E. Bonamente

Dark Matter Constraints from Observations of 25 Milky Way Satellite Galaxies with the Fermi Large Area Telescope

The dwarf spheroidal satellite galaxies of the Milky Way are some of the most dark-matter-dominated objects known. Due to their proximity, high dark matter content, and lack of astrophysical backgrounds, dwarf spheroidal galaxies are widely considered to be among the most promising targets for the indirect detection of dark matter via γ rays. Here we report on γ-ray observations of 25 Milky Way dwarf spheroidal satellite galaxies based on 4 years of Fermi Large Area Telescope (LAT) data. None of the dwarf galaxies are significantly detected in γ rays, and we present γ-ray flux upper limits between 500 MeV and 500 GeV. We determine the dark matter content of 18 dwarf spheroidal galaxies from stellar kinematic data and combine LAT observations of 15 dwarf galaxies to constrain the dark matter annihilation cross section. We set some of the tightest constraints to date on the annihilation of dark matter particles with masses between 2 GeV and 10 TeV into prototypical standard model channels. We find these results to be robust against systematic uncertainties in the LAT instrument performance, diffuse γ-ray background modeling, and assumed dark matter density profile.

Observations of MilkyWay Dwarf Spheroidal galaxies with the Fermi-LAT detector and

We report on the observations of 14 dwarf spheroidal galaxies with the Fermi Gamma-Ray Space Telescope taken during the first 11 months of survey mode operations. The Fermi telescope provides a new opportunity to test particle dark matter models through the expected gamma-ray emission produced by pair annihilation of weakly interacting massive particles (WIMPs). Local Group dwarf spheroidal galaxies, the largest galactic substructures predicted by the cold dark matter scenario, are attractive targets for such indirect searches for dark matter because they are nearby and among the most extreme dark matter dominated environments. No significant gamma-ray emission was detected above 100 MeV from the candidate dwarf galaxies. We determine upper limits to the gamma-ray flux assuming both power-law spectra and representative spectra from WIMP annihilation. The resulting integral flux above 100 MeV is constrained to be at a level below around 10^-9 photons cm^-2 s^-1. Using recent stellar kinematic data, the gamma-ray flux limits are combined with improved determinations of the dark matter density profile in 8 of the 14 candidate dwarfs to place limits on the pair annihilation cross-section of WIMPs in several widely studied extensions of the standard model. With the present data, we are able to rule out large parts of the parameter space where the thermal relic density is below the observed cosmological dark matter density and WIMPs (neutralinos here) are dominantly produced non-thermally, e.g. in models where supersymmetry breaking occurs via anomaly mediation. The gamma-ray limits presented here also constrain some WIMP models proposed to explain the Fermi and PAMELA e^+e^- data, including low-mass wino-like neutralinos and models with TeV masses pair-annihilating into muon-antimuon pairs. (Abridged)

Fermi LAT Search for Photon Lines from 30 to 200 GeV

Dark matter (DM) particle annihilation or decay can produce monochromatic gamma rays readily distinguishable from astrophysical sources. gamma-ray line limits from 30 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 0.6-4.5x10{-9} cm{-2} s{-1}, and give corresponding DM annihilation cross-section and decay lifetime limits. Theoretical implications are briefly discussed.

FERMI LARGE AREA TELESCOPE STUDY OF COSMIC RAYS AND THE INTERSTELLAR MEDIUM IN NEARBY MOLECULAR CLOUDS

We report an analysis of the interstellar γ -ray emission from the Chamaeleon, R Coronae Australis (R CrA), and Cepheus and Polaris flare regions with the Fermi Large Area Telescope. They are among the nearest molecular cloud complexes, within ∼300 pc from the solar system. The γ -ray emission produced by interactions of cosmic rays (CRs) and interstellar gas in those molecular clouds is useful to study the CR densities and distributions of molecular gas close to the solar system. The obtained γ -ray emissivities above 250 MeV are (5.9 ± 0.1stat +0.9 −1.0sys) × 10−27 photons s−1 sr−1 H-atom−1, (10.2 ± 0.4stat +1.2 −1.7sys) × 10−27 photons s−1 sr−1 H-atom−1, and (9.1 ± 0.3stat +1.5 −0.6sys) × 10−27 photons s−1 sr−1 H-atom−1 for the Chamaeleon, R CrA, and Cepheus and Polaris flare regions, respectively. Whereas the energy dependences of the emissivities agree well with that predicted from direct CR observations at the Earth, the measured emissivities from 250 MeV to 10 GeV indicate a variation of the CR density by ∼20% in the neighborhood of the solar system, even if we consider systematic uncertainties. The molecular mass calibrating ratio, XCO = N(H2)/WCO, is found to be (0.96 ± 0.06stat +0.15 −0.12sys) × 1020 H2-molecule cm−2 (K km s−1)−1, (0.99 ± 0.08stat +0.18 −0.10sys) × 1020 H2-molecule cm−2 (K km s−1)−1, and (0.63 ± 0.02stat +0.09 −0.07sys) × 1020 H2-molecule cm−2 (K km s−1)−1 for the Chamaeleon, R CrA, and Cepheus and Polaris flare regions, respectively, suggesting a variation of XCO in the vicinity of the solar system. From the obtained values of XCO, the masses of molecular gas traced by WCO in the Chamaeleon, R CrA, and Cepheus and Polaris flare regions are estimated to be ∼5 × 103M , ∼103M , and ∼3.3 × 104M , respectively. A comparable amount of gas not traced well by standard Hi and CO surveys is found in the regions investigated.We report an analysis of the interstellar γ-ray emission from the Chamaeleon, R Coronae Australis (R CrA), and Cepheus and Polaris flare regions with the Fermi Large Area Telescope. They are among the nearest molecular cloud complexes, within ∼ 300 pc from the solar system. The γ-ray emission produced by interactions of cosmicrays (CRs) and interstellar gas in those molecular clouds is useful to study the CR densities and distributions of molecular gas close to the solar system. The obtained γ-ray emissivities above 250 MeV are (5.9 ± 0.1stat +0.9 −1.0sys) × 10 −27 photons s−1 sr−1 H-atom−1, (10.2 ± 0.4stat +1.2 −1.7sys) × 10 −27 photons s−1 sr−1 H-atom−1, and (9.1 ± 0.3stat +1.5 −0.6sys) × 10 −27 photons s−1 sr−1 H-atom−1 for the Chamaeleon, R CrA, and Cepheus and Polaris flare regions, respectively. Whereas the energy dependences of the emissivities agree well with that predicted from direct CR observations at the Earth, the measured emissivities from 250 MeV to 10 GeV indicate a variation of the CR density by ∼ 20 % in the neighborhood of the solar system, even if we consider systematic uncertainties. The molecular mass calibrating ratio, XCO = N(H2)/WCO, is found to be (0.96 ± 0.06stat +0.15 −0.12sys) ×10 20 H2-molecule cm −2 (K km s−1)−1, (0.99 ± 0.08stat +0.18 −0.10sys) ×10 20 H2-molecule cm −2 (K km s−1)−1, and (0.63 ± 0.02stat +0.09 −0.07sys) ×10 20 H2-molecule cm −2 (K km s−1)−1 for the Chamaeleon, R CrA, and Cepheus and Polaris flare regions, respectively, suggesting a variation of XCO in the vicinity of the solar system. From the obtained values of XCO, the masses of molecular gas traced by WCO in the Chamaeleon, R CrA, and Cepheus and Polaris flare regions are estimated to be ∼ 5×103 M⊙, ∼ 10 3 M⊙, and ∼ 3.3×10 4 M⊙, respectively. A comparable amount of gas not traced well by standard H I and CO surveys is found in the regions investigated. University of California at Santa Cruz, Santa Cruz, CA 95064, USA Institut für Astround Teilchenphysik and Institut für Theoretische Physik, Leopold-Franzens-Universität Innsbruck, A-6020 Innsbruck, Austria Department of Physics, University of Washington, Seattle, WA 98195-1560, USA NYCB Real-Time Computing Inc., Lattingtown, NY 11560-1025, USA Department of Chemistry and Physics, Purdue University Calumet, Hammond, IN 46323-2094, USA Institut für Theoretische Physik and Astrophysik, Universität Würzburg, D-97074 Würzburg, Germany Institució Catalana de Recerca i Estudis Avançats (ICREA), Barcelona, Spain Consorzio Interuniversitario per la Fisica Spaziale (CIFS), I-10133 Torino, Italy INTEGRAL Science Data Centre, CH-1290 Versoix, Switzerland NASA Postdoctoral Program Fellow, USA Dipartimento di Fisica, Università di Roma “Tor Vergata”, I-00133 Roma, Italy Institut Universitaire de France, France

Preliminary results of the LAT Calibration Unit beam tests

The calibration strategy of the GLAST Large Area Telescope (LAT) combines analysis of cosmic ray data with accelerator particle beams measurements. An advanced Monte Carlo simulation of the LAT, based on the Geant4 package, was set up to reproduce the LAT response to such radiation and to benchmark the event reconstruction and the background rejection strategy before launch and during operation. To validate the LAT simulation, a massive campaign of beam tests was performed between July and November 2006, in parallel with the LAT integration and test, on the LAT Calibration Unit. This is a detector built with spare flight modules and flight‐like readout electronics, which was exposed to a large variety of beams, representing the whole spectrum of the signal that will be detected by the LAT, using the CERN and the GSI accelerator facilities. Beams of photons (0 – 2.5 GeV), electrons (1 – 300 GeV), hadrons (π and p, a few GeV – 100 GeV) and ions (C; Xe, 1.5 GeV/n) were shot through the CU to measure the phys...

Fermi Large Area Telescope Observations of Markarian 421

We report on the gamma-ray activity of the high-synchrotron-peaked BL Lacertae object Markarian 421 (Mrk 421) during the first 1.5 years of Fermi operation, from 2008 August 5 to 2010 March 12. We find that the Large Area Telescope (LAT) gamma-ray spectrum above 0.3 GeV can be well described by a power-law function with photon index Gamma = 1.78 +/- 0.02 and average photon flux F(>0.3 GeV) = (7.23 +/- 0.16) x 10(-8) ph cm(-2) s(-1). Over this time period, the Fermi-LAT spectrum above 0.3 GeV was evaluated on seven-day-long time intervals, showing significant variations in the photon flux (up to a factor similar to 3 from the minimum to the maximum flux) but mild spectral variations. The variability amplitude at X-ray frequencies measured by RXTE/ASM and Swift/BAT is substantially larger than that in gamma-rays measured by Fermi-LAT, and these two energy ranges are not significantly correlated. We also present the first results from the 4.5 month long multifrequency campaign on Mrk 421, which included the VLBA, Swift, RXTE, MAGIC, the F-GAMMA, GASP-WEBT, and other collaborations and instruments that provided excellent temporal and energy coverage of the source throughout the entire campaign (2009 January 19 to 2009 June 1). During this campaign, Mrk 421 showed a low activity at all wavebands. The extensive multi-instrument (radio to TeV) data set provides an unprecedented, complete look at the quiescent spectral energy distribution (SED) for this source. The broadband SED was reproduced with a leptonic (one-zone synchrotron self-Compton) and a hadronic model (synchrotron proton blazar). Both frameworks are able to describe the average SED reasonably well, implying comparable jet powers but very different characteristics for the blazar emission site.We report on the γ -ray activity of the high-synchrotron-peaked BL Lacertae object Markarian 421 (Mrk 421) during the first 1.5 years of Fermi operation, from 2008 August 5 to 2010 March 12. We find that the Large Area Telescope (LAT) γ -ray spectrum above 0.3 GeV can be well described by a power-law function with photon index Γ = 1.78± 0.02 and average photon flux F (>0.3 GeV) = (7.23 ± 0.16) × 10−8 ph cm−2 s−1. Over this time period, the FermiLAT spectrum above 0.3 GeV was evaluated on seven-day-long time intervals, showing significant variations in the photon flux (up to a factor ∼3 from the minimum to the maximum flux) but mild spectral variations. The variability amplitude at X-ray frequencies measured by RXTE/ASM and Swift/BAT is substantially larger than that in γ -rays measured by Fermi-LAT, and these two energy ranges are not significantly correlated. We also present the first results from the 4.5 month long multifrequency campaign on Mrk 421, which included the VLBA, Swift, RXTE, MAGIC, the F-GAMMA, GASP-WEBT, and other collaborations and instruments that provided excellent temporal and energy coverage of the source throughout the entire campaign (2009 January 19 to 2009 June 1). During this campaign, Mrk 421 showed a low activity at all wavebands. The extensive multi-instrument (radio to TeV) data set provides an unprecedented, complete look at the quiescent spectral energy distribution (SED) for this source. The broadband SED was reproduced with a leptonic (one-zone synchrotron self-Compton) and a hadronic model (synchrotron proton blazar). Both frameworks are able to describe the average SED reasonably well, implying comparable jet powers but very different characteristics for the blazar emission site.

Calibration of the HAWC observatory

The HAWC (High Altitude Water Cherenkov) observatory is a 2 generation, high-sensitivity gamma ray observatory building on experience from its predecessor, the Milagro observatory. In both observatories, water-cherenkov photons produced by air shower particles are detected and their arrival times at the photo multipliers are used to reconstruct the shower plane and direction. In HAWC, 300 7.3 meter diameter × 4.5 meter deep water tanks are each filled with water and placed in close proximity (∼1 m separation). Each tank has 3 upward-looking, 8”-diameter PMTs positioned ∼0.5 meters from the bottom of the tank. The reconstruction of the initial gamma ray direction is highly dependent on the relative time differences between different tanks and PMT channels. In this paper, a calibration system is presented, modeled on the Milagro calibration system, using a pulsing laser with 300 ps long pulses. Pulses are directed into fiber optic cables, which are split and directed to 1/15 of the tanks in the array at a time. For measuring PMT slewing times, neutral density filters will provide a range of laser intensities across 6 orders of magnitude. This system is planned to run autonomously in two different modes, for slow(∼5 Hz) laser pulsing at one light intensity, and for fast (∼200 Hz) laser pulsing across several different intensities. We will report on recent studies made in Spring 2011 using the HAWC prototype water Cherenkov detector at Colorado State University to evaluate the performance of the calibration system.