SPI on INTEGRAL has provided spectra and a map of the sky in the emission from annihilations of positrons in the interstellar medium of our Galaxy. From high-resolution spectra we learned that a warm, partially-ionized medium is the site where the observed gamma-rays originate. The gamma-ray emission map shows a major puzzle for broader astrophysics topics, as it is dominated by a bright and extended apparently spherical emission region centered in the Galaxy's center. Only recently has the disk of the Galaxy been detected with SPI. This may be regarded as confirmation of earlier expectations that positrons should arise predominantly from sources of nucleosynthesis distributed throughout the plane of the Galaxy, which produce proton-rich unstable isotopes. But there are other plausible sources of positrons, among them pulsars and accreting binaries such as microquasars. SPI results may be interpreted also as hints that these are more significant as positron sources on the Galactic scale than thought before, in the plane and therefore also in the bulge of the Galaxy. This is part of the attempt to understand the surprisingly-bright emission from the central region in the Galaxy, which otherwise also could be interpreted as a first rather direct detection of dark matter annihilations in the Galaxy's gravitational well. INTEGRAL has a unique potential to shed light on the various aspects of positron astrophysics, through its capability for imaging spectroscopy.
Electron-positron Annihilation Lines and Decaying Sterile Neutrinos
如果存在大量的惰性中微子，它们衰变为光子和/或电子-正电子对可能会引起可观察到的后果。我们考虑了MeV无菌中微子衰变导致银河系中心弥散正电子湮没线的可能性，并由此从相关的天体物理/宇宙学数据中得到了无菌中微子衰变率$Γ_e \ge 10^{-28}$ s $^{-1}$的界.此外，我们预计软伽马流量$1.2 \times 10^{-4}-9.7 \times 10^{-4}$ ph cm $^{-2}$ s $^{-1}$从银河系中心，显示为一个小MeV的颠簸在背景光子谱。此外，我们还估计了无菌中微子衰变产生的活动中微子穿过地球的通量为$0.02-0.1$ cm $^{-2}$ s $^{-1}$。
The annihilation of positrons in the Milky Way galaxy has been observed for $\sim 50$ years however the production sites of these positrons remains hard to identify. The observed morphology of positron annihilation gamma-rays provides information on the annihilation sites of these Galactic positrons. It is understood that the positrons responsible for the annihilation signal originate at MeV energies. The majority of sources of MeV positrons occupy the thin, star forming disk of the Milky Way. If positrons propagate far from their sources, we must develop accurate models of positron propagatio…
We explore for the first time effects of the magnetic field on the escape of $^{22}$Na positrons and on the flux evolution of annihilation 511 keV line in novae. It is shown that for the white dwarf magnetic field of $\sim 10^6$ G the field of the expanding nova shell is able to significantly impede positrons escape and increase the time of the nova emission in 511keV up to hundreds days.
Observations of soft gamma rays emanating from the Milky Way from SPI/\textit{INTEGRAL} reveal the annihilation of $\sim2\times10^{43}$ positrons every second in the Galactic bulge. The origin of these positrons, which annihilate to produce a prominent emission line centered at 511 keV, has remained mysterious since their discovery almost 50 years ago. A plausible origin for the positrons is in association with the intense star formation ongoing in the Galactic center. Moreover, there is strong evidence for a nuclear outflow in the Milky Way. We find that advective transport and subsequent ann…
Hydrodynamic and kinetic models for spin-1/2 electron-positron quantum plasmas: Annihilation interaction, helicity conservation, and wave dispersion in magnetized plasmas
We revisit the properties of positron cloud in quark nugget (QN) model of dark matter (DM). In this model, dark matter particles are represented by compact composite objects composed of a large number of quarks or antiquarks with total baryon number $B\sim 10^{24}$. These particles have a very small number density in our galaxy which makes them "dark" to all DM detection experiments and cosmological observations. In this scenario, anti-quark nuggets play special role because they may manifest themselves in annihilation with visible matter. We study electron-positron annihilation in collisions …
Precision measurements of the positron flux in cosmic ray have revealed an unexplained bump in the spectrum around $E\simeq 300\,\mathrm{GeV}$, not clearly attributable to known astrophysical processes. We propose annihilation of dark matter of mass $m_χ= 780\,\mathrm{GeV}$ with a late-time cross section $σv = 4.63\times 10^{-24}\,\mathrm{cm^3\,s^{-1}}$ as a possible source. The nonmonotonic dependence of the annihilation rate on dark matter velocity, owing to a selective $p$-wave Sommerfeld enhancement, allows such a large signal from the Milky Way without violating corresponding constraints …
