230 research outputs found
Spectral and spatial variations of the diffuse gamma-ray background in the vicinity of the Galactic plane and possible nature of the feature at 130 GeV
We study the properties of the diffuse gamma-ray background around the
Galactic plane at energies 20 -- 200 GeV. We find that the spectrum of this
emission possesses significant spacial variations with respect to the average
smooth component. The positions and shapes of these spectral features change
with the direction on the sky. We therefore argue, that the spectral feature
around 130 GeV, found in several regions around the Galactic Center and in the
Galactic plane in [1203.1312, 1204.2797, 1205.1045, 1206.1616], can not be
interpreted with confidence as a gamma-ray line, but may be a component of the
diffuse background and can be of instrumental or astrophysical origin.
Therefore, the dark matter origin of this spectral feature becomes dubious.Comment: Extended analysis that further confirms the existence of several "hot
spots" around the Galactic plane and discussion of their possible origi
A comment on the emission from the Galactic Center as seen by the Fermi telescope
In the recent paper of Hooper & Goodenough (1010.2752) it was reported that
gamma-ray emission from the Galactic Center region contains an excess compared
to the contributions from the large-scale diffuse emission and known point
sources. This excess was argued to be consistent with a signal from
annihilation of Dark Matter with a power law density profile. We reanalyze the
Fermi data and find instead that it is consistent with the "standard model" of
diffuse emission and of known point sources. The main reason for the
discrepancy with the interpretation of 1010.2752 is different (as compared to
the previous works) spectrum of the point source at the Galactic Center assumed
in 1010.2752. We discuss possible reasons for such an interpretation
Constraining dark matter properties with SPI
Using the high-resolution spectrometer SPI on board the International Gamma-Ray Astrophysics Laboratory (INTEGRAL), we search for a spectral line produced by a dark matter (DM) particle with a mass in the range 40 keV < MDM < 14 MeV, decaying in the DM halo of the Milky Way. To distinguish the DM decay line from numerous instrumental lines found in the SPI background spectrum, we study the dependence of the intensity of the line signal on the offset of the SPI pointing from the direction toward the Galactic Centre. After a critical analysis of the uncertainties of the DM density profile in the inner Galaxy, we find that the intensity of the DM decay line should decrease by at least a factor of 3 when the offset from the Galactic Centre increases from 0° to 180°. We find that such a pronounced variation of the line flux across the sky is not observed for any line, detected with a significance higher than 3Ï in the SPI background spectrum. Possible DM decay origin is not ruled out only for the unidentified spectral lines, having low (âŒ3Ï) significance or coinciding in position with the instrumental ones. In the energy interval from 20 keV to 7 MeV, we derive restrictions on the DM decay line flux, implied by the (non-)detection of the DM decay line. For a particular DM candidate, the sterile neutrino of mass MDM, we derive a bound on the mixing angl
Technical comment on the paper of Dessert et al. "The dark matter interpretation of the 3.5 keV line is inconsistent with blank-sky observations"
An unidentified line at energy around 3.5 keV was detected in the spectra of
dark matter-dominated objects. Recent work of Dessert et al. [1812.06976] used
30 Msec of XMM-Newton blank-sky observations to constrain the admissible line
flux, challenging its dark matter decay origin. We demonstrate that these
bounds are overestimated by more than an order of magnitude due to improper
background modeling. Therefore the dark matter interpretation of the 3.5 keV
signal remains viable.Comment: Technical comment on the paper by Dessert et al.
10.1126/science.aaw377
Low secondary electron yield engineered surface for electron cloud mitigation
Secondary electron yield (SEY or Ύ) limits the performance of a number of devices. Particularly, in high-energy charged particle accelerators, the beam-induced electron multipacting is one of the main sources of electron cloud (e-cloud) build up on the beam path; in radio frequency wave guides, the electron multipacting limits their lifetime and causes power loss; and in detectors, the secondary electrons define the signal background and reduce the sensitivity. The best solution would be a material with a low SEY coating and for many applications Ύ < 1 would be sufficient. We report on an alternative surface preparation to the ones that are currently advocated. Three commonly used materials in accelerator vacuum chambers (stainless steel, copper, and aluminium) were laser processed to create a highly regular surface topography. It is shown that this treatment reduces the SEY of the copper, aluminium, and stainless steel from Ύmax of 1.90, 2.55, and 2.25 to 1.12, 1.45, and 1.12, respectively. The Ύmax further reduced to 0.76-0.78 for all three treated metals after bombardment with 500 eV electrons to a dose between 3.5 à 10-3 and 2.0 à 10-2 C·mm-2
A Facility For Magnetic Field Penetration Measurements on Multilayer S-I-S Structures
Superconducting RF cavities made of bulk Nb has reached a breakdown field of about 200 mT which is close to the superheating field for Nb. As it was theoretically shown a multilayer coating can be used to enhance the breakdown field of SRF cavities. The simple example is a superconductor-insulator-superconductor (S-I-S), for example bulk niobium (S) coated with a thin film of insulator (I) followed by a thin layer of a superconductor (S) which could be a dirty niobium. To verify such an enhancement in a presence of a DC magnetic field at 4.2 K a simple experimental facility was designed, built and tested in ASTeC. The details of experimental setup and results of the measurements will be shown at the conference
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