8 research outputs found
Background model systematics for the Fermi GeV excess
The possible gamma-ray excess in the inner Galaxy and the Galactic center
(GC) suggested by Fermi-LAT observations has triggered a large number of
studies. It has been interpreted as a variety of different phenomena such as a
signal from WIMP dark matter annihilation, gamma-ray emission from a population
of millisecond pulsars, or emission from cosmic rays injected in a sequence of
burst-like events or continuously at the GC. We present the first comprehensive
study of model systematics coming from the Galactic diffuse emission in the
inner part of our Galaxy and their impact on the inferred properties of the
excess emission at Galactic latitudes and 300 MeV to 500
GeV. We study both theoretical and empirical model systematics, which we deduce
from a large range of Galactic diffuse emission models and a principal
component analysis of residuals in numerous test regions along the Galactic
plane. We show that the hypothesis of an extended spherical excess emission
with a uniform energy spectrum is compatible with the Fermi-LAT data in our
region of interest at CL. Assuming that this excess is the extended
counterpart of the one seen in the inner few degrees of the Galaxy, we derive a
lower limit of ( CL) on its extension away from the GC. We
show that, in light of the large correlated uncertainties that affect the
subtraction of the Galactic diffuse emission in the relevant regions, the
energy spectrum of the excess is equally compatible with both a simple broken
power-law of break energy GeV, and with spectra predicted by the
self-annihilation of dark matter, implying in the case of final
states a dark matter mass of GeV.Comment: 65 pages, 28 figures, 7 table
Nanomechanical torsional resonator torque magnetometry (invited)
Micromechanical resonators are very useful for detection of magnetic torque. We have developed nanoscale torsional resonators fabricated within silicon nitride membranes, as a platform for magnetometry of nanoscale magnetic elements. We describe the rotational magnetic hysteresis of a 10 nm thick film deposited on a resonator, and a study of magnetic hysteresis in a single, 1 m diameter permalloy disk. The torsional resonator is patterned using a dual beam scanning electron/focused ion system. For the 1 m diameter disk, it is found to be possible to tune the conditions such that an apparent magnetic supercooling of vortex nucleation is observed, as would be suggested by the modified Landau theory of the C- to vortex-state switch as a first-order phase transition. Complementary transmission electron and Lorentz microscopy of the same structures have also been performed. \ua9 2011 American Institute of Physics.Peer reviewed: YesNRC publication: Ye