lnu.sePublications
Change search
Link to record
Permanent link

Direct link
Alternative names
Publications (10 of 141) Show all publications
Aharonian, F., Benkhali, F. A., Aschersleben, J., Boettcher, M., Backes, M., Martins, V. B., . . . Zywucka, N. (2023). Search for the evaporation of primordial black holes with HESS. Journal of Cosmology and Astroparticle Physics (4), Article ID 040.
Open this publication in new window or tab >>Search for the evaporation of primordial black holes with HESS
Show others...
2023 (English)In: Journal of Cosmology and Astroparticle Physics, E-ISSN 1475-7516, no 4, article id 040Article in journal (Refereed) Published
Abstract [en]

Primordial Black Holes (PBHs) are hypothetical black holes predicted to have been formed from density fluctuations in the early Universe. PBHs with an initial mass around 1014-1015 g are expected to end their evaporation at present times in a burst of particles and very-high-energy (VHE) gamma rays. Those gamma rays may be detectable by the High Energy Stereoscopic System (H.E.S.S.), an array of imaging atmospheric Cherenkov telescopes. This paper reports on the search for evaporation bursts of VHE gamma rays with H.E.S.S., ranging from 10 to 120 seconds, as expected from the final stage of PBH evaporation and using a total of 4816 hours of observations. The most constraining upper limit on the burst rate of local PBHs is 2000 pc-3 yr-1 for a burst interval of 120 seconds, at the 95% confidence level. The implication of these measurements for PBH dark matter are also discussed.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2023
Keywords
gamma ray experiments, primordial black holes, dark matter experiments
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Physics, Astroparticle Physics
Identifiers
urn:nbn:se:lnu:diva-123664 (URN)10.1088/1475-7516/2023/04/040 (DOI)001004513900001 ()2-s2.0-85153538419 (Scopus ID)
Available from: 2023-08-14 Created: 2023-08-14 Last updated: 2023-09-13Bibliographically approved
Aharonian, F., Ashkar, H., Backes, M., Martins, V. B., Becherini, Y., Berge, D., . . . Wong, G. (2022). A deep spectromorphological study of the ϒ-ray emission surrounding the young massive stellar cluster Westerlund 1. Astronomy and Astrophysics, 666, Article ID A124.
Open this publication in new window or tab >>A deep spectromorphological study of the ϒ-ray emission surrounding the young massive stellar cluster Westerlund 1
Show others...
2022 (English)In: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 666, article id A124Article in journal (Refereed) Published
Abstract [en]

Context. Young massive stellar clusters are extreme environments and potentially provide the means for efficient particle acceleration. Indeed, they are increasingly considered as being responsible for a significant fraction of cosmic rays (CRs) that are accelerated within the Milky Way. Westerlund 1, the most massive known young stellar cluster in our Galaxy, is a prime candidate for studying this hypothesis. While the very-high-energy gamma-ray source HESS J1646-458 has been detected in the vicinity of Westerlund 1 in the past, its association could not be firmly identified. Aims. We aim to identify the physical processes responsible for the gamma-ray emission around Westerlund 1 and thus to understand the role of massive stellar clusters in the acceleration of Galactic CRs better. Methods. Using 164 h of data recorded with the High Energy Stereoscopic System (H.E.S.S.), we carried out a deep spectromorphological study of the gamma-ray emission of HESS J1646-458. We furthermore employed H I and CO observations of the region to infer the presence of gas that could serve as target material for interactions of accelerated CRs. Results. We detected large-scale (similar to 2 degrees diameter) gamma-ray emission with a complex morphology, exhibiting a shell-like structure and showing no significant variation with gamma-ray energy. The combined energy spectrum of the emission extends to several tens of TeV, and it is uniform across the entire source region. We did not find a clear correlation of the gamma-ray emission with gas clouds as identified through H I and CO observations. Conclusions. We conclude that, of the known objects within the region, only Westerlund 1 can explain the majority of the gamma-ray emission. Several CR acceleration sites and mechanisms are conceivable and discussed in detail. While it seems clear that Westerlund 1 acts as a powerful particle accelerator, no firm conclusions on the contribution of massive stellar clusters to the flux of Galactic CRs in general can be drawn at this point.

Place, publisher, year, edition, pages
EPD Sciences, 2022
Keywords
acceleration of particles, radiation mechanisms, non-thermal, shock waves, stars, massive, gamma rays, general, galaxies, star clusters, individual, Westerlund 1
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Physics, Astroparticle Physics
Identifiers
urn:nbn:se:lnu:diva-117501 (URN)10.1051/0004-6361/202244323 (DOI)000868825800001 ()2-s2.0-85141010861 (Scopus ID)
Available from: 2022-11-15 Created: 2022-11-15 Last updated: 2022-12-13Bibliographically 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
Show others...
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)
Available from: 2022-09-29 Created: 2022-09-29 Last updated: 2023-01-30Bibliographically 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
Show others...
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
Show others...
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
Abdalla, H., Aharonian, F., Benkhali, F. A., Anguner, E. O., Armand, C., Ashkar, H., . . . Zywucka, N. (2022). Search for Dark Matter Annihilation Signals in the HESS Inner Galaxy Survey. Physical Review Letters, 129(11), Article ID 111101.
Open this publication in new window or tab >>Search for Dark Matter Annihilation Signals in the HESS Inner Galaxy Survey
Show others...
2022 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 129, no 11, article id 111101Article in journal (Refereed) Published
Abstract [en]

The central region of the Milky Way is one of the foremost locations to look for dark matter (DM) signatures. We report the first results on a search for DM particle annihilation signals using new observations from an unprecedented gamma-ray survey of the Galactic Center (GC) region, i.e., the Inner Galaxy Survey, at very high energies (& GSIM;100 GeV) performed with the H.E.S.S. array of five ground-based Cherenkov telescopes. No significant gamma-ray excess is found in the search region of the 2014-2020 dataset and a profile likelihood ratio analysis is carried out to set exclusion limits on the annihilation cross section (sigma v). Assuming Einasto and Navarro-Frenk-White (NFW) DM density profiles at the GC, these constraints are the strongest obtained so far in the TeV DM mass range. For the Einasto profile, the constraints reach (sigma v) values of 3.7 x 10-26 cm3 s-1 for 1.5 TeV DM mass in the W+W- annihilation channel, and 1.2 x 10-26 cm3 s-1 for 0.7 TeV DM mass in the tau+tau- annihilation channel. With the H.E.S.S. Inner Galaxy Survey, ground-based gamma-ray observations thus probe (sigma v) values expected from thermal-relic annihilating TeV DM particles.

Place, publisher, year, edition, pages
American Physical Society, 2022
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Physics, Astroparticle Physics
Identifiers
urn:nbn:se:lnu:diva-117769 (URN)10.1103/PhysRevLett.129.111101 (DOI)000877603700008 ()36154418 (PubMedID)2-s2.0-85138290208 (Scopus ID)
Available from: 2022-12-06 Created: 2022-12-06 Last updated: 2023-03-27Bibliographically 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
Show others...
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
Aharonian, F., Benkhali, F. A., Anguener, E. O., Ashkar, H., Backes, M., Baghmanyan, V., . . . Zywucka, N. (2022). Time-resolved hadronic particle acceleration in the recurrent nova RS Ophiuchi. Science, 376(6588), 77-80
Open this publication in new window or tab >>Time-resolved hadronic particle acceleration in the recurrent nova RS Ophiuchi
Show others...
2022 (English)In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 376, no 6588, p. 77-80Article in journal (Refereed) Published
Abstract [en]

Recurrent novae are repeating thermonuclear explosions in the outer layers of white dwarfs, due to the accretion of fresh material from a binary companion. The shock generated when ejected material slams into the companion star's wind can accelerate particles. We report very-high-energy [VHE: greater than or similar to 100 giga-electron volts] gamma rays from the recurrent nova RS Ophiuchi, up to 1 month after its 2021 outburst, observed using the High Energy Stereoscopic System (H.E.S.S.). The temporal profile of VHE emission is similar to that of lower-energy giga-electron volt emission, indicating a common origin, with a 2-day delay in peak flux. These observations constrain models of time-dependent particle energization, favoring a hadronic emission scenario over the leptonic alternative. Shocks in dense winds provide favorable environments for efficient acceleration of cosmic rays to very high energies.

Place, publisher, year, edition, pages
American Association for Advancement of Science, 2022
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Physics, Astroparticle Physics
Identifiers
urn:nbn:se:lnu:diva-114113 (URN)10.1126/science.abn0567 (DOI)000780195200030 ()35271303 (PubMedID)2-s2.0-85127592016 (Scopus ID)
Available from: 2022-06-15 Created: 2022-06-15 Last updated: 2022-06-28Bibliographically approved
Algaba, J. C., Anczarski, J., Asada, K., Baloković, M., Chandra, S., Cui, Y.-Z. -., . . . Yonekura, Y. (2021). Broadband Multi-wavelength Properties of M87 during the 2017 Event Horizon Telescope Campaign. Astrophysical Journal Letters, 911(1)
Open this publication in new window or tab >>Broadband Multi-wavelength Properties of M87 during the 2017 Event Horizon Telescope Campaign
Show others...
2021 (English)In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 911, no 1Article in journal (Refereed) Published
Abstract [en]

In 2017, the Event Horizon Telescope (EHT) Collaboration succeeded in capturing the first direct image of the center of the M87 galaxy. The asymmetric ring morphology and size are consistent with theoretical expectations for a weakly accreting supermassive black hole of mass ∌6.5 × 109 M o˙. The EHTC also partnered with several international facilities in space and on the ground, to arrange an extensive, quasi-simultaneous multi-wavelength campaign. This Letter presents the results and analysis of this campaign, as well as the multi-wavelength data as a legacy data repository. We captured M87 in a historically low state, and the core flux dominates over HST-1 at high energies, making it possible to combine core flux constraints with the more spatially precise very long baseline interferometry data. We present the most complete simultaneous multi-wavelength spectrum of the active nucleus to date, and discuss the complexity and caveats of combining data from different spatial scales into one broadband spectrum. We apply two heuristic, isotropic leptonic single-zone models to provide insight into the basic source properties, but conclude that a structured jet is necessary to explain M87’s spectrum. We can exclude that the simultaneous γ-ray emission is produced via inverse Compton emission in the same region producing the EHT mm-band emission, and further conclude that the γ-rays can only be produced in the inner jets (inward of HST-1) if there are strongly particle-dominated regions. Direct synchrotron emission from accelerated protons and secondaries cannot yet be excluded. © 2021. The Author(s). Published by the American Astronomical Society..

Place, publisher, year, edition, pages
American Astronomical Society, 2021
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Physics, Astroparticle Physics
Identifiers
urn:nbn:se:lnu:diva-117572 (URN)10.3847/2041-8213/abef71 (DOI)000746900400001 ()2-s2.0-85105584477 (Scopus ID)
Available from: 2022-11-17 Created: 2022-11-17 Last updated: 2023-01-30Bibliographically approved
Abdalla, H., Aharonian, F., Benkhali, F. A., Anguner, E. O., Arcaro, C., Armand, C., . . . Acero, F. (2021). Evidence of 100 TeV gamma-ray emission from HESS J1702-420: A new PeVatron candidate. Astronomy and Astrophysics, 653, Article ID A152.
Open this publication in new window or tab >>Evidence of 100 TeV gamma-ray emission from HESS J1702-420: A new PeVatron candidate