the pairs. Here we report on a new search for this cascade emission using a combined data set from the Fermi Large Area Telescope and the High Energy Stereoscopic System. Using state-of-the-art Monte Carlo predictions for the cascade signal, our results place a lower limit on the IGMF of B > 7.1 x 10(-16) G for a coherence length of 1 Mpc even when blazar duty cycles as short as 10 yr are assumed. This improves on previous lower limits by a factor of 2. For longer duty cycles of 10(4) (10(7)) yr, IGMF strengths below 1.8 x 10(-14) G (3.9 x 10(-14) G) are excluded, which rules out specific models for IGMF generation in the early universe.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2023
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Physics, Astroparticle Physics
Identifiers
urn:nbn:se:lnu:diva-124085 (URN)10.3847/2041-8213/acd777 (DOI)001021638900001 ()2-s2.0-85164482030 (Scopus ID)
Available from: 2023-09-05 Created: 2023-09-05 Last updated: 2023-10-11Bibliographically approved
Aharonian, F., Benkhali, F. A., Aschersleben, J., Ashkar, H., Backers, M., Martins, V. B., . . . Smith, D. A. (2023). Discovery of a radiation component from the Vela pulsar reaching 20 teraelectronvolts. Nature Astronomy, 7(11), 1341-1350
Open this publication in new window or tab >>Discovery of a radiation component from the Vela pulsar reaching 20 teraelectronvolts
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2023 (English)In: Nature Astronomy, E-ISSN 2397-3366, Vol. 7, no 11, p. 1341-1350Article in journal (Refereed) Published
Abstract [en]

Gamma-ray observations have established energetic isolated pulsars as outstanding particle accelerators and antimatter factories. However, many questions are still open regarding the acceleration and radiation processes involved, as well as the locations where they occur. The radiation spectra of all gamma-ray pulsars observed to date show strong cutoffs or a break above energies of a few gigaelectronvolts. Using the High Energy Stereoscopic System's Cherenkov telescopes, we discovered a radiation component from the Vela pulsar which emerges beyond this generic cutoff and extends up to energies of at least 20 teraelectronvolts. This is an order of magnitude larger than in the case of the Crab pulsar, the only other pulsar detected in the teraelectronvolt energy range. Our results challenge the state-of-the-art models for the high-energy emission of pulsars. Furthermore, they pave the way for investigating other pulsars through their multiteraelectronvolt emission, thereby imposing additional constraints on the acceleration and emission processes in their extreme energy limit. The H.E.S.S. gamma-ray observatory has observed gamma rays with energies of at least 20 TeV from a pulsar, an energy regime that is hard to reconcile with the existing theories of gamma-ray production for such objects.

Place, publisher, year, edition, pages
Nature Publishing Group, 2023
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Physics, Astroparticle Physics
Identifiers
urn:nbn:se:lnu:diva-128517 (URN)10.1038/s41550-023-02052-3 (DOI)001085086100001 ()2-s2.0-85173933154 (Scopus ID)
Note

Correction published in: https://doi.org/10.1038/s41550-023-02151-1.

In the version of the article initially published, R. Zanin, M. Kerr, S. Johnston, R. M. Shannon and D. A. Smith mistakenly appeared in the main author list but are now instead listed as members of The H.E.S.S. Collaboration et al. in the HTML and PDF versions of the article.

Available from: 2024-04-02 Created: 2024-04-02 Last updated: 2024-04-17Bibliographically approved
Aharonian, F., Ait Benkhali, F., Aschersleben, J., Ashkar, H., Backes, M., Barbosa Martins, V., . . . Zywucka, N. (2023). HESS J1809-193: A halo of escaped electrons around a pulsar wind nebula?. Astronomy and Astrophysics, 672, Article ID A103.
Open this publication in new window or tab >>HESS J1809-193: A halo of escaped electrons around a pulsar wind nebula?
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2023 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 672, article id A103Article in journal (Refereed) Published
Abstract [en]

Context. HESS J1809-193 is an unassociated very-high-energy gamma-ray source located on the Galactic plane. While it has been connected to the nebula of the energetic pulsar PSR J1809-1917, supernova remnants and molecular clouds present in the vicinity also constitute possible associations. Recently, the detection of gamma-ray emission up to energies of similar to 100 TeV with the HAWC observatory has led to renewed interest in HESS J1809-193.Aims. We aim to understand the origin of the gamma-ray emission of HESS J1809-193.Methods. We analysed 93.2 h of data taken on HESS J1809-193 above 0.27 TeV with the High Energy Stereoscopic System (H.E.S.S.), using a multi-component, three-dimensional likelihood analysis. In addition, we provide a new analysis of 12.5 yr of Fermi-LAT data above 1 GeV within the region of HESS J1809-193. The obtained results are interpreted in a time-dependent modelling framework.Results. For the first time, we were able to resolve the emission detected with H.E.S.S. into two components: an extended component (modelled as an elongated Gaussian with a 1-sigma semi-major and semi-minor axis of similar to 0.62 degrees and similar to 0.35 degrees, respectively) that exhibits a spectral cutoff at similar to 13 TeV, and a compact component (modelled as a symmetric Gaussian with a 1-sigma radius of similar to 0.1 degrees) that is located close to PSR J1809-1917 and shows no clear spectral cutoff. The Fermi-LAT analysis also revealed extended gamma-ray emission, on scales similar to that of the extended H.E.S.S. component.Conclusions. Our modelling indicates that based on its spectrum and spatial extent, the extended H.E.S.S. component is likely caused by inverse Compton emission from old electrons that form a halo around the pulsar wind nebula. The compact component could be connected to either the pulsar wind nebula or the supernova remnant and molecular clouds. Due to its comparatively steep spectrum, modelling the Fermi-LAT emission together with the H.E.S.S. components is not straightforward.

Place, publisher, year, edition, pages
EDP Sciences, 2023
Keywords
acceleration of particles, radiation mechanisms, non-thermal, pulsars, individual, PSR J1809-1917, gamma rays, general
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Physics, Astroparticle Physics
Identifiers
urn:nbn:se:lnu:diva-120926 (URN)10.1051/0004-6361/202245459 (DOI)000964835500007 ()2-s2.0-85153369428 (Scopus ID)
Available from: 2023-05-26 Created: 2023-05-26 Last updated: 2023-07-03Bibliographically approved
Punch, M., Senniappan, M., Becherini, Y., Kukec Mezek, G., Thoudam, S., Bylund, T. & Ernenwein, J.-P. -. (2023). Sensitivity to point-like sources of the ALTO atmospheric particle detector array, designed for 200GeV-50TeV gamma-ray astronomy. Journal of High Energy Astrophysics, 39, 1-13
Open this publication in new window or tab >>Sensitivity to point-like sources of the ALTO atmospheric particle detector array, designed for 200GeV-50TeV gamma-ray astronomy
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2023 (English)In: Journal of High Energy Astrophysics, ISSN 2214-4048, E-ISSN 2214-4056, Vol. 39, p. 1-13Article in journal (Refereed) Published
Abstract [en]

In the context of atmospheric shower arrays designed for gamma-ray astronomy and in the context of the ALTO project, we present: a study of the impact of heavier nuclei in the cosmic-ray background on the estimated gamma-ray detection performance on the basis of dedicated Monte Carlo simulations, a method to calculate the sensitivity to a point-like source, and finally the required observation times to reach a firm detection on a list of known point-like sources.

Place, publisher, year, edition, pages
Elsevier, 2023
Keywords
Very high-energy gamma-rays, gamma-ray experiments, Extensive air showers, Particle detector arrays, ALTO project, Analysis and statistical methods
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Physics, Astroparticle Physics
Identifiers
urn:nbn:se:lnu:diva-123655 (URN)10.1016/j.jheap.2023.03.003 (DOI)001022243300001 ()2-s2.0-85161678012 (Scopus ID)
Available from: 2023-08-14 Created: 2023-08-14 Last updated: 2023-09-13Bibliographically approved
Aharonian, F., Benkhali, F. A., Anguner, E. O., Ashkar, H., Backes, M., Martins, V. B., . . . Zywucka, N. (2022). Evidence for γ-ray emission from the remnant of Kepler’s supernova based on deep H.E.S.S. observations. Astronomy and Astrophysics, 662, Article ID A65.
Open this publication in new window or tab >>Evidence for γ-ray emission from the remnant of Kepler’s supernova based on deep H.E.S.S. observations
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2022 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 662, article id A65Article in journal (Refereed) Published
Abstract [en]

Observations with imaging atmospheric Cherenkov telescopes (IACTs) have enhanced our knowledge of nearby supernova (SN) remnants with ages younger than 500 yr by establishing Cassiopeia A and the remnant of Tycho's SN as very-high-energy (VHE) gamma-ray sources. The remnant of Kepler's SN, which is the product of the most recent naked-eye SN in our Galaxy, is comparable in age to the other two, but is significantly more distant. If the gamma-ray luminosities of the remnants of Tycho's and Kepler's SNe are similar, then the latter is expected to be one of the faintest gamma-ray sources within reach of the current generation TACT arrays. Here we report evidence at a statistical level of 4.6 sigma for a VHE signal from the remnant of Kepler's SN based on deep observations by the High Energy Stereoscopic System (H.E.S.S.) with an exposure of 152 h. The measured integral flux above an energy of 226 GeV is similar to 0.3% of the flux of the Crab Nebula. The spectral energy distribution (SED) reveals a gamma-ray emitting component connecting the VHE emission observed with H.E.S.S. to the emission observed at GeV energies with Fermi-LAT. The overall SED is similar to that of the remnant of Tycho's SN, possibly indicating the same nonthermal emission processes acting in both these young remnants of thermonuclear SNe.

Place, publisher, year, edition, pages
EDP Sciences, 2022
Keywords
gamma rays: general, supernovae: individual: Kepler, ISM: supernova remnants, radiation mechanisms: non-thermal
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Physics, Astroparticle Physics
Identifiers
urn:nbn:se:lnu:diva-116587 (URN)10.1051/0004-6361/202243096 (DOI)000851302600006 ()2-s2.0-85132576042 (Scopus ID)
Note

Correction published in https://doi.org/10.1051/0004-6361/202348902e 

Available from: 2022-09-29 Created: 2022-09-29 Last updated: 2024-04-12Bibliographically approved
Senniappan, M., Becherini, Y., Punch, M., Thoudam, S., Bylund, T., Kukec Mezek, G. & Ernenwein, J.-P. (2022). Expected performance of the ALTO particle detector array designed for 200 GeV - 50 TeV gamma-ray astronomy. In: Proceedings of Science: 37th International Cosmic Ray Conference (ICRC 2021), July 12th – 23rd, 2021 Online – Berlin, German. Paper presented at 37th International Cosmic Ray Conference (ICRC 2021), July 12th – 23rd, 2021 Online – Berlin, German. Scuola Internazionale Superiore di Studi Avanzati (SISSA), 395, Article ID 761.
Open this publication in new window or tab >>Expected performance of the ALTO particle detector array designed for 200 GeV - 50 TeV gamma-ray astronomy
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2022 (English)In: Proceedings of Science: 37th International Cosmic Ray Conference (ICRC 2021), July 12th – 23rd, 2021 Online – Berlin, German, Scuola Internazionale Superiore di Studi Avanzati (SISSA) , 2022, Vol. 395, article id 761Conference paper, Published paper (Refereed)
Abstract [en]

The ALTO project aims to build a particle detector array for very high energy gamma ray observations optimized for soft spectrum sources. The accurate reconstruction of gamma ray events, in particular their energies, using a surface array is an especially challenging problem at the low energies ALTO aims to optimize for. In this contribution, we leverage Convolutional Neural Networks (CNNs) to improve reconstruction performance at lower energies ( smaller 1 TeV ) as compared to the SEMLA analysis procedure, which is a more traditional method using mainly manually derived features.rnWe present performance figures using different network architectures and training settings, both in terms of accuracy and training time, as well as the impact of various data augmentation techniques.

Place, publisher, year, edition, pages
Scuola Internazionale Superiore di Studi Avanzati (SISSA), 2022
Series
Proceedings of Science (PoS), E-ISSN 1824-8039
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Physics, Astroparticle Physics
Identifiers
urn:nbn:se:lnu:diva-110707 (URN)2-s2.0-85144156458 (Scopus ID)
Conference
37th International Cosmic Ray Conference (ICRC 2021), July 12th – 23rd, 2021 Online – Berlin, German
Available from: 2022-03-04 Created: 2022-03-04 Last updated: 2023-06-28Bibliographically approved
Abe, H., Abe, S., Acciari, V. A., Aniello, T., Ansoldi, S., Antonelli, L. A., . . . Sala, G. (2022). Gamma-ray observations of MAXI J1820+070 during the 2018 outburst. Monthly notices of the Royal Astronomical Society, 517(4), 4736-4751
Open this publication in new window or tab >>Gamma-ray observations of MAXI J1820+070 during the 2018 outburst
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2022 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 517, no 4, p. 4736-4751Article in journal (Refereed) Published
Abstract [en]

MAXIJ1820+070 is a low-mass X-ray binary with a black hole (BH) as a compact object. This binary underwent an exceptionally bright X-ray outburst from 2018 March to October, showing evidence of a non-thermal particle population through its radio emission during this whole period. The combined results of 59.5 h of observations of the MAXI J1820+070 outburst with the H.E.S.S., MAGIC and VERITAS experiments at energies above 200 GeV are presented, together with Fermi-LAT data between 0.1 and 500 GeV, and multiwavelength observations from radio to X-rays. Gamma-ray emission is not detected from MAXI J1820+070, but the obtained upper limits and the multiwavelength data allow us to put meaningful constraints on the source properties under reasonable assumptions regarding the non-thermal particle population and the jet synchrotron spectrum. In particular, it is possible to show that, if a high-energy (HE) gamma-ray emitting region is present during the hard state of the source, its predicted flux should be at most a factor of 20 below the obtained Fermi-LAT upper limits, and closer to them for magnetic fields significantly below equipartition. During the state transitions, under the plausible assumption that electrons are accelerated up to similar to 500 GeV, the multiwavelength data and the gamma-ray upper limits lead consistently to the conclusion that a potential HE and very-HE gamma-ray emitting region should be located at a distance from the BH ranging between 10(11) and 10(13) cm. Similar outbursts from low-mass X-ray binaries might be detectable in the near future with upcoming instruments such as CTA.

Place, publisher, year, edition, pages
Oxford University Press, 2022
Keywords
stars, individual, MAXI J1820+070, gamma rays, general, stars, black holes, X-rays: binaries
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Physics, Astroparticle Physics
Identifiers
urn:nbn:se:lnu:diva-118842 (URN)10.1093/mnras/stac2686 (DOI)000898831500002 ()2-s2.0-85145348890 (Scopus ID)
Available from: 2023-01-30 Created: 2023-01-30 Last updated: 2023-03-27Bibliographically approved
Bylund, T. (2022). Seeking the faint extremes: Detection and characterisation of extragalactic soft-spectrum gamma-ray sources and exploring methods to enhance their detection with machine learning in the 50 GeV-50 TeV energy range. (Doctoral dissertation). Växjö: Linnaeus University Press
Open this publication in new window or tab >>Seeking the faint extremes: Detection and characterisation of extragalactic soft-spectrum gamma-ray sources and exploring methods to enhance their detection with machine learning in the 50 GeV-50 TeV energy range
2022 (English)Doctoral thesis, monograph (Other academic)
Abstract [en]

This thesis deals with an observational study of Blazars, strong gamma-ray sources with Very High Energies (VHE) located far outside our Galaxy. Blazars are a class of galaxies that contain a supermassive black hole that is actively consuming large quantities of matter, a process that results in the liberation of tremendous amounts of energy that then powers the emission of huge bulks of charged particles that get accelerated almost to the speed of light.

The details of the extreme processes involved are still very uncertain, and more observational studies are still required to discriminate between the various theories. Because it takes a lot of energy to create VHE gamma-rays, they are tightly coupled to the most energy-rich places in Blazars.

This means that observations of gamma rays directly probe the central engine responsible for the enormous amounts of radiation we detect.

Direct studies have been carried out with the H.E.S.S. observatory, an Imaging Atmospheric Cherenkov Telescope which uses our atmosphere as an integral part of its detector and is able to detect gamma-ray photons with energies from over 50 GeV up to tens of TeV.

Using H.E.S.S., seven new sources of gamma-rays in the VHE regime were carefully studied in this thesis, significantly expanding the collection of known sources of TeV photons.

Computer studies were also performed exploring the possibility of using deep learning to improve the sensitivity of ALTO, a newly-proposed observatory belonging to an emerging class of gamma-ray instruments, the particle detector arrays.

Place, publisher, year, edition, pages
Växjö: Linnaeus University Press, 2022. p. 203
Series
Linnaeus University Dissertations ; 464
Keywords
GeV gamma-rays, TeV gamma-rays, AGN, blazar, deep learning, observational high-energy astronomy
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Physics, Astroparticle Physics
Identifiers
urn:nbn:se:lnu:diva-116309 (URN)10.15626/LUD.464.2022 (DOI)9789189709379 (ISBN)9789189709386 (ISBN)
Public defence
2022-10-14, Weber (K1009V), Georg Lückligs väg 8, Växjö, 21:42 (English)
Opponent
Supervisors
Available from: 2022-09-23 Created: 2022-09-22 Last updated: 2024-03-07Bibliographically approved
Becherini, Y., Bylund, T., Ernenwein, J.-P., Kukec Mezek, G., Punch, M., Romano, P., . . . Vercellone, S. (2022). The CoMET multiperspective event tracker for wide field-of-view gamma-ray astronomy. In: Proceedings of Science: 37th International Cosmic Ray Conference (ICRC 2021), July 12th – 23rd, 2021 Online – Berlin, German. Paper presented at 37th International Cosmic Ray Conference (ICRC 2021), July 12th – 23rd, 2021, Online – Berlin, German. Scuola Internazionale Superiore di Studi Avanzati (SISSA), 395, Article ID 905.
Open this publication in new window or tab >>The CoMET multiperspective event tracker for wide field-of-view gamma-ray astronomy
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2022 (English)In: Proceedings of Science: 37th International Cosmic Ray Conference (ICRC 2021), July 12th – 23rd, 2021 Online – Berlin, German, Scuola Internazionale Superiore di Studi Avanzati (SISSA) , 2022, Vol. 395, article id 905Conference paper, Published paper (Refereed)
Abstract [en]

The ALTO project aims to build a particle detector array for very high energy gamma ray observations optimized for soft spectrum sources. The accurate reconstruction of gamma ray events, in particular their energies, using a surface array is an especially challenging problem at the low energies ALTO aims to optimize for. In this contribution, we leverage Convolutional Neural Networks (CNNs) to improve reconstruction performance at lower energies ( smaller 1 TeV ) as compared to the SEMLA analysis procedure, which is a more traditional method using mainly manually derived features.rnWe present performance figures using different network architectures and training settings, both in terms of accuracy and training time, as well as the impact of various data augmentation techniques.

Place, publisher, year, edition, pages
Scuola Internazionale Superiore di Studi Avanzati (SISSA), 2022
Series
Proceedings of Science (PoS), E-ISSN 1824-8039
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Physics, Astroparticle Physics
Identifiers
urn:nbn:se:lnu:diva-110708 (URN)2-s2.0-85145018578 (Scopus ID)
Conference
37th International Cosmic Ray Conference (ICRC 2021), July 12th – 23rd, 2021, Online – Berlin, German
Available from: 2022-03-04 Created: 2022-03-04 Last updated: 2023-08-15Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-2946-1313

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