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Register a new userMAGIC search for VHE $gamma$-ray emission from AE Aquarii in a multiwavelength context
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Added by
Rub\\'en L\\'opez-Coto
Publication date
2014
fields
Physics
and research's language is
English
Authors
J. Aleksic
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It has been claimed that the nova-like cataclysmic variable (CV) AE Aquarii (AE Aqr) is a very-high-energy (VHE, $E>$100 GeV) source both on observational and theoretical grounds. We aim to search for VHE gamma-ray emission from AE Aqr during different states of the source at several wavelengths to confirm or rule out previous claims of detection of gamma-ray emission from this object. We report on observations of AE Aqr performed by MAGIC. The source was observed during 12 hours as part of a multiwavelength campaign carried out between May and June 2012 covering the optical, X-ray, and gamma-ray ranges. Besides MAGIC, the other facilities involved were the KVA, Skinakas, and Vidojevica telescopes in the optical and Swift in X-rays. We calculated integral upper limits coincident with different states of the source in the optical. We computed upper limits to the pulsed emission limiting the signal region to 30% of the phaseogram and we also searched for pulsed emission at different frequencies applying the Rayleigh test. AE Aqr was not detected at VHE energies during the multiwavelength campaign. We establish integral upper limits at the 95% confidence level for the steady emission assuming the differential flux proportional to a power-law function dphi/dE propto E^{-Gamma}, with a Crab-like photon spectral index of Gamma=2.6. The upper limit above 200 GeV is 6.4times10^{-12} cm^{-2}s^{-1} and above 1 TeV is 7.4times10^{-13} cm^{-2}s^{-1}. We obtained an upper limit for the pulsed emission of 2.6times10^{-12} cm^{-2}s^{-1} for energies above 200 GeV. Applying the Rayleigh test for pulsed emission at different frequencies we did not find any significant signal. Our results indicate that AE Aqr is not a VHE gamma-ray emitter at the level of emission previously claimed. We have established the most constraining upper limits for the VHE gamma-ray emission of AE Aqr.
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Indirect dark matter searches with ground-based gamma-ray observatories provide an alternative for identifying the particle nature of dark matter that is complementary to that of direct search or accelerator production experiments. We present the results of observations of the dwarf spheroidal galaxies Draco, Ursa Minor, Bootes 1, and Willman 1 conducted by VERITAS. These galaxies are nearby dark matter dominated objects located at a typical distance of several tens of kiloparsecs for which there are good measurements of the dark matter density profile from stellar velocity measurements. Since the conventional astrophysical background of very high energy gamma rays from these objects appears to be negligible, they are good targets to search for the secondary gamma-ray photons produced by interacting or decaying dark matter particles. No significant gamma-ray flux above 200 GeV was detected from these four dwarf galaxies for a typical exposure of ~20 hours. The 95% confidence upper limits on the integral gamma-ray flux are in the range 0.4-2.2x10^-12 photons cm^-2s^-1. We interpret this limiting flux in the context of pair annihilation of weakly interacting massive particles and derive constraints on the thermally averaged product of the total self-annihilation cross section and the relative velocity of the WIMPs. The limits are obtained under conservative assumptions regarding the dark matter distribution in dwarf galaxies and are approximately three orders of magnitude above the generic theoretical prediction for WIMPs in the minimal supersymmetric standard model framework. However significant uncertainty exists in the dark matter distribution as well as the neutralino cross sections which under favorable assumptions could further lower the limits.
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