MILLISECOND PULSAR ORIGIN OF THE GALACTIC CENTER GEV EXCESS

Image: The Milky Way. Credit: Serge Brunier

Using γ-ray data from the Fermi Large Area Telescope, various groups have identified a clear excess emission in the inner Galaxy, at energies around a few GeV. This excess attracted great attention, because it has properties typical for a dark matter annihilation signal.

Proposed diffuse emission mechanisms, like leptonic or hadronic outbursts or cosmic-ray injection in the central molecular zone, potentially explain part of the excess emission. However, it is challenging to explain all of the above aspects of the GCE with these mechanisms alone.

The most plausible astrophysical interpretation for the Galactic center eccess (GCE) is the combined emission from a large number of unresolved millisecond pulsars (MSPs) in the Galactic bulge region. Recently, it was shown that the spatial distribution of MSPs that were spilled out of disrupted globular clusters can explain the morphology of the GCE.

Image: SNR of the wavelet transform
of γ-rays with energies in the range 1-4 GeV.
Credit: Bartels et al. 2016

In a rencent paper (Bartels et al. 2016), using almost seven years of Fermi-LAT data, the authors detect a clustering of photons as predicted for the hypothetical population of millisecond pulsar, with a statistical significance of 10,8 σ. For plausible values of the luminosity function, this population explains 100% of the observed excess emission.

The authors argue that other extragalactic or Galactic sources, a mismodeling of Galactic diffuse emission, or the thick-disk population of pulsars are unlikely to account for this observation.

The paper (Bartels et. al 2016) is available online and is published in the PhRvL >>
http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.116.051102
http://arxiv.org/pdf/1506.05104v2.pdf

Comments

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).

A Sapphire Super-Earth

Twenty-one light years away, in the constellation Cassiopeia, a planet by the name of HD219134 b orbits its star with a year that is just three days long. With a mass almost five times that of Earth, it is what is known as a super-Earth. Unlike our planet, however, these super-Earths were formed at high temperatures close to their host star and contain high quantities of calcium, aluminum and their oxides – including sapphire and ruby. HD219134 b is one of three candidates likely to belong to a new, exotic class of exoplanets. These objects are completely different from the majority of Earth-like planets. They have 10 to 20 percent lower densities than Earth. Researchers looked at different scenarios to explain the observed densities. For example, a thick atmosphere could lead to a lower overall density. But two of the exoplanets studied, 55 Cancri e and WASP-47 e, orbit their star so closely that their surface temperature is almost 3,000 degrees and they would have lost this ...

Hubble observes energetic lightshow at Saturn’s north pole

This image is a composite of observations made of Saturn in early 2018 in the optical and of the auroras on Saturn’s north pole region, made in 2017. In contrast to the auroras on Earth the auroras on Saturn are only visible in the ultraviolet — a part of the electromagnetic spectrum blocked by Earth’s atmosphere — and therefore astronomers have to rely on space telescopes like the NASA/ESA Hubble Space Telescope to study them. Credit: ESA/Hubble, NASA, A. Simon (GSFC) and the OPAL Team, J. DePasquale (STScI), L. Lamy (Observatoire de Paris) In 2017, over a period of seven months, the NASA/ESA Hubble Space Telescope took images of auroras above Saturn’s north pole region using the Space Telescope Imaging Spectrograph. The observations were taken before and after the Saturnian northern summer solstice. These conditions provided the best achievable viewing of the northern auroral region for Hubble. On Earth, auroras are mainly created by particles or...

SpaceTime

Search This Blog