| 1. |
- Bergström, Lars, et al.
(author)
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New Limits on Dark Matter Annihilation from Alpha Magnetic Spectrometer Cosmic Ray Positron Data
- 2013
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In: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 111:17
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Journal article (peer-reviewed)abstract
- The Alpha Magnetic Spectrometer experiment onboard the International Space Station has recently provided cosmic ray electron and positron data with unprecedented precision in the range from 0.5 to 350 GeV. The observed rise in the positron fraction at energies above 10 GeV remains unexplained, with proposed solutions ranging from local pulsars to TeV-scale dark matter. Here, we make use of this high quality data to place stringent limits on dark matter with masses below similar to 300 GeV, annihilating or decaying to leptonic final states, essentially independent of the origin of this rise. We significantly improve on existing constraints, in some cases by up to 2 orders of magnitude.
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| 2. |
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| 3. |
- Cholis, Ilias, et al.
(author)
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Antideuterons and antihelium nuclei from annihilating dark matter
- 2020
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In: Physical Review D. - 2470-0010 .- 2470-0029. ; 102:10
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Journal article (peer-reviewed)abstract
- Recent studies of the cosmic-ray antiproton-to-proton ratio have identified an excess of similar to 10-20 GeV antiprotons relative to the predictions of standard astrophysical models. Intriguingly, the properties of this excess are consistent with the same range of dark matter models that can account for the long-standing excess of gamma-rays observed from the Galactic Center. Such dark matter candidates can also produce significant fluxes of antideuterium and antihelium nuclei. Here we study the production and transport of such particles, both from astrophysical processes as well as from dark matter annihilation. Importantly, in the case of AMS-02, we find that Alfvenic reacceleration (i.e., diffusion in momentum space) can boost the expected number of (d) over bar and 3 (He) over bar events from annihilating dark matter by an order of magnitude or more. For relatively large values of the Alfven speed, and for dark matter candidates that are capable of producing the antiproton and gamma-ray excesses, we expect annihilations to produce a few antideuteron events and about one antihelium event in 6 yr of AMS-02 data. This is particularly interesting in light of recent reports from the AMS-02 Collaboration describing the detection of a number of antihelium candidate events.
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| 4. |
- Cholis, Ilias, et al.
(author)
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Constraining the charge-sign and rigidity-dependence of solar modulation
- 2022
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In: Journal of Cosmology and Astroparticle Physics. - : IOP Publishing. - 1475-7516. ; :10
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Journal article (peer-reviewed)abstract
- Our ability to identify the sources of cosmic rays and understand how these particles propagate through the interstellar medium is hindered by the combined effects of the solar wind and its embedded magnetic field, collectively known as solar modulation. In this paper, we build upon our previous work to model and constrain the effects of solar modulation on the cosmic-ray spectrum, using data from AMS-02 and BESS Polar II collected between 2007 and 2012, during which the heliospheric magnetic field was in a state of negative polarity. Our model uses measurements of the heliospheric magnetic field and the tilt angle of the heliospheric current sheet to accurately predict the effects of solar modulation as a function of time, charge, and rigidity. By incorporating data from a period of negative polarity, we have been able to robustly observe and constrain the charge-dependent effects of solar modulation.
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| 5. |
- Evans, Addy J., et al.
(author)
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On the gamma-ray emission from the core of the Sagittarius dwarf galaxy
- 2023
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In: Monthly notices of the Royal Astronomical Society. - 0035-8711 .- 1365-2966. ; 524:3, s. 4574-4585
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Journal article (peer-reviewed)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. |
- Hooper, Dan, et al.
(author)
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Evidence of TeV halos around millisecond pulsars
- 2022
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In: Physical Review D. - 2470-0010 .- 2470-0029. ; 105:10
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Journal article (peer-reviewed)abstract
- Using data from the HAWC gamma-ray telescope, we have studied a sample of 37 millisecond pulsars (MSPs), selected for their spindown power and proximity. From among these MSP, we have identified four which favor the presence of very high-energy gamma-ray emission at a level of (2ΔlnL)1/2≥2.5. Adopting a correlation between the spindown power and gamma-ray luminosity of each pulsar, we performed a stacked likelihood analysis of these 37 MSPs, finding that the data supports the conclusion that these sources emit very high-energy gamma-rays at a level of (2ΔlnL)1/2=4.24. Among sets of randomly selected sky locations within HAWC’s field-of-view, less than 1% of such realizations yielded such high statistical significance. Our analysis suggests that MSPs produce very high-energy gamma-ray emission with a similar efficiency to that observed from the Geminga TeV-halo, ηMSP=(0.39−1.08)×ηGeminga. This conclusion poses a significant challenge for pulsar interpretations of the Galactic Center gamma-ray excess, as it suggests that any population of MSPs potentially capable of producing the GeV excess would also produce TeV-scale emission in excess of that observed by HESS from this region. Future observations by CTA will be able to substantially clarify this situation.
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| 7. |
- Keith, Celeste, et al.
(author)
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Cherenkov Telescope Array will test whether pulsars generate the Galactic Center gamma-ray excess
- 2023
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In: Physical Review D. - 2470-0010 .- 2470-0029. ; 107:10
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Journal article (peer-reviewed)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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| 8. |
- Keith, Celeste, et al.
(author)
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Sensitivity of future gamma-ray telescopes to primordial black holes
- 2022
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In: Physical Review D. - 2470-0010 .- 2470-0029. ; 106:4
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Journal article (peer-reviewed)abstract
- The strongest existing constraints on primordial black holes with masses in the range of mBH∼1015–1017 g have been derived from measurements of the local cosmic-ray electron-positron flux by Voyager 1, and MeV-scale gamma-ray observations of the inner Galaxy by COMPTEL and INTEGRAL. In this paper, we evaluate the sensitivity of future MeV-scale gamma-ray telescopes such as e-ASTROGAM or AMEGO to Hawking radiation. We show that such an instrument would be able to provide the strongest constraints on black holes in the mass range of mBH∼(0.6–20)×1016 g, typically exceeding current constraints by approximately two orders of magnitude. In scenarios in which the observed 511 keV excess is the result of Hawking radiation, we find that e-ASTROGAM or AMEGO would not only be able to detect the Hawking radiation from the inner Galaxy, but could precisely measure the abundance and mass distribution of the black holes responsible for this signal.
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| 9. |
- Milisavljevic, Dan, et al.
(author)
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MULTI-WAVELENGTH OBSERVATIONS OF SUPERNOVA 2011ei : TIME-DEPENDENT CLASSIFICATION OF TYPE IIb AND Ib SUPERNOVAE AND IMPLICATIONS FOR THEIR PROGENITORS
- 2013
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In: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 767:1, s. 71-
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Journal article (peer-reviewed)abstract
- We present X-ray, UV/optical, and radio observations of the stripped-envelope, core-collapse supernova (SN) 2011ei, one of the least luminous SNe IIb or Ib observed to date. Our observations begin with a discovery within similar to 1 day of explosion and span several months afterward. Early optical spectra exhibit broad, Type II-like hydrogen Balmer profiles that subside rapidly and are replaced by Type Ib-like He-rich features on a timescale of one week. High-cadence monitoring of this transition suggests absorption attributable to a high-velocity (greater than or similar to 12,000 km s(-1)) H-rich shell, which is likely present in many Type Ib events. Radio observations imply a shock velocity of v approximate to 0.13 c and a progenitor star average mass-loss rate of (M) over dot approximate to 1.4 x 10(-5) M-circle dot yr(-1) (assuming wind velocity v(w) = 10(3) km s(-1)). This is consistent with independent constraints from deep X-ray observations with Swift-XRT and Chandra. Overall, the multi-wavelength properties of SN 2011ei are consistent with the explosion of a lower-mass (3-4 M-circle dot), compact (R-* less than or similar to 1 x 10(11) cm), He-core star. The star retained a thin hydrogen envelope at the time of explosion, and was embedded in an inhomogeneous circumstellar wind suggestive of modest episodic mass loss. We conclude that SN 2011ei's rapid spectral metamorphosis is indicative of time-dependent classifications that bias estimates of the relative explosion rates for Type IIb and Ib objects, and that important information about a progenitor star's evolutionary state and mass loss immediately prior to SN explosion can be inferred from timely multi-wavelength observations.
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| 10. |
- Scott, Pat, 1982-
(author)
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Searches for Particle Dark Matter : Dark stars, dark galaxies, dark halos and global supersymmetric fits
- 2010
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Doctoral thesis (other academic/artistic)abstract
- The identity of dark matter is one of the key outstanding problems in both particle and astrophysics. In this thesis, I describe a number of complementary searches for particle dark matter. I discuss how the impact of dark matter on stars can constrain its interaction with nuclei, focussing on main sequence stars close to the Galactic Centre, and on the first stars as seen through the upcoming James Webb Space Telescope. The mass and annihilation cross-section of dark matter particles can be probed with searches for gamma rays produced in astronomical targets. Dwarf galaxies and ultracompact, primordially-produced dark matter minihalos turn out to be especially promising in this respect. I illustrate how the results of these searches can be combined with constraints from accelerators and cosmology to produce a single global fit to all available data. Global fits in supersymmetry turn out to be quite technically demanding, even with the simplest predictive models and the addition of complementary data from a bevy of astronomical and terrestrial experiments; I show how genetic algorithms can help in overcoming these challenges.
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