Bulletin of the American Physical Society
APS April Meeting 2016
Volume 61, Number 6
Saturday–Tuesday, April 16–19, 2016; Salt Lake City, Utah
Session E13: Dark Matter, Indirect, Gamma-rays |
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Chair: Miquel Sanchez-Conde, Stockholm University Room: 250F |
Saturday, April 16, 2016 3:30PM - 3:42PM |
E13.00001: Looking for the Northern Fermi Bubble with HAWC Hugo Ayala, Hao Zhou, Petra Huentemeyer The Fermi Bubbles were discovered in the GeV gamma-ray data from the Fermi Telescope in 2010. They extend up to 55$^o$ above and below the Galactic Center forming two large and homogeneous regions of spectrally hard gamma-ray emission. Understanding the mechanisms which produce the observed hard spectrum will help understand the origin of the Fermi Bubbles. Both hadronic and leptonic models can describe the spectrum of the bubbles, though the leptonic model can explain similar structures observed in microwave data from the WMAP and Planck satellites. Recent publications show that the spectrum of the Fermi Bubbles is well described by a power law with an exponential cutoff between 100MeV to 500GeV. Observing the Fermi Bubbles at higher gamma-ray energies will help constrain their spectrum. A steeper cutoff will favor a leptonic model. The High Altitude Water Cherenkov (HAWC) Observatory, located 4100m above sea level in Mexico, is designed to measure high-energy gamma rays between 100GeV to 100TeV. With a large field of view and good sensitivity to spatially extended sources, HAWC is the ground-based observatory best suited to detect extended regions like the Fermi Bubbles. We present a search for emission from the Fermi Bubble visible to HAWC. [Preview Abstract] |
Saturday, April 16, 2016 3:42PM - 3:54PM |
E13.00002: ABSTRACT WITHDRAWN |
Saturday, April 16, 2016 3:54PM - 4:06PM |
E13.00003: Gamma-ray Signal from Dark Matter Annihilation Mediated by Mixing Slepton Fei Teng In order to reconcile the tension between the collider SUSY particle search and the dark matter relic density constraint, we free ourselves from the simplest CMSSM model and find a large parameter space in which a sub-TeV bino dark matter may comply with all the current experimental constraints. In this so-called incredible bulk region, dark matter mainly annihilates through the $t$ channel exchange of a mixing slepton into a leptonic final state. We have explored this proposal and studied the resultant spectrum feature. We are going to show that the line signal produced by the $\gamma\gamma$ and $\gamma Z$ final state will give some indications to the mixing angle and CP-violation phase of the slepton sector. On the other hand, internal bremsstrahlung (IB) feature will be easier to get observed by future experiments, with sensitivity around $10^{-29}\text{cm}^{3}/\text{s}$. Unlike some other models, our IB signal is dominated by the collinear limit of the final state radiation amplitude and shows a bump-like feature. [Preview Abstract] |
Saturday, April 16, 2016 4:06PM - 4:18PM |
E13.00004: Gamma-ray signals from weak scale SUSY dark matter Takahiro Yamamoto, Pearl Sandick, Fei Teng, Jason Kumar It is widely thought that recent results for supersymmetry and dark matter searches favor TeV-scale SUSY Standard Model. In this talk, however, I will argue that there still exists a wide range of viable parameter space of weak scale MSSM. This model predicts new bulk region in which relatively light sleptons with the large chiral mixing and $CP$-violating phase enhance the dark matter annihilation into lepton pair, and is severely tested by the precise measurements of magnetic and electric dipole moment of leptons. I will conclude my talk by presenting the possible signatures from such dark matter particles at the present epoch and exploring the detectability of the signals using the currently operating and next generation satellite gamma-ray telescopes. [Preview Abstract] |
Saturday, April 16, 2016 4:18PM - 4:30PM |
E13.00005: The High Altitude Water Cherenkov Observatory Miguel Mostafa The High Altitude Water Cherenkov (HAWC) Observatory is a continuously operated, wide field of view experiment comprised of an array of 300 water Cherenkov detectors (WCDs) to study transient and steady emission of TeV gamma and cosmic rays. Each 200000~l WCD is instrumented with 4 PMTs providing charge and timing information. The array covers $\sim$22000~m$^2$ at an altitude of 4100~m a.s.l.\ inside the Pico de Orizaba national park in Mexico. The high altitude, large active area, and optical isolation of the PMTs allows us to reliably estimate the energy and determine the arrival direction of gamma and cosmic rays with significant sensitivity over energies from several hundred GeV to a hundred TeV. Continuously observing $2/3$ of the sky every 24~h, HAWC plays a significant role as a survey instrument for multi-wavelength studies. The performance of HAWC makes possible the detection of both transient and steady emissions, the study of diffuse emission and the measurement of the spectra of gamma-ray sources at TeV energies. HAWC is also sensitive to the emission from GRBs above 100~GeV. I will highlight the results from the first year of operation of the full HAWC array, and describe the ongoing site work to expand the array by a factor of 4 to explore the high energy range. [Preview Abstract] |
Saturday, April 16, 2016 4:30PM - 4:42PM |
E13.00006: The HAWC Sensitivity to Dark Matter Annihilation and Decay Tolga Yapici The High Altitude Water Cherenkov (HAWC) Observatory is an extensive air shower array in the state of Puebla, Mexico at an altitude of 4100m. The HAWC observatory will perform an indirect search for dark matter via GeV-TeV photons resulting from dark matter annihilation and decay, including annihilation from extended dark matter sources. We consider the HAWC sensitivity to a subset of the sources, including the M31 galaxy, the Virgo cluster, and the Galactic center. We simulate the HAWC response to gamma rays from the sources in well-motivated dark matter annihilation channels. We show the limits HAWC can place on the dark matter cross-section or lifetime from these sources if gamma-ray excess is not observed. In particular, for dark matter annihilating into gauge bosons, HAWC will be able to measure a narrow range of dark matter masses to cross-sections below that expected for a thermal relic. HAWC should also be sensitive to cross-sections higher than thermal for masses up to nearly 1000 TeV. HAWC will be sensitive to decaying dark matter for these masses as well. HAWC can explore higher dark matter masses than are currently constrained. [Preview Abstract] |
Saturday, April 16, 2016 4:42PM - 4:54PM |
E13.00007: The search for dark matter in dwarf galaxies with HAWC Patrick Harding The High Altitude Water Cherenkov (HAWC) gamma-ray observatory is a wide field-of-view observatory sensitive to 100 GeV – 100 TeV gamma-rays and cosmic-rays. Among the signals that HAWC should be sensitive to are possible gamma-ray emissions from dark matter annihilation and decay. With its high energy reach and large field-of-view, HAWC is able to search many objects for signals of gamma-rays from high-mass dark matter, with masses up to 1000 TeV. One promising class of objects in which to search for such indirect detection of dark matter are dwarf spheroidal galaxies, which are expected to have few astrophysical gamma-ray sources but large dark matter content. Here we present early HAWC limits on the dark matter annihilation cross-section and decay lifetime from 14 dwarf spheroidal galaxies within the HAWC field-of-view, including a combined limit using all 14 galaxies. HAWC is able to limit higher dark matter masses than have been previously studied. [Preview Abstract] |
Saturday, April 16, 2016 4:54PM - 5:06PM |
E13.00008: Implications of the Observed Scaling Relations between the Dark Matter Halo Parameters and Half-Light Radii of Milky Way Dwarf Spheroidals. Zechariah Miller, Hunter Somers, Ben Woodall, Casey Watson We compare observed scaling relationships between the half-light radii and best-fit, Burkert dark matter halo parameters of 13 Milky Way dwarf spheroidal galaxies (dSphs) to similar relationships found for dwarf spiral galaxies. We also consider the theoretical underpinnings of these relationships and discuss their implications for galaxy formation and evolution. [Preview Abstract] |
Saturday, April 16, 2016 5:06PM - 5:18PM |
E13.00009: Diffuse gamma-ray emission modeling near the Galactic Center and the 3 GeV excess Andrea Albert, Dmitry Maleshev, Anna Franckowiak, Luigi Tibaldo Several groups have reported excess emission in gamma rays peaking around 3 GeV relative to expectations from conventional models for the interstellar emission in the Galactic Center (GC). We study the uncertainty of the excess emission in Pass 8 Fermi-LAT data due to modeling of the various emission components in that direction. In particular, we quantify the uncertainties on the excess by refitting with several GALPROP models of Galactic diffuse emission, an alternative distribution of gas along the line of sight based on starlight extinction data, a model of the Fermi bubbles at low latitudes, and including templates for additional sources of cosmic-ray electrons near the GC. In all models that we have tested the excess emission remains significant. The origin of the excess is currently uncertain. To test the robustness of a dark-matter interpretation, we perform fits in controls regions along the Galactic Plane. The uncertainties from our fits in control regions have a similar relative size as the excess in the GC. Therefore a non-dark-matter explanation cannot be ruled out and we consequently set limits on the dark matter annihilation cross section. [Preview Abstract] |
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