Veritas Search for Vhe Gamma-Ray Emission From Dwarf Spheroidal Galaxies

Abstract

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, Boötes 1, and Willman 1 conducted by the Very Energetic Radiation Imaging Telescope Array System (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 hr. The 95% confidence upper limits on the integral gamma-ray flux are in the range (0.4-2.2) × 10 −12 photons cm −2 s −1 . We interpret this limiting flux in the context of pair annihilation of weakly interacting massive particles (WIMPs) and derive constraints on the thermally averaged product of the total self-annihilation cross section and the relative velocity of the WIMPs ( σ v 10 −23 cm 3 s −1 for m χ 300 GeV c −2 ). This limit is obtained under conservative assumptions regarding the dark matter distribution in dwarf galaxies and is approximately 3 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 this limit.

H.E.S.S. constraints on dark matter annihilations towards the sculptor and carina dwarf galaxies

“…H.E.S.S. limits are comparable to the limits reported by MAGIC [49] and VERITAS [50], but weaker than those obtained by Fermi-LAT [11] in the GeV mass range. Nevertheless, they are complementary to the Fermi-LAT limits in the TeV range.…”

Search for dark matter from the Galactic halo with the IceCube Neutrino Telescope

“…VERITAS observed no significant gamma-ray excess from four dwarf spheroidals and derived an upper limit on the gamma-ray flux to constrain the self-annihilation cross section as a function of WIMP mass. The limit reduces to 10 −22 cm 3 s −1 for a WIMP mass of 300 GeV [60]. H.E.S.S.…”

Optimized Dark Matter Searches in Deep Observations of Segue 1 with MAGIC

“…Over the last decade, a number of dSphs have been observed by the present generation of IACTs: MAGIC [17][18][19], H.E.S.S. [20][21][22] and VERITAS [23,24], as well as by the Large Area Telescope (LAT) on board the Fermi satellite [25].…”