Fermi LAT Search for Photon Lines from 30 to 200 GeV and Dark Matter Implications

Dark matter (DM) particle annihilation or decay can produce monochromatic $\gamma$-rays readily distinguishable from astrophysical sources. $\gamma$-ray line limits from 30 GeV to 200 GeV obtained from 11 months of Fermi Large Area Space Telescope data from 20-300 GeV are presented using a selection based on requirements for a $\gamma$-ray line analysis, and integrated over most of the sky. We obtain $\gamma$-ray line flux upper limits in the range $0.6-4.5\times 10^{-9}\mathrm{cm}^{-2}\mathrm{s}^{-1}$, and give corresponding DM annihilation cross-section and decay lifetime limits. Theoretical implications are briefly discussed.Comment: 6 pages, 1 figure. Accepted for publication by The Physical Review Letter

Associating long-term γ-ray variability with the superorbital period of LS I + 61◦ 303

Gamma-ray binaries are stellar systems for which the spectral ene rgy distribu- tion (discounting the thermal stellar emission) peaks at high energie s. Detected from radio to TeV gamma rays, the γ -ray binary LS I +61 ◦ 303 is highly variable across all frequencies. One aspect of this system's variability is the modula- tion of its emission with the timescale set by the ∼ 26 . 4960-day orbital period. Here we show that, during the time of our observations, the γ -ray emission of LS I +61 ◦ 303 also presents a sinusoidal variability consistent with the previou sly- known superorbital period of 1667 days. This modulation is more pro minently seen at orbital phases around apastron, whereas it does not intr oduce a visible change close to periastron. It is also found in the appearance and d isappearance of variability at the orbital period in the power spectrum of the data . This be- havior could be explained by a quasi-cyclical evolution of the equator ial outflow of the Be companion star, whose features influence the conditions for generating gamma rays. These findings open the possibility to use γ -ray observations to study the outflows of massive stars in eccentric binary systems

Measurement of the Cosmic Ray e(+)+e(-) Spectrum from 20 GeV to 1 TeV with the Fermi Large Area Telescope

Designed as a high-sensitivity gamma-ray observatory, the Fermi Large Area Telescope is also an electron detector with a large acceptance exceeding 2 m2 sr at 300 GeV. Building on the gamma-ray analysis, we have developed an efficient electron detection strategy which provides sufficient background rejection for measurement of the steeply falling electron spectrum up to 1 TeV. Our high precision data show that the electron spectrum falls with energy as E-3.0 and does not exhibit prominent spectral features. Interpretations in terms of a conventional diffusive model as well as a potential local extra component are briefly discussed