| 1. |
- Albert, A., et al.
(författare)
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Discovery of Gamma Rays from the Quiescent Sun with HAWC
- 2023
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 131:5
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Tidskriftsartikel (refereegranskat)abstract
- We report the first detection of a TeV 7-ray flux from the solar disk (6.3a), based on 6.1 years of data from the High Altitude Water Cherenkov (HAWC) observatory. The 0.5-2.6 TeV spectrum is well fit by a power law, dN/dE=A(E/1 TeV)-7, with A = (1.6 & PLUSMN; 0.3) x 10-12 TeV-1 cm-2 s-1 and 7 = 3.62 & PLUSMN; 0.14. The flux shows a strong indication of anticorrelation with solar activity. These results extend the bright, hard GeV emission from the disk observed with Fermi-LAT, seemingly due to hadronic Galactic cosmic rays showering on nuclei in the solar atmosphere. However, current theoretical models are unable to explain the details of how solar magnetic fields shape these interactions. HAWC's TeV detection thus deepens the mysteries of the solar-disk emission.
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| 2. |
- Blanco, Carlos, 1992-, et al.
(författare)
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Where are the Cascades from Blazar Jets? An Emerging Tension in the γ-ray sky
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Blazars are among the most powerful accelerators and are expected to produce a bright TeV γ-ray flux. However, TeV γ-rays are attenuated by interactions with intergalactic radiation before reaching Earth. These interactions produce cascades that transfer TeV power into the GeV band, powering both extended halos around bright sources and a large contribution to the isotropic γ-ray background (IGRB). Using conservative blazar models and recent IGRB measurements, we rule out scenarios where blazars effectively transfer their multi-TeV power into GeV γ-rays. Three possible solutions include: (1) strong spectral cuts on bright blazars, which are increasingly in tension with local blazar data, (2) collective plasma effects that can prevent the development of blazar cascades, the effectiveness of which is debated, (3) an increase in the γ-ray opacity from axion-like particles.
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| 3. |
- Crnogorčević, Milena, et al.
(författare)
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Strong constraints on dark matter annihilation in Ursa Major III/UNIONS 1
- 2024
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Ingår i: Physical Review D. - 2470-0010 .- 2470-0029. ; 109:8
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Tidskriftsartikel (refereegranskat)abstract
- Very recent work has identified a new satellite galaxy, Ursa Major III/UNIONS I, which is the faintest such system ever observed. Dynamical considerations indicate that if the system is in equilibrium, it is likely to be highly dark matter dominated. This, in combination with its proximity, predicts that it may be the preeminent dwarf spheroidal galaxy target for dark matter indirect detection searches. We utilize 15 years of Fermi-LAT data to search for ?-ray emission from Ursa Major III. Finding no excess, we set strong constraints on dark matter annihilation. Intriguingly, if the high J-factor of Ursa Major III is confirmed, standard thermal dark matter annihilation to ?¯? final states would be ruled out for dark matter masses up to 4 TeV. The discovery of Ursa Major III, combined with recent tentative measurements of other high J-factor systems, suggests the exciting possibility that near-future data could produce transformative constraints on thermal dark matter.
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| 4. |
- Delos, M. Sten, et al.
(författare)
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Limits on dark matter annihilation in prompt cusps from the isotropic gamma-ray background
- 2024
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Ingår i: Physical Review D. - 2470-0010 .- 2470-0029. ; 109:8
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Tidskriftsartikel (refereegranskat)abstract
- Recent studies indicate that thermally produced dark matter will form highly concentrated, low-mass cusps in the early universe that often survive until the present. While these cusps contain a small fraction of the dark matter, their high density significantly increases the expected ?-ray flux from dark matter annihilation, particularly in searches of large angular regions. We utilize 14 years of Fermi-LAT data to set strong constraints on dark matter annihilation through a detailed study of the isotropic ?-ray background, excluding with 95% confidence dark matter annihilation to ?¯? final states for dark matter masses below 120 GeV.
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| 5. |
- Evans, Addy J., et al.
(författare)
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On the gamma-ray emission from the core of the Sagittarius dwarf galaxy
- 2023
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Ingår i: Monthly notices of the Royal Astronomical Society. - 0035-8711 .- 1365-2966. ; 524:3, s. 4574-4585
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Tidskriftsartikel (refereegranskat)abstract
- We use Fermi-LAT data to analyse the faint gamma-ray source located at the centre of the Sagittarius (Sgr) dwarf spheroidal galaxy. In the 4FGL-DR3 catalogue, this source is associated with the globular cluster, M54. We investigate the spectral energy distribution and spatial extension of this source, with the goal of testing two hypotheses: (1) the emission is due to millisecond pulsars within M54, or (2) the emission is due to annihilating dark matter from the Sgr halo. For the pulsar interpretation, we consider a two-component model which describes both the lower-energy magnetospheric emission and possible high-energy emission arising from inverse Compton scattering. We find that this source has a point-like morphology at low energies, consistent with magnetospheric emission, and find no evidence for a higher-energy component. For the dark matter interpretation, we find the signal favours a dark matter mass of m(chi)= 29.6 +/- 5.8 GeV and an annihilation cross section of sv = (2. 1 +/- 0.59) x10(-26) cm(3) s(-1) for the b b channel (or m(chi)= 8.3 +/- 3.8 GeV and sv = (0.90 +/- 0.25) x10-26 cm(3) s(-1) for the tau(+) tau(-) channel), when adopting a J -factor of J = 1019.6 GeV2 cm(-5). This parameter space is consistent with gamma-ray constraints from other dwarf galaxies and with dark matter interpretations of the Galactic Centre Gamma-Ray Excess.
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| 6. |
- Jacobsen, Sunniva, et al.
(författare)
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Constraining axion-like particles with HAWC observations of TeV blazars
- 2023
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Ingår i: Journal of Cosmology and Astroparticle Physics. - : IOP Publishing. - 1475-7516. ; 2023:10
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Tidskriftsartikel (refereegranskat)abstract
- Axion-like particles (ALPs) are a broad class of pseudo-scalar bosons that generically arise from broken symmetries in extensions of the standard model. In many scenarios, ALPs can mix with photons in regions with high magnetic fields. Photons from distant sources can mix with ALPs, which then travel unattenuated through the Universe, before they mix back to photons in the Milky Way galactic magnetic field. Thus, photons can traverse regions where their signals would normally be blocked or attenuated. In this paper, we study TeV γ-ray observations from distant blazars, utilizing the significant γ-ray attenuation expected from such signals to look for excess photon fluxes that may be due to ALP-photon mixing. We find no such excesses among a stacked population of seven blazars and constrain the ALP-photon coupling constant to fall below ∼4.5×10-11 GeV-1 for ALP masses below 300 neV. These results are competitive with, or better than, leading terrestrial and astrophysical constraints in this mass range.
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| 7. |
- John, Isabelle, 1994-, et al.
(författare)
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Accurate inverse-Compton models strongly enhance leptophilic dark matter signals
- 2023
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Ingår i: Physical Review D. - 2470-0010 .- 2470-0029. ; 108:10
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Tidskriftsartikel (refereegranskat)abstract
- The annihilation of TeV-scale leptophilic dark matter into electron-positron pairs (hereafter e+e−) will produce a sharp cutoff in the local cosmic-ray e+e− spectrum at an energy matching the dark matter mass. At these high energies, e+e− cool quickly due to synchrotron interactions with magnetic fields and inverse-Compton scattering with the interstellar radiation field. These energy losses are typically modeled as a continuous process. However, inverse-Compton scattering is a stochastic energy-loss process where interactions are rare but catastrophic. We show that when inverse-Compton scattering is modeled as a stochastic process, the expected e+e− flux from dark matter annihilation is about a factor of ∼2 larger near the dark matter mass than in the continuous model. This greatly enhances the detectability of heavy dark matter annihilating to e+e− final states.
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| 8. |
- Keith, Celeste, et al.
(författare)
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Cherenkov Telescope Array will test whether pulsars generate the Galactic Center gamma-ray excess
- 2023
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Ingår i: Physical Review D. - 2470-0010 .- 2470-0029. ; 107:10
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Tidskriftsartikel (refereegranskat)abstract
- The GeV-scale gamma-ray excess observed from the region surrounding the Galactic Center has been interpreted as either the products of annihilating dark matter particles, or as the emission from a large population of faint and centrally located millisecond pulsars. If pulsars are responsible for this signal, then they should also produce detectable levels of TeV-scale emission. In this study, we employ a template-based analysis of simulated data in an effort to assess the ability of the Cherenkov Telescope Array to detect or constrain the presence of this emission, providing a new and powerful means of testing whether millisecond pulsars are responsible for the observed excess. We find that after even a relatively brief observation of the inner galaxy, the Cherenkov Telescope Array will be able to definitively detect this TeV-scale emission, or rule out pulsars as the source of the Galactic Center gamma-ray excess.
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| 9. |
- Leane, Rebecca K., et al.
(författare)
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First Analysis of Jupiter in Gamma Rays and a New Search for Dark Matter
- 2023
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 131:7
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Tidskriftsartikel (refereegranskat)abstract
- We present the first dedicated & gamma;-ray analysis of Jupiter, using 12 years of data from the Fermi Telescope. We find no robust evidence of & gamma;-ray emission, and set upper limits of & SIM;10-9 GeV cm-2 s-1 on the Jovian & gamma;-ray flux. We point out that Jupiter is an advantageous dark matter (DM) target due to its large surface area (compared with other solar system planets), and cool core temperature (compared with the Sun). These properties allow Jupiter to both capture and retain lighter DM, providing a complementary probe of subGeV DM. We therefore identify and perform a new search for DM-sourced & gamma;-rays in Jupiter, where DM annihilates to long-lived particles, which can escape the Jovian surface and decay into & gamma; rays. We consequently constrain DM-proton scattering cross sections as low as about 10-40 cm2, showing Jupiter is up to 10 orders of magnitude more sensitive than direct detection. This sensitivity is reached under the assumption that the mediator decay length is sufficient to escape Jupiter, and the equilibrium between DM capture and annihilation; sensitivities can be lower depending on the DM model. Our work motivates follow-up studies with upcoming MeV telescopes such as AMEGO and e-ASTROGAM.
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| 10. |
- Winkle, Martin, et al.
(författare)
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Cosmic ray antihelium from a strongly coupled dark sector
- 2023
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Ingår i: Physical Review D. - 2470-0010 .- 2470-0029. ; 107:12
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Tidskriftsartikel (refereegranskat)abstract
- Standard Model extensions with a strongly coupled dark sector can induce high-multiplicity states of soft quarks. Such final states trigger extremely efficient antinucleus formation. We show that dark matter annihilation or decay into a strongly coupled sector can dramatically enhance the cosmic-ray antinuclei flux-by six orders of magnitude in the case of 4He. In this work, we argue that the tentative 3He and 4He events reported by the AMS-02 Collaboration could be the first sign of a strongly coupled dark sector observed in nature.
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