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Nicolas Canac --- Astrophysical and Dark Matter Interpretations of Extended Gamma Ray Emission from the Galactic Center. Abstract
Toggle Cloak Cloak We construct empirical models of the diffuse gamma-ray background toward the Galactic Center. Including all known point sources and a template of emission associated with interactions of cosmic rays with molecular gas, we show that the extended emission observed previously in the Fermi Large Area Telescope data toward the Galactic Center is detected at high significance for all permutations of the diffuse model components. However, we find that the fluxes and spectra of the sources in our model change significantly depending on the background model. In particular, the spectrum of the central Sgr A_ source is less steep than in previous works and the recovered spectrum of the extended emission has large systematic uncertainties, especially at lower energies. If the extended emission is interpreted to be due to dark matter annihilation, we find annihilation into pure b-quark and _-lepton channels to be statistically equivalent goodness-of-fits. In the case of the pure b-quark channel, we find a dark matter mass of 39.4(+3.7_2.9 stat.)(±7.9 sys.) GeV, while a pure _+__ channel case has an estimated dark matter mass of 9.43(+0.63_0.52 stat.)(±1.2 sys.) GeV. Alternatively, if the extended emission is interpreted to be astrophysical in origin such as due to unresolved millisecond pulsars, we obtain strong bounds on dark matter annihilation, although systematic uncertainties due to the dependence on the background models are significant. Tansu Daylan --- The Characterization of the Gamma-Ray Signal from the Central Milky Way: A Compelling Case for Annihilating Dark Matter. Abstract
SlidesToggle Cloak Cloak Past studies have identified a spatially extended excess of ~1-3 GeV gamma rays from the region surrounding the Galactic Center, consistent with the emission expected from annihilating dark matter. We revisit and scrutinize this signal with the intention of further constraining its characteristics and origin. By applying cuts to the Fermi event parameter CTBCORE, we suppress the tails of the point spread function and generate high resolution gamma-ray maps, enabling us to more easily separate the various gamma-ray components. Within these maps, we find the GeV excess to be robust and highly statistically significant, with a spectrum, angular distribution, and overall normalization that is in good agreement with that predicted by simple annihilating dark matter models. For example, the signal is very well fit by a 31-40 GeV dark matter particle annihilating to b quarks with an annihilation cross section of sigma v = (1.4-2.0) x 10^-26 cm^3/s (normalized to a local dark matter density of 0.3 GeV/cm^3). Furthermore, we confirm that the angular distribution of the excess is approximately spherically symmetric and centered around the dynamical center of the Milky Way (within ~0.05 degrees of Sgr A*), showing no sign of elongation along or perpendicular to the Galactic Plane. The signal is observed to extend to at least 10 degrees from the Galactic Center, disfavoring the possibility that this emission originates from millisecond pulsars. Lelah Sadeghian --- Dark matter distributions around massive black holes: A fully general relativistic approach. Abstract
SlidesToggle Cloak Cloak The cold dark matter at the center of a galaxy will be redistributed by the presence of a massive black hole. The redistribution may be determined by beginning with a model distribution function for the dark matter, and “growing” the black hole adiabatically, holding the adiabatic invariants of the motion constant. Unlike previous approaches, which adopted Newtonian theory together with ad hoc correction factors to mimic general relativistic effects, we carry out the calculation fully relativistically, using the exact Schwarzschild geometry of the black hole. We consider a range of initial distribution functions, including “cuspy” profiles, and find that the density spike very close to the black hole is significantly higher than that found previously by Newtonian analyses. The potential implications for detection of signals from galactic center dark matter will be discussed. - 1 Slide:
Mon. June 2
Siraprapa Sanpa-arsa --- Green Bank Telescope (GBT) Radio Millisecond Pulsars Searches in Fermi unassociated LAT sources. Abstract
SlidesToggle Cloak Cloak After Fermi launched in 2008, it has revolutionized gamma-ray pulsar astronomy, by enabling the discovery of many new millisecond pulsars (MSPs). The Fermi Pulsar Search Consortium (PSC) has organized hundreds of radio observations of pulsar-like Large Area Telescope (LAT) unassociated gamma-ray sources. In about 4 years, the PSC has discovered 64 new MSPs. These new discoveries number more than all MSPs in the first 20 years (from 1982 to 2002) of MSP searching combined. Notably, among the 64 new MSPs, there are at least 13 “black widows” and 4 “redbacks” (the rare populations of eclipsing pulsar binaries). As one of the PSC radio telescopes, the Green Bank Telescope (GBT) has, outstandingly, helped uncover 35 new MSPs. By searching more Fermi unassociated sources from the LAT 1-year, 2-year and soon 3-year Point Source Catalog, the GBT will almost certainly discover additional MSPs. The newly discovered MSPs will provide more potential additions to the pulsar timing arrays (like NANOGrav) as well as improve the understanding of MSP formation and evolution. Andrew McCann --- VHE Emission from Gamma-ray pulsars. Abstract
SlidesToggle Cloak Cloak NASA's Fermi space telescope has provided us with a bountiful new population of gamma-ray sources following its discovery of 140 new gamma-ray pulsars. One common feature exhibited by all of these pulsars is the form of their spectral energy distribution, which can
be described by a power law followed by a spectral break occurring between ~1 and ~8 GeV. The unanimity of the break energy across the entire Fermi pulsar sample suggests that the sites of acceleration and processes of gamma-ray emission are common across the different pulsar types. The common wisdom is that the break is followed by an exponential cut-off driven by radiation/reaction-limited curvature emission. The discovery of pulsed gamma rays from the Crab pulsar, the only pulsar so far detected at very high energies (E>100GeV), contradicts this "cut-off" picture. In this talk I will review, from
an observational stand point, what we know about the emission of pulsars at VHE energies.- 1 Slide:
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