| 1. |
- Bringmann, Torsten, et al.
(författare)
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Dark Matter signals from Draco and Willman 1 : Prospects for MAGIC II and CTA
- 2009
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Ingår i: Journal of Cosmology and Astroparticle Physics. - 1475-7516. ; 01:016
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Tidskriftsartikel (refereegranskat)abstract
- The next generation of ground-based Imaging Air Cherenkov Telescopes (IACTs) will play an important role in indirect dark matter searches. In this article, we consider two particularly promising candidate sources for dark matter annihilation signals, the nearby dwarf galaxies Draco and Willman 1, and study the prospects of detecting such a signal for the soon-operating MAGIC II telescope system as well as for the planned installation of CTA, taking special care of describing the experimental features that affect the detectional prospects. For the first time in such a study, we fully take into account the effect of internal bremsstrahlung, which has recently been shown to considerably enhance, in some cases, the gamma-ray flux at the high energies where Atmospheric Cherenkov Telescopes operate, thus leading to significantly harder annihilation spectra than traditionally considered. While the detection of the spectral features introduced by internal bremsstrahlung would constitute a smoking gun signature for dark matter annihilation, we find that for most models the overall flux still remains at a level that will be challenging to detect unless one adopts rather (though by no means overly) optimistic astrophysical assumptions about the distribution of dark matter in the dwarfs
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| 2. |
- Fornasa, Mattia, et al.
(författare)
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Angular power spectrum of the diffuse gamma-ray emission as measured by the Fermi Large Area Telescope and constraints on its dark matter interpretation
- 2016
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Ingår i: Physical Review D. - 2470-0010. ; 94:12
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Tidskriftsartikel (refereegranskat)abstract
- The isotropic gamma-ray background arises from the contribution of unresolved sources, including members of confirmed source classes and proposed gamma-ray emitters such as the radiation induced by dark matter annihilation and decay. Clues about the properties of the contributing sources are imprinted in the anisotropy characteristics of the gamma-ray background. We use 81 months of Pass 7 Reprocessed data from the Fermi Large Area Telescope to perform a measurement of the anisotropy angular power spectrum of the gamma-ray background. We analyze energies between 0.5 and 500 GeV, extending the range considered in the previous measurement based on 22 months of data. We also compute, for the first time, the cross-correlation angular power spectrum between different energy bins. We find that the derived angular spectra are compatible with being Poissonian, i.e. constant in multipole. Moreover, the energy dependence of the anisotropy suggests that the signal is due to two populations of sources, contributing, respectively, below and above similar to 2 GeV. Finally, using data from state-of-the-art numerical simulations to model the dark matter distribution, we constrain the contribution from dark matter annihilation and decay in Galactic and extra-Galactic structures to the measured anisotropy. These constraints are competitive with those that can be derived from the average intensity of the isotropic gamma-ray background.
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| 3. |
- Fornasa, Mattia, et al.
(författare)
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The nature of the Diffuse Gamma-Ray Background
- 2015
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Ingår i: Physics reports. - : Elsevier BV. - 0370-1573 .- 1873-6270. ; 598, s. 1-58
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Forskningsöversikt (refereegranskat)abstract
- We review the current understanding of the Diffuse Gamma-Ray Background (DGRB). The DGRB is what remains of the total measured gamma-ray emission after the subtraction of the resolved sources and of the diffuse Galactic foregrounds. It is interpreted as the cumulative emission of sources that are not bright enough to be detected individually. Yet, its exact composition remains unveiled. Well-established astrophysical source populations (e.g. blazars, misaligned AGNs, star-forming galaxies and millisecond pulsars) all represent guaranteed contributors to the DGRB. More exotic scenarios, such as Dark Matter annihilation or decay, may contribute as well. In this review, we describe how these components have been modeled in the literature and how the DGRB can be used to provide valuable information on each of them. We summarize the observational information currently available on the DGRB, paying particular attention to the most recent measurement of its intensity energy spectrum by the Fermi LAT Collaboration. We also discuss the novel analyses of the auto-correlation angular power spectrum of the DGRB and of its cross-correlation with tracers of the large-scale structure of the Universe. New data sets already (or soon) available are expected to provide further insight on the nature of this emission. By summarizing where we stand on the current knowledge of the DGRB, this review is intended both as a useful reference for those interested in the topic and as a means to trigger new ideas for further research.
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| 4. |
- Xia, Jun-Qing, et al.
(författare)
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A cross-correlation study of the Fermi-LAT gamma-ray diffuse extragalactic signal
- 2011
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 416:3, s. 2247-2264
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Tidskriftsartikel (refereegranskat)abstract
- In this work, starting from 21 months of data from the Fermi Large Area Telescope (LAT), we derive maps of the residual isotropic gamma-ray emission, a relevant fraction of which is expected to be contributed by the extragalactic diffuse gamma-ray background (EGB). We search for the auto-correlation signals in the above gamma-ray maps and for the cross-correlation signal with the angular distribution of different classes of objects that trace the large-scale structure of the Universe. We compute the angular two-point auto-correlation function of the residual Fermi-LAT maps at energies E > 1 GeV, E > 3 GeV and E > 30 GeV well above the Galactic plane and find no significant correlation signal. This is, indeed, what is expected if the EGB were contributed by BL Lacertae (BLLacs), Flat Spectrum Radio Quasars (FSRQs) or star-forming galaxies, since, in this case, the predicted signal is very weak. Then, we search for the Integrated Sachs-Wolfe (ISW) signature by cross-correlating the Fermi-LAT maps with the 7-year Wilkinson Microwave Anisotropy Probe (WMAP7) cosmic microwave background map. We find a cross-correlation consistent with zero, even though the expected signal is larger than that of the EGB auto-correlation. Finally, in an attempt to constrain the nature of the gamma-ray background, we cross-correlate the Fermi-LAT maps with the angular distributions of objects that may contribute to the EGB: quasi-stellar objects (QSOs) in the Sloan Digital Sky Survey Data Release 6 (SDSS-DR6) catalogue, NRAO VLA Sky Survey (NVSS) galaxies, Two Micron All Sky Survey (2MASS) galaxies and Luminous Red Galaxies (LRGs) in the SDSS catalogue. The cross-correlation is always consistent with zero, in agreement with theoretical expectations, but we find (with low statistical significance) some interesting features that may indicate that some specific classes of objects contribute to the EGB. A chi(2) analysis confirms that the correlation properties of the 21-month data do not provide strong constraints of the EGB origin. However, the results suggest that the situation will significantly improve with the 5- and 10-yr Fermi-LAT data. In future, the EGB analysis will then allow placing significant constraints on the nature of the EGB and might provide, in addition, a detection of the ISW signal.
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