New H.E.S.S. diffuse emission from the Galactic center

Lacroix et al. (2016) show that the newly detected H.E.S.S. (High Energy Stereoscopic System) gamma-ray diffuse emission from the Galactic center below 0.45 deg can be accounted for by inverse Compton emission from millisecond pulsars and heavy (~ 100 TeV) dark matter annihilating to electrons or muons with a thermal or sub-thermal cross-section, provided that the dark matter density profile features a supermassive black hole-induced spike on sub-pc scales.

Image: Center of our Galaxy. Credit: NASA, ESA, SSC, CXC, and STScI

They discuss the impact of the interstellar radiation field, magnetic field and diffusion set-up on the spectral and spatial morphology of the resulting emission. For well-motivated parameters, they show that the DM-induced emission reproduces the spatial morphology of the H.E.S.S. signal above ~ 10 TeV, while they obtain a more extended component from pulsars at lower energies, which could be used as a prediction for future H.E.S.S. observations.

Lacroix et al. 2016 (preprint) - New H.E.S.S. diffuse emission from the Galactic center: a combination of heavy dark matter and millisecond pulsars? (arXiv)

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GAMMA-RAY EMISSION FROM THE SNR HB3

Image: At a distance of about 20,000 light years, G292.0+1.8 is one of only three supernova remnants in the Milky Way known to contain large amounts of oxygen. These oxygen-rich supernovas are of great interest to astronomers because they are one of the primary sources of the heavy elements (that is, everything other than hydrogen and helium) necessary to form planets and people. The X-ray image from Chandra shows a rapidly expanding, intricately structured, debris field that contains, along with oxygen (yellow and orange), other elements such as magnesium (green) and silicon and sulfur (blue) that were forged in the star before it exploded. Credit: NASA/CXC/SAO The processes of particles acceleration to very high energies from the supernova shock region and diffusion in the interstellar medium of such particles has not been well understood so far. Gamma-ray observations in the GeV regime are a powerful probe of these mechanisms

THE HITCHCHIKER'S GUIDE TO THE LOCAL SUPERCLUSTER

Image: Virgo Supercluster. Credit: Andrew Z. Colvin The Virgo Supercluster is a region with a diameter of 33 megaparsecs (~1000 times larger the Milky Way's diameter) containing at least 100 galaxy groups and clusters.

ORBITAL PERIODS OF THE PLANETS

For orbital period generally we refer to the sidereal period, that is the temporal cycle that it takes an object to make a full orbit, relative to the stars. This is the orbital period in an inertial (non-rotating) frame of reference (365,25 days for the earth).

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