Radiation astronomy/Beta particles
A number of subatomic reactions can be detected in astronomy that yield beta particles. The detection of beta particles or the reactions that include them in an astronomical situation is beta-particles astronomy.
Notation: let TGF stand for a Terrestrial Gamma-ray Flash.
A "clumpiness in the [galactic] halo [is] through a spatially continuous elevation in the density of dark matter, rather than the more realistic discrete distribution of clumps. [...] the former approach reproduces the average results obtained when considering the essentially infinite set of possible configurations of discrete clumps within the halo. This was demonstrated in the work by Lavalle et al. (2006), who deduced that the associated relative variance in the observed positron flux, as a result of the different clump configurations, is proportional to , where is the typical clump mass, and diverges as Ee+ → mχ . It is found that for and a universal clump boost factor, Bc ∼ 100, this relative variance is less than 5 per cent for Ee+ ≤ 20 GeV, which is where the positron excess observed by the [High-Energy Antimatter Telescope] HEAT is located. Since the clump mass distribution deduced by Diemand et al. indicates that Mc ∼ 10−6M⊙, it seems very unlikely that such a variance will significantly affect our conclusions, and we use this to strengthen our use of a spatially continuous elevation in dark matter density as a way of acknowledging clumpiness in the galactic halo.
Although electron astronomy is usually not recognized as a formal branch of astronomy, the measurement of electron fluxes helps to understand a variety of natural phenomena.
""[E]lectron astronomy" has an interesting future".
"Positron astronomy is 30 years old but remains in its infancy."
A High-Energy Antimatter Telescope (HEAT) has been developed and tested in the mid 1990s to measure the positron fraction in cosmic rays.
Beta particles are high-energy, high-speed electrons or positrons emitted by certain types of radioactive nuclei such as potassium-40. The beta particles emitted are a form of ionizing radiation also known as beta rays. The production of beta particles is termed beta decay. They are designated by the Greek letter beta (β).
At right is a graph or block diagram that shows the boundaries for nuclear particle stability. The boundaries are conceptualized as drip lines. The nuclear landscape is understood by plotting boxes, each of which represents a unique nuclear species, on a graph with the number of neutrons increasing on the abscissa and number of protons increasing along the ordinate, which is commonly referred to as the table of nuclides, being to nuclear physics what the more commonly known periodic table of the elements is to chemistry. However, an arbitrary combination of protons and neutrons does not necessarily yield a stable nucleus, and ultimately when continuing to add more of the same type of nucleons to a given nucleus, the newly formed nucleus will essentially undergo immediate decay where a nucleon of the same isospin quantum number (proton or neutron) is emitted; colloquially the nucleon has 'leaked' or 'dripped' out of the target nucleus, hence giving rise to the term "drip line". The nucleons drip out of such unstable nuclei for the same reason that water drips from a leaking faucet: the droplet, or nucleon in this case, sees a lower potential which is great enough to overcome surface tension in the case of water droplets, and the strong nuclear force in the case of proton emission or alpha decay. As nucleons are quantized, then only integer values are plotted on the table of isotopes, indicating that the drip line is not linear but instead looks like a step function up close.
Beta particles (electrons) are more penetrating [than alpha particles], but still can be absorbed by a few millimeters of aluminum. However, in cases where high energy beta particles are emitted shielding must be accomplished with low density materials, e.g. plastic, wood, water or acrylic glass (Plexiglas, Lucite). This is to reduce generation of Bremsstrahlung X-rays. In the case of beta+ radiation (positrons), the gamma radiation from the electron-positron annihilation reaction poses additional concern.
As an example, "[t]he power into the Crab Nebula is apparently supplied by an outflow [wind] of ~1038 erg/s from the pulsar" where there are "electrons (and positrons) in such a wind". These beta particles coming out of the pulsar are moving very close to light speed.
"The two conversions of protons into neutrons are assumed to take place inside the nucleus, and the extra positive charge is emitted as a positron."
Def. "the non-linear scattering of radiation off electrons" is called induced Compton scattering.
"The effect of scattering is to move photons to lower frequencies." "[T]he fact that the radio pulses [from a pulsar] are not suppressed by induced scattering suggests that the wind's Lorentz factor exceeds ~104.
The electron is a subatomic particle with a negative charge, equal to -1.60217646x10-19 C. Current, or the rate of flow of charge, is defined such that one coulomb, so 1/-1.60217646x10-19, or 6.24150974x1018 electrons flowing past a point per second give a current of one ampere. The charge on an electron is often given as -e. note that charge is always considered positive, so the charge of an electron is always negative.
The electron has a mass of 9.10938188x10-31 kg, or about 1/1840 that of a proton. The mass of an electron is often written as me.
When working, these values can usually be safely approximated to:
- -e = -1.60x10-19 C
- me = 9.11x10-31kg
It has no known components or substructure; in other words, it is generally thought to be an elementary particle. The intrinsic angular momentum (spin) of the electron is a half-integer value in units of ħ, which means that it is a fermion.
A delta ray is characterized by very fast electrons produced in quantity by alpha particles or other fast energetic charged particles knocking orbiting electrons out of atoms. Collectively, these electrons are defined as delta radiation when they have sufficient energy to ionize further atoms through subsequent interactions on their own.
"The conventional procedure of delta-ray counting to measure charge (Powell, Fowler, and Perkins 1959), which was limited to resolution sigmaz = 1-2 because of uncertainties of the criterion of delta-ray ranges, has been significantly improved by the application of delta-ray range distribution measurements for 16O and 32S data of 200 GeV per nucleon (Takahashi 1988; Parnell et al. 1989)." Here, the delta-ray tracks in emulsion chambers have been used for "[d]irect measurements of cosmic-ray nuclei above 1 TeV/nucleon ... in a series of balloon-borne experiments".
Epsilon radiation is tertiary radiation caused by secondary radiation (e.g., delta radiation). Epsilon rays are a form of particle radiation and are composed of electrons. The term is very rarely used today.
Def. an elementary subatomic particle which forms matter is called a quark.
Note: quarks are never found alone in nature.
Def. the smallest possible, and therefore indivisible, unit of a given quantity or quantifiable phenomenon is called the quantum.
Def. one of certain integers or half-integers that specify the state of a quantum mechanical system is called a quantum number.
Def. a quantum number that depends upon the relative number of strange quarks and anti-strange quarks is called strangeness.
Def. symmetry of interactions under spatial inversion is called parity.
Def. a quantum number which determines the electromagnetic interactions is called an electric charge.
Def. the mean duration of the life of someone or something is called the mean lifetime.
Def. a quantum angular momentum associated with subatomic particles, which also creates a magnetic moment is called a spin.
Def. the quantity of matter which a body contains, irrespective of its bulk or volume is called mass.
Def. a subatomic particle corresponding to another particle with the same mass, spin and mean lifetime but with charge, parity, strangeness and other quantum numbers flipped in sign is called an antiparticle.
Def. matter that is composed of antiparticles of those that constitute normal matter is called antimatter.
A positron differs from a quark by its lack of strong interaction.
where A = 22, Z = 11, N = Na, Z-1 = 10, and N' = Ne.
Beta decay does not change the number of nucleons, A, in the nucleus but changes only its charge, Z. Thus the set of all nuclides with the same A can be introduced; these isobaric nuclides may turn into each other via beta decay. Among them, several nuclides (at least one) are beta stable, because they present local minima of the mass excess: if such a nucleus has (A, Z) numbers, the neighbour nuclei (A, Z−1) and (A, Z+1) have higher mass excess and can beta decay into (A, Z), but not vice versa. For all odd mass numbers A the global minimum is also the unique local minimum. For even A, there are up to three different beta-stable isobars experimentally known. There are about 355 known beta-decay stable nuclides total.
decay, or "positron emission", the weak interaction converts a nucleus into its next-lower neighbor on the periodic table while emitting an positron (e+
) and an electron neutrino (ν
decay cannot occur in an isolated proton because it requires energy due to the mass of the neutron being greater than the mass of the proton. β+
decay can only happen inside nuclei when the value of the binding energy of the mother nucleus is less than that of the daughter nucleus. The difference between these energies goes into the reaction of converting a proton into a neutron, a positron and a neutrino and into the kinetic energy of these particles.
Isotopes which undergo this decay and thereby emit positrons include carbon-11, potassium-40, nitrogen-13, oxygen-15, fluorine-18, and iodine-121. As an example, the following equation describes the beta plus decay of carbon-11 to boron-11, emitting a positron and a neutrino:
Def. an exotic atom consisting of a positron and an electron, but having no nucleus or an onium consisting of a positron (anti-electron) and an electron, as a particle–anti-particle bound pair is called positronium.
Being unstable, the two particles annihilate each other to produce two gamma ray photons after an average lifetime of 125 ps or three gamma ray photons after 142 ns in vacuum, depending on the relative spin states of the positron and electron.
The singlet state with antiparallel spins ([spin quantum number] S = 0, Ms = 0) is known as para-positronium (p-Ps) and denoted 1
0. It has a mean lifetime of 125 picoseconds and decays preferentially into two gamma quanta with energy of 511 keV each (in the center of mass frame). Detection of these photons allows for the reconstruction of the vertex of the decay. Para-positronium can decay into any even number of photons (2, 4, 6, ...), but the probability quickly decreases as the number increases: the branching ratio for decay into 4 photons is 1.439(2)×10−6
para-positronium lifetime (S = 0):
The triplet state with parallel spins (S = 1, Ms = −1, 0, 1) is known as ortho-positronium (o-Ps) and denoted 3S1. The triplet state in vacuum has a mean lifetime of 142.05±0.02 ns and the leading mode of decay is three gamma quanta. Other modes of decay are negligible; for instance, the five photons mode has branching ratio of ~1.0×10−6
ortho-positronium lifetime (S = 1):
The positron or antielectron is the antiparticle or the antimatter counterpart of the electron. The positron has an electric charge of +1e, a spin of ½, and has the same mass as an electron. When a low-energy positron collides with a low-energy electron, annihilation occurs, resulting in the production of two or more gamma ray photons.
The figure at right shows a positron (e+) emitted from an atomic nucleus together with a neutrino (v). Subsequently, the positron moves randomly through the surrounding matter where it hits several different electrons (e-) until it finally loses enough energy that it interacts with a single electron. This process is called an "annihilation" and results in two diametrically emitted photons with a typical energy of 511 keV each. Under normal circumstances the photons are not emitted exactly diametrically (180 degrees). This is due to the remaining energy of the positron having conservation of momentum.
Electron–positron annihilation occurs when an electron (e−
) and a positron (e+
, the electron's antiparticle) collide. The result of the collision is the annihilation of the electron and positron, and the creation of gamma ray photons or, at higher energies, other particles:
→ γ + γ
The process [does] satisfy a number of conservation laws, including:
- Conservation of electric charge. The net charge before and after is zero.
- Conservation of linear momentum and total energy. This forbids the creation of a single gamma ray. However, in quantum field theory this process is [described]; see examples of annihilation.
- Conservation of angular momentum.
As with any two charged objects, electrons and positrons may also interact with each other without annihilating, in general by elastic scattering.
The creation of only one photon can occur for tightly bound atomic electrons. In the most common case, two photons are created, each with energy equal to the rest energy of the electron or positron (511 keV). It is also common for three to be created, since in some angular momentum states, this is necessary to conserve C parity. Any larger number of photons [can be created], but the probability becomes lower with each additional photon. When either the electron or positron, or both, have appreciable kinetic energies, other heavier particles can also be produced (such as D mesons), since there is enough kinetic energy in the relative velocities to provide the rest energies of those particles. Photons and other light particles may be produced, but they will emerge with higher energies.
At energies near and beyond the mass of the carriers of the weak force, the W and Z bosons, the strength of the weak force becomes comparable with electromagnetism. It becomes much easier to produce particles such as neutrinos that interact only weakly.
Annihilation radiation is not monoenergetic, unlike gamma rays produced by radioactive decay. The production mechanism of annihilation radiation introduces Doppler broadening. The annihilation peak produced in a gamma spectrum by annihilation radiation therefore has a higher full width at half maximum (FWHM) than other gamma rays in [the] spectrum. The difference is more apparent with high resolution detectors, such as Germanium detectors, than with low resolution detectors such as Sodium iodide. Because of their well-defined energy (511 keV) and characteristic, Doppler-broadened shape, annihilation radiation can often be useful in defining the energy calibration of a gamma ray spectrum.
Two-photon physics, also called gamma-gamma physics, [studies] the interactions between two photons. If the energy in the center of mass system of the two photons is large enough, matter can be created.
- γ → e−
In nuclear physics, [the above reaction] occurs when a high-energy photon interacts with a nucleus. The photon must have enough energy [> 2*511 keV, or 1.022 MeV] to create an electron plus a positron. Without a nucleus to absorb momentum, a photon decaying into electron-positron pair (or other pairs for that matter such as a muon and anti-muon or a tau and anti-tau can never conserve energy and momentum simultaneously.
These interactions were first observed in Patrick Blackett's counter-controlled cloud chamber. In 2008 the Titan laser aimed at a 1-millimeter-thick gold target was used to generate positron–electron pairs in large numbers. "The LLNL scientists created the positrons by shooting the lab's high-powered Titan laser onto a one-millimeter-thick piece of gold."
Notation: WN5 is a component of V444 Cygni, with its Wolf-Rayet (W) spectrum dominated by NitrogenIII-V and HeliumI-II lines and WN2 to WN5 considered hotter or "early".
"The color temperature of the central part of the WN5 disk for λ < 7512 Å, where the main source of opacity is electron scattering, is Tc = 80,000-100,000 K. This high temperature represents the electron temperature slightly below the surface of the WN5 core--the level at which the star becomes optically thick in electron scattering."
Many samples of fluorite exhibit fluorescence under ultraviolet light, a property that takes its name from fluorite. Many minerals, as well as other substances, fluoresce. Fluorescence involves the elevation of electron energy levels by quanta of ultraviolet light, followed by the progressive falling back of the electrons into their previous energy state, releasing quanta of visible light in the process. In fluorite, the visible light emitted is most commonly blue, but red, purple, yellow, green and white also occur. The fluorescence of fluorite may be due to mineral impurities such as yttrium, ytterbium, or organic matter in the crystal lattice. In particular, the blue fluorescence seen in fluorites from certain parts of Great Britain responsible for the naming of the phenomenon of fluorescence itself, has been attributed to the presence of inclusions of divalent europium in the crystal.
Excessive "26Mg [has] been reported in meteoritic carbonaceous chondrites [...] which demonstrate an excess of 26Mg of up to 40% combined with essentially solar concentrations of 24Mg and 25Mg. Many of the data are well correlated with the 27Al content of the samples, and this is interpreted as evidence that the excess 26Mg has arisen from the in situ decay (via positron emission and electron capture) of the ground state of 26Al in these minerals."
Theoretical beta-particle astronomyEdit
"We now assume that the γ-rays are produced [from 3C 279] by relativistic electrons via Compton scattering of synchrotron photons (SSC). In any such model, the fact that the γ-rays luminosity, produced via Compton scattering, is higher than that emitted at lower frequencies (1014 - 1016 Hz), supposedly via the synchrotron process, implies a radiation energy density, Ur, higher than the magnetic energy density, UB. From the observed power ratio we derive that Ur must be one order of magnitude greater than UB, which may be a lower limit if Klein-Nishina effects reduce the efficiency of the self-Compton emission. This result is independent of the degree of beaming, which, for a homogeneous source, affects both the synchrotron and the self-Compton fluxes in the same way. This source is therefore the first observed case of the result of a Compton catastrophe (Hoyle, Burbidge, & Sargent 1966)."
Notation: let the symbol Ps stand for positronium.
"Comparison between direct annihilation and radiative capture to positronium [in thermal plasmas] shows that the two rates are equal at T = 6.8 x 105 K with the former (latter) dominating at the higher (lower) temperatures."
has a related mechanism in atomic hydrogen:
There may be a "connection ... between the magnetic field strengths inside an electron, in newly-born pulsars, and the sun. ... the upper limit to the strength of magnetic field ... is that which would permit emission of a photon at the non-relativistic electron gyrofrequency, with the energy of the order of the electron rest mass."
A "basic process in the formation of pulsar magnetic fields [may be] a variant of electron-positron spin-zero annihilation, as follows
where the [up] arrow represents the magnetic moment of an electron.
This relation "symbolises the formation of a magnetic entity, , here called an M-particle, with twice the magnetic moment of an electron or a positron, and [γ] represents a photon."
Low-mass X-ray binaries (LMXBs) "have long been suggested as positron sources on theoretical grounds and because their distribution peaks in the bulge region (eg Prantzos, 2004); however, it is only those LMXBs detected at hard X-ray energies that in addition exhibit an imbalance in their disk distribution."
"It is possible that the X-ray continuum is primary while the radio and optical emission are secondary for all BL Lac objects when the effect of relativistic beaming is considered. Pair production is a possible mechanism for producing X-ray emissions, while the optical and radio emission would be a consequence of this model (Zdziarski & Lightman 1985; Svensson 1986; Fabian et al. 1986). Barr & Mushotzky (1986) showed a significant correlation between the X-ray luminosity and timescale of X-ray variability for Seyfert galaxies and quasars and interpreted this as evidence that the emitting plasma is near the limit of being dominated by electron-positron pairs."
"The idea behind baryon matter is that a macroscopic state may exist in which a smaller effective baryon mass inside some region makes the state energetically favored over free particles. [...] This state will appear in the limit of large baryon number as an electrically neutral coherent bound state of neutrons, protons, and electrons in β-decay equilibrium."
"Energy deposit or escape is a major issue in expanding envelopes of stellar explosions, supernovae (positrons from 56Co and 44Ti) and novae (many β+ decays such as 13N)".
The X-ray continuum can arise from bremsstrahlung, black-body radiation, synchrotron radiation, or what is called inverse Compton scattering of lower-energy photons by relativistic electrons, knock-on collisions of fast protons with atomic electrons, and atomic recombination, with or without additional electron transitions.
"The annihilation of positrons with electrons gives rise to two spectral features, a line emission at 511 keV and a positronium continuum emission (which increases in intensity with energy roughly as a power law up to 511 keV and falls abruptly to zero above 511 keV)."
Notation: let the symbol LAT represent Large Area Telescope.
Notation: let the symbol GBM represent Gamma-ray Burst Monitor.
"The observed correlated variability of the GBM and LAT emissions indicates that photons formed co-spatially, with the lower-energy (GBM) photons providing target photons that can interact with higher energy γ rays to produce electron-positron pairs."
"[M]odels in which γ-rays are absorbed in collisions with X-rays producing nonthermal electron-positron pairs, which in turn radiate further X-rays [have been developed]."
"[T]he reprocessing of radiation by e+ e- pairs could be a sufficiently robust mechanism to yield the canonical spectrum, independent of the details of the particle acceleration mechanism and the parameters of the source, such as the X- and γ-ray luminosity, L, and the size, R."
"[T]he hard X-ray spectrum of a growing number of [active galactic nuclei] AGN [in] the 1-30 keV X-ray emission has four distinct components":
- "an incident power law spectrum with a spectral index αix ≃ 0.9,"
- "an emission line at the energy ~6.4 keV (interpreted as a fluorescent iron K-line),"
- "an absorption edge at 7-8 keV (interpreted as an iron K-edge), and"
- "a broad excess of emission with respect to the underlying power law at energies ≳ 10 keV (interpreted as Compton reflection from cold [T < 106 K, optically thick] material)." 
"For sources located in the field of view, the data obtained during an exposure (pointing) p, for a given energy band, can be expressed by the relation:"
"where is the response of the instrument for the source j, is the flux of the source j, and is the background recorded during the pointing p. , and are vectors of 19 elements."
"[I]n the 508.25-513.75 keV band ... a 5.5 keV wide band centered at 511 keV takes into account the Germanium energy resolution (FWHM 2.05 keV) including its degradation between two consecutive annealings (5%). At this energy, the gain calibration (performed orbit-wise) accuracy is better than ±0.01 keV."
"[Taking] advantage of the relative stability of the background pattern to rewrite the background term as:"
"where is a normalization coefficient per pointing, is the "uniformity map" or background count rate pattern on the SPI camera [of the INTEGRAL satellite] and the effective observation time for pointing p. and are vectors of 19 elements (one per detector)."
"The main physical processes at play are the emission of γ-rays and positrons from radioactive decays in the 56Ni → 56Co → 56Fe chain [...], their interaction with the ejecta, and the spectrum of the radiation produced by the thermalization processes and the radiative transfer in the expanding ejecta. [...] Positron interaction with the ejecta [from the Type Ic SN 1994I] strongly depends on the presence, and geometry, of magnetic fields (Ruiz-Lapuente & Spruit 1998)."
Aluminium-26, 26Al, is a radioactive isotope of the chemical element aluminium, decaying by either of the modes beta-plus or electron capture, both resulting in the stable nuclide magnesium-26. The half-life of 26Al is 7.17×105 years. This is far too short for the isotope to survive to the present, but a small amount of the nuclide is produced by collisions of argon atoms with cosmic ray protons.
There is an "unexpected rise of the positron fraction, observed by HEAT and PAMELA experiments, for energies larger than a few GeVs."
"[T]he HEAT balloon experiment  ... has mildly indicated a possible positron excess at energies larger than 10 GeV ... In October 2008, the latest results of PAMELA experiment  have confirmed and extended this feature ."
Earlier measurements indicate that "the positron fraction, [f = ] e+/(e- + e+), increases with energy at energies above 10 GeV. Such an increase would require either the appearance of a new source of positrons or a depletion of primary electrons." All results taken together suggest a slight decrease with increasing energy from about 1 GeV to 10 GeV, but overall the fraction may be constant, per Figure 2.
"The positrons can annihilate in flight before being slowed to thermal energies, annihilate directly with electrons when both are at thermal energies, or form positronium at thermal energies (or at greater than thermal energies if positronium formation occurs via charge exchange with neutrals)."
"Few exceptional lines arise at high energy from annihilations of positrons and pions."
"Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) hard X-ray (HXR) and γ-ray imaging and spectroscopy observations [were made] of the intense (X4.8) γ-ray line flare of 2002 July 23."
"For the first time, the positron annihilation line is resolved, and the detailed high-resolution measurements are obtained for the neutron-capture line. The first ever solar γ-ray line and continuum imaging shows that the source locations for the relativistic electron bremsstrahlung overlap the 50-100 keV HXR sources, implying that electrons of all energies are accelerated in the same region. The centroid of the ion-produced 2.223 MeV neutron-capture line emission, however, is located ~20 ± 6 away, implying that the acceleration and/or propagation of the ions must differ from that of the electrons. Assuming that Coulomb collisions dominate the energetic electron and ion energy losses (thick target), we estimate that a minimum of ~2 × 1031 ergs is released in accelerated >~20 keV electrons during the rise phase, with ~1031 ergs in ions above 2.5 MeV nucleon-1 and about the same in electrons above 30 keV released in the impulsive phase."
"The collisions also produce neutrons, positrons, and pions. Neutron capture on hydrogen and positron annihilation yield narrow lines at 2.223 and 0.511 MeV, respectively, both of which are delayed."
Based on interactions between cosmic rays and the photons of the cosmic microwave background radiation (CMB), cosmic rays with energies over the threshold energy of 5x1019 eV interact with cosmic microwave background photons to produce pions via the resonance,
Pions produced in this manner proceed to decay in the standard pion channels—ultimately to photons for neutral pions, and photons, positrons, and various neutrinos for positive pions. Neutrons decay also to similar products, so that ultimately the energy of any cosmic ray proton is drained off by production of high energy photons plus (in some cases) high energy electron/positron pairs and neutrino pairs.
The pion production process begins at a higher energy than ordinary electron-positron pair production (lepton production) from protons impacting the CMB, which starts at cosmic ray proton energies of only about 1017eV. However, pion production events drain 20% of the energy of a cosmic ray proton as compared with only 0.1% of its energy for electron positron pair production. This factor of 200 is from two sources: the pion has only about ~130 times the mass of the leptons, but the extra energy appears as different kinetic energies of the pion or leptons, and results in relatively more kinetic energy transferred to a heavier product pion, in order to conserve momentum. The much larger total energy losses from pion production result in the pion production process becoming the limiting one to high energy cosmic ray travel, rather than the lower-energy light-lepton production process.
"TeV muons from γ ray primaries ... are rare because they are only produced by higher energy γ rays whose flux is suppressed by the decreasing flux at the source and by absorption on interstellar light."
Muon decay produces three particles, an electron plus two neutrinos of different types.
"The muons created through decays of secondary pions and kaons are fully polarized, which results in electron/positron decay asymmetry, which in turn causes a difference in their production spectra."
The following fusion reaction produces neutrinos and accompanying gamma-rays of the energy indicated:
Observation of gamma rays of this energy likely indicate this reaction is occurring nearby.
e + p+
The positron quickly finds an electron, and they annihilate each other. The two resulting gamma rays (γ) 511 keV each are detectable. The neutron can be detected by its capture on an appropriate nucleus, releasing a gamma ray. The coincidence of both events – positron annihilation and neutron capture – gives a unique signature of an antineutrino interaction.
Most astronomical gamma-rays may be produced from the same type of accelerations of electrons, and electron-photon interactions, that produce X-rays in astronomy (but occurring at a higher energy in the production of gamma-rays).
The correlations of the high energy electrons energized during a solar flare and the gamma rays [produced] are mostly caused by nuclear combinations of high energy protons and other heavier ions.
"The Energetic Gamma Ray Experiment Telescope, (EGRET) measured high energy (20 MeV to 30 GeV) gamma ray source positions to a fraction of a degree and photon energy to within 15 percent. EGRET was developed by NASA Goddard Space Flight Center, the Max Planck Institute for Extraterrestrial Physics, and Stanford University. Its detector operated on the principle of electron-positron pair production from high energy photons interacting in the detector. The tracks of the high-energy electron and positron created were measured within the detector volume,and the axis of the V of the two emerging particles projected to the sky. Finally, their total energy was measured in a large calorimeter scintillation detector at the rear of the instrument.
X-rays remove electrons from atoms and ions, and those photoelectrons can provoke secondary ionizations. As the intensity is often low, this [X-ray] heating is only efficient in warm, less dense atomic medium (as the column density is small). For example in molecular clouds only hard x-rays can penetrate and x-ray heating can be ignored. This is assuming the region is not near an x-ray source such as a supernova remnant.
In an X-ray tube, electrons are accelerated in a vacuum by an electric field and shot into a piece of metal called the "target". X-rays are emitted as the electrons slow down (decelerate) in the metal. The output spectrum consists of a continuous spectrum of X-rays, with additional sharp peaks at certain energies characteristic of the elements of the target.
The Energetic Gamma Ray Experiment Telescope, (EGRET) measured high energy (20 MeV to 30 GeV) gamma ray source positions to a fraction of a degree and photon energy to within 15 percent. EGRET was developed by NASA Goddard Space Flight Center, the Max Planck Institute for Extraterrestrial Physics, and Stanford University. Its detector operated on the principle of electron-positron pair production from high energy photons interacting in the detector. The tracks of the high-energy electron and positron created were measured within the detector volume,and the axis of the V of the two emerging particles projected to the sky. Finally, their total energy was measured in a large calorimeter scintillation detector at the rear of the instrument.
In "the spectrum of a middle-aged [pulsar] PSR B0656+14 [may be] two wide, red and blue, flux depressions whose frequency ratio is about 2 and which could be the 1st and 2nd harmonics of electron/positron cyclotron absorption formed at magnetic fields [of] ~108 G in [the] upper magnetosphere of the pulsar."
"The temperature of yellow coronal regions is ... about 2.5 [x] 106 [K]. ... although some ions Ca XV will exist at lower, as well as higher temperatures."
"The AS prominences [AS in Menzel-Evans' classification ;] move with velocities exceeding by far the velocities of other types of prominences , . As short-living phenomena, they are condensed quickly and the temperature of the coronal gases should rise in the early stages of their condensation. Indeed, the AS prominences use to be allied with yellow line emission (λ 5694)."
"The yellow line is namely due to the ion Ca XV, according to Edlen's and Waldmeier's identification. ... the line λ 5694 is emitted by 3P1 - 3P0 transition of Ca XV."
"The solar corona is not in thermodynamical equilibrium. In particular, the photo-recombination is compensated with electron impact ionization, while the reverse processes viz. the photoionization and recombination by impact with two electrons are there negligible."
In infrared astronomy, the cosmic infrared background (CIB) causes a significant attenuation for very high energy electrons through inverse Compton scattering, photopion and electron-positron pair production.
"Radio observations at 210 GHz taken by the Bernese Multibeam Radiometer for KOSMA (BEMRAK) [of] high-energy particle acceleration during the energetic solar flare of 2003 October 28 [...] at submillimeter wavelengths [reveal] a gradual, long-lasting (>30 minutes) component with large apparent source sizes (~60"). Its spectrum below ~200 GHz is consistent with synchrotron emission from flare-accelerated electrons producing hard X-ray and γ-ray bremsstrahlung assuming a magnetic field strength of ≥200 G in the radio source and a confinement time of the radio-emitting electrons in the source of less than 30 s. [... There is a] close correlation in time and space of radio emission with the production of pions".
There is a cut-off frequency above which the equation cannot be satisfied. Since the refractive index is a function of frequency (and hence wavelength), the intensity does not continue increasing at ever shorter wavelengths even for ultra-relativistic particles (where v/c approaches 1). At X-ray frequencies, the refractive index becomes less than unity (note that in media the phase velocity may exceed c without violating relativity) and hence no X-ray emission (or shorter wavelength emissions such as gamma rays) would be observed. However, X-rays can be generated at special frequencies just below those corresponding to core electronic transitions in a material, as the index of refraction is often greater than 1 just below a resonance frequency (see Kramers-Kronig relation and anomalous dispersion).
"Throughout the shower development, the electrons and positrons which travel faster than the speed of light in the air emit Cherenkov radiation."
"High energy processes such as Compton, Bhabha, and Moller scattering, along with positron annihilation rapidly lead to a ~20% negative charge asymmetry in the electron-photon part of a cascade ... initiated by a ... 100 PeV neutrino".
"The tachyonic spectral densities generated by ultra-relativistic electrons in uniform motion are fitted to the high-energy spectra of Galactic supernova remnants, such as RX J0852.0−4622 and the pulsar wind nebulae in G0.9+0.1 and MSH 15-52. ... Tachyonic cascade spectra are quite capable of generating the spectral curvature seen ... Estimates on the electron/proton populations generating the tachyon flux are obtained from the spectral fits"
"[S]uperluminal neutrinos may lose energy rapidly via the bremsstrahlung [Cherenkov radiation] of electron-positron pairs "
"muon neutrinos with energies of order tens of GeV travel at superluminal velocity."
For "all cases of superluminal propagation, certain otherwise forbidden processes are kinematically permitted, even in vacuum."
"These processes cause superluminal neutrinos to lose energy as they propagate and ... process (c) places a severe constraint upon potentially superluminal neutrino velocities. ... Process (c), pair bremsstrahlung, proceeds through the neutral current weak interaction."
"Throughout the shower development, the electrons and positrons which travel faster than the speed of light in the air emit Cherenkov radiation."
"Plasma is the fourth state of matter, consisting of electrons, ions and neutral atoms, usually at temperatures above 104 degrees Kelvin."
[P]lasma is a state of matter similar to gas in which a certain portion of the particles are ionized. Heating a gas may ionize its molecules or atoms (reduce or increase the number of electrons in them), thus turning it into a plasma, which contains charged particles: positive ions and negative electrons or ions.
For plasma to exist, ionization is necessary. The term "plasma density" by itself usually refers to the "electron density", that is, the number of free electrons per unit volume. The degree of ionization of a plasma is the proportion of atoms that have lost or gained electrons, and is controlled mostly by the temperature. Even a partially ionized gas in which as little as 1% of the particles are ionized can have the characteristics of a plasma (i.e., response to magnetic fields and high electrical conductivity). The degree of ionization, α is defined as α = ni/(ni + na) where ni is the number density of ions and na is the number density of neutral atoms. The electron density is related to this by the average charge state <Z> of the ions through ne = <Z> ni where ne is the number density of electrons.
Above the photosphere visible sunlight is free to propagate into space, and its energy escapes the Sun entirely. The change in opacity is due to the decreasing amount of H− ions, which absorb visible light easily. Conversely, the visible light we see is produced as electrons react with hydrogen atoms to produce H− ions. The photosphere has a particle density of ~1023 m−3 (this is about 0.37% of the particle number per volume of Earth's atmosphere at sea level; however, photosphere particles are electrons and protons, so the average particle in air is 58 times as heavy).
"Positrons entering a gaseous medium at [0.6 to 4.5 MeV] are quickly slowed by ionizing collisions with neutral atoms and by long-range Coulomb interactions with any ionized component."
"Even in small solids and dust grains, energy deposition from 26Al β-decay, for example, injects 0.355 W kg-1 of heat. This is sufficient to result in melting signatures, which have been used to study condensation sequences of solids in the early solar system".
"The major problems associated with the balloon borne positron measurements are (i) the unique identification against a vast background of protons, and (ii) corrections for the positrons produced in the residual atmosphere."
"[T]o account for the atmospheric corrections ... first [use] the instrument to determine the negative muon spectrum at float altitude. ... [Use this] spectrum ... to normalize the analytically determined atmospheric electron-positron spectra. ... most of the atmospheric electrons and positrons at small atmospheric depths are produced from muon decay at [the energies from 0.85 to 14 GeV]."
26Al "decays into excited 26Mg by either positron decay or electron capture. In both cases, the excited magnesium isotope de-excites radatively, releasing a photon of energy 1.809 MeV."
"The 26Al concentration in a meteorite depends upon different [parameters] like the exposure age, the shielding conditions of the analyzed sample and the terrestrial age of the meteorite."
"As 26Al is a positron emitting isotope, it is possible to measure 26Al in meteorites by gamma-coincidence low level counting techniques . Positron annihilation radiation (due to the destructive recombination of a positron and an electron) is emitted as two simultaneous 511 keV gamma rays with 180° angle correlation. By focusing exclusively on the coincident 511 keV events, a drastic reduction of the detected radiation background is achieved, and the non-destructive determination of 26Al in bulk samples of 5-50 g becomes possible."
The preflare solar material is observed "to be an elevated cloud of prominence-like material which is suddenly lit up by the onslaught of hard electrons accelerated in the flare; the acceleration may be inside or outside the cloud, and brightening is seen in other areas of the solar surface on the same magnetic field lines."
"The suprathermal electrons in the solar wind and in solar particle events have excellent properties for this application: they move rapidly, they remain tightly bound to their field lines, and they may arrive "scatter-free" even at low energies, and from deep in the solar atmosphere (Lin 1985)."
Helmet streamers are bright loop-like structures which develop over active regions on the sun. They are closed magnetic loops which connect regions of opposite magnetic polarity. Electrons are captured in these loops, and cause them to glow very brightly. The solar wind elongates these loops to pointy tips. They far extend above most prominences into the corona, and can be readily observed during a solar eclipse. Helmet streamers are usually confined to the "streamer belt" in the mid latitudes, and their distribution follows the movement of active regions during the solar cycle. Small blobs of plasma, or "plasmoids" are sometimes released from the tips of helmet streamers, and this is one source of the slow component of the solar wind. In contrast, formations with open magnetic field lines are called coronal holes, and these are darker and are a source of the fast solar wind. Helmet streamers can also create coronal mass ejections if a large volume of plasma becomes disconnected near the tip of the streamer.
In the corona thermal conduction occurs from the external hotter atmosphere towards the inner cooler layers. Responsible for the diffusion process of the heat are the electrons, which are much lighter than ions and move faster.
The solar flare at Active Region 10039 on July 23, 2002, exhibits many exceptional high-energy phenomena including the 2.223 MeV neutron capture line and the 511 keV electron-positron (antimatter) annihilation line. In the image at right, the RHESSI low-energy channels (12-25 keV) are represented in red and appear predominantly in coronal loops. The high-energy flux appears as blue at the footpoints of the coronal loops. Violet is used to indicate the location and relative intensity of the 2.2 MeV emission.
During solar flares “[s]everal radioactive nuclei that emit positrons are also produced; [which] slow down and annihilate in flight with the emission of two 511 keV photons or form positronium with the emission of either a three gamma continuum (each photon < 511 keV) or two 511 keV photons." The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) made the first high-resolution observation of the solar positron-electron annihilation line during the July 23, 2003 solar flare. The observations are somewhat consistent with electron-positron annihilation in a quiet solar atmosphere via positronium as well as during flares. Line-broadening is due to "the velocity of the positronium." "The width of the annihilation line is also consistent ... with thermal broadening (Gaussian width of 8.1 ± 1.1 keV) in a plasma at 4-7 x 105 K. ... The RHESSI and all but two of the SMM measurements are consistent with densities ≤ 1012 H cm-3 [but] <10% of the p and α interactions producing positrons occur at these low densities. ... positrons produced by 3He interactions form higher in the solar atmosphere ... all observations are consistent with densities > 1012 H cm-3. But such densities require formation of a substantial mass of atmosphere at transition region temperatures."
Particles such as electrons are used as tracers of cosmic magnetic fields.
"From a plasma-physics point of view, the particles represent the correct way to identify magnetic field lines." "The suprathermal electrons in the solar wind and in solar particle events have excellent properties for this application: they move rapidly, they remain tightly bound to their field lines, and they may arrive "scatter-free" even at low energies, and from deep in the solar atmosphere (Lin 1985)."
"Energetic photons, ions and electrons from the solar wind, together with galactic and extragalactic cosmic rays, constantly bombard surfaces of planets, planetary satellites, dust particles, comets and asteroids."
Mariner 10 has aboard "one backward facing electron spectrometer (BESA). ... An electron spectrum [is] obtained every 6 s, ... within the energy range 13.4-690 eV. ... [B]y taking into account [the angular] distortion [caused by the solar wind passing the spacecraft] and the spacecraft sheath characteristics ... some of the solar wind plasma parameters such as ion bulk speed, electron temperature, and electron density [are derived]." Mariner 10 had three encounters with Mercury on March 29, 1974, September 21, 1974, and on March 16, 1975. The BESA measurements "show that the planet interacts with the solar wind to form a bow shock and a permanent magnetosphere. ... The magnetosphere of Mercury appears to be similar in shape to that of the earth but much smaller in relation to the size of the planet. The average distance from the center of Mercury to the subsolar point of the magnetopause is ∼ 1.4 planetary radii. Electron populations similar to those found in the earth’s magnetotail, within the plasma sheet and adjacent regions, were observed at Mercury; both their spatial location and the electron energy spectra within them bear qualitative and quantitative resemblance to corresponding observations at the earth."
"[T]he Mercury encounter (M I) by Mariner 10 on 29 March 1974 occurred during the height of a Jovian electron increase in the interplanetary medium."
The first ever X-ray image of Venus is shown at right. The "half crescent is due to the relative orientation of the Sun, Earth and Venus. The X-rays from Venus are produced by fluorescent radiation from oxygen and other atoms in the atmosphere between 120 and 140 kilometers above the surface of the planet. In contrast, the optical light from Venus is caused by the reflection from clouds 50 to 70 kilometers above the surface. Solar X-rays bombard the atmosphere of Venus, knock electrons out of the inner parts of atoms, and excite the atoms to a higher energy level. The atoms almost immediately return to their lower energy state with the emission of a fluorescent X-ray. A similar process involving ultraviolet light produces the visible light from fluorescent lamps."
With respect to the rocky-object Earth, between the surface and various altitudes there is an electric field induced by the ionosphere. It changes with altitude from about 150 volts per meter at the suface to lower values at higher altitude. In fair weather, it is relatively constant, in turbulent weather it is accompanied by ions. At greater altitude these chemical species continue to increase in concentration. To dissipate the accumulation of greater charge differential between the surface and the ionosphere, the gases between suffer breakdown (ionization) that permits lightning to be either a draw of negative charge, usually electrons, upward from the surface or a transfer of positive charge to the ground.
"[L]ow-altitude regions of downward electric current on auroral magnetic field lines are sites of dramatic upward magnetic field-aligned electron acceleration that generates intense magnetic field-aligned electron beams within Earth’s equatorial middle magnetosphere."
The ionosphere is a shell of electrons and electrically charged atoms and molecules that surrounds the Earth, stretching from a height of about 50 km to more than 1000 km. It owes its existence primarily to ultraviolet radiation from the Sun.
The images [lower right] are superimposed on a simulated image of the Earth. The color code represents brightness, maximum in red. Distance from the North pole to the black circle is 3,340 km (2,080 mi).
"Auroras are produced by solar storms that eject clouds of energetic charged particles. These particles are deflected when they encounter the Earth’s magnetic field, but in the process large electric voltages are created. Electrons trapped in the Earth’s magnetic field are accelerated by these voltages and spiral along the magnetic field into the polar regions. There they collide with atoms high in the atmosphere and emit X-rays".
At right is a composite image which contains the first picture of the Earth in X-rays, taken in March, 1996, with the orbiting Polar satellite. The area of brightest X-ray emission is red.
Energetic charged particles from the Sun energize electrons in the Earth's magnetosphere. These electrons move along the Earth's magnetic field and eventually strike the ionosphere, causing the X-ray emission. Lightning strikes or bolts across the sky also emit X-rays.
“One approach for characterizing the sky distribution of positron annihilation radiation is to fit to the data parameterized (and idealized) model distributions, representing the Galactic bulge, halo, and disk.” “Two scenarios for the Galactic dsitribution of 511 keV line emission that remain viable after more than 4 years of observations with SPI [are]
- bulge + thick disk (BD) and
- halo + thin disk (HD).”
In 2009, the Fermi Gamma Ray Telescope in Earth orbit observed [an] intense burst of gamma rays corresponding to positron annihilations coming out of a storm formation. Scientists wouldn't have been surprised to see a few positrons accompanying any intense gamma ray burst, but the lightning flash detected by Fermi appeared to have produced about 100 trillion positrons. This has been reported by media in January 2011, it is an effect, never considered to happen before.
"The Gamma-ray Burst Monitor (GBM) detects sudden flares of gamma-rays produced by gamma ray bursts and solar flares. Its scintillators are on the sides of the spacecraft to view all of the sky which is not blocked by the earth. The design is optimized for good resolution in time and photon energy. The Gamma-ray Burst Monitor has detected gamma rays from positrons generated in powerful thunderstorms.
Van Allen radiation beltsEdit
The Van Allen radiation belt is split into two distinct belts, with energetic electrons forming the outer belt and a combination of protons and electrons forming the inner belts. In addition, the radiation belts contain lesser amounts of other nuclei, such as alpha particles.
The large outer radiation belt extends from an altitude of about three to ten Earth radii (RE) or 13,000 to 60,000 kilometres above the Earth's surface. Its greatest intensity is usually around 4–5 RE. The outer electron radiation belt is mostly produced by the inward radial diffusion and local acceleration due to transfer of energy from whistler mode plasma waves to radiation belt electrons. Radiation belt electrons are also constantly removed by collisions with atmospheric neutrals, losses to magnetopause, and the outward radial diffusion. The outer belt consists mainly of high energy (0.1–10 MeV) electrons trapped by the Earth's magnetosphere. The gyroradii for energetic protons would be large enough to bring them into contact with the Earth's atmosphere. The electrons here have a high flux and at the outer edge (close to the magnetopause), where geomagnetic field lines open into the geomagnetic "tail", fluxes of energetic electrons can drop to the low interplanetary levels within about 100 km (a decrease by a factor of 1,000).
The electron reflectometer (ER) aboard the Lunar Prospector determines the location and strength of magnetic fields from the energy spectrum and direction of electrons. The instrument measures the pitch angles of solar wind electrons reflected from the Moon by lunar magnetic fields. Stronger local magnetic fields can reflect electrons with larger pitch angles. Field strengths as small as 0.01 [nanotesla] nT could be measured with a spatial accuracy of about 3 km (1.9 mi) at the lunar surface.
"[T]he shadowed lunar surface charges negative."
"[L]uminescence dating techniques [may] provide absolute age determinations of eolian sediments on the surface of Mars, including those incorporated in the martian polar ice caps. Fundamental thermally and optically stimulated luminescence properties of bulk samples of JSC Mars-1 soil simulant [have been studied]. The radiation-induced luminescence signals (both thermoluminescence, TL, and optically stimulated luminescence, OSL) from JSC Mars-1 are found to have a wide dynamic dose–response range, with the luminescence increasing linearly to the highest doses used (936 Gy), following irradiation with 90Sr/90Y beta particles."
The image at right represents "[t]he Jovian magnetosphere [magnetic field lines in blue], including the Io flux tube [in green], Jovian aurorae, the sodium cloud [in yellow], and sulfur torus [in red]."
"Io may be considered to be a unipolar generator which develops an emf [electromotive force] of 7 x 105 volts across its radial diameter (as seen from a coordinate frame fixed to Jupiter)."
"This voltage difference is transmitted along the magnetic flux tube which passes through Io. ... The current [in the flux tube] must be carried by keV electrons which are electrostatically accelerated at Io and at the top of Jupiter's ionosphere."
"Io's high density (4.1 g cm-3) suggests a silicate composition. A reasonable guess for its electrical conductivity might be the conductivity of the Earth's upper mantle, 5 x 10-5 ohm-1 cm-1 (Bullard 1967)."
As "a conducting body [transverses] a magnetic field [it] produces an induced electric field. ... The Jupiter-Io system ... operates as a unipolar inductor" ... Such unipolar inductors may be driven by electrical power, develop hotspots, and the "source of heating [may be] sufficient to account for the observed X-ray luminosity".
"The electrical surroundings of Io provide another energy source which has been estimated to be comparable with that of the [gravitational] tides (7). A current of 5 x 106 A is ... shunted across flux tubes of the Jovian field by the presence of Io (7-9)."
"[W]hen the currents [through Io] are large enough to cause ohmic heating ... currents ... contract down to narrow paths which can be kept hot, and along which the conductivity is high. Tidal heating [ensures] that the interior of Io has a very low eletrical resistance, causing a negligible extra amount of heat to be deposited by this current. ... [T]he outermost layers, kept cool by radiation into space [present] a large resistance and [result in] a concentration of the current into hotspots ... rock resistivity [and] contact resistance ... contribute to generate high temperatures on the surface. [These are the] conditions of electric arcs [that can produce] temperatures up to ionization levels ... several thousand kelvins".
"[T]he outbursts ... seen [on the surface may also be] the result of the large current ... flowing in and out of the domain of Io ... Most current spots are likely to be volcanic calderas, either provided by tectonic events within Io or generated by the current heating itself. ... [A]s in any electric arc, very high temperatures are generated, and the locally evaporated materials ... are ... turned into gas hot enough to expand at a speed of 1 km/s."
"Field-aligned equatorial electron beams [have been] observed within Jupiter’s middle magnetosphere. ... the Jupiter equatorial electron beams are spatially and/or temporally structured (down to <20 km at auroral altitudes, or less than several minutes), with regions of intense beams intermixed with regions absent of such beams."
"Jovian electrons, both at Jupiter and in the interplanetary medium near Earth, have a very hard spectrum that varies as a power law with energy (see, e.g., Mewaldt et al. 1976). This spectral character is sufficiently distinct from the much softer solar and magnetospheric electron spectra that it has been used as a spectral filter to separate Jovian electrons from other sources ... A second Jovian electron characteristic is that such electrons in the interplanetary medium tend to consist of flux increases of several days duration which recur with 27 day periodicities ... A third feature of Jovian electrons at 1 AU is that the flux increases exhibit a long-term modulation of 13 months which is the synodic period of Jupiter as viewed from Earth".
Jovian electrons propagate "along the spiral magnetic field of the interplanetary medium [from Jupiter and its magnetosphere to the Sun]".
At right is a complete global color image of Callisto. Bright scars on a darker surface testify to a long history of impacts on Jupiter's moon Callisto. The picture, taken in May 2001, is the only complete global color image of Callisto obtained by Galileo, which has been orbiting Jupiter since December 1995. Of Jupiter's four largest moons, Callisto orbits farthest from the giant planet. Callisto's surface is uniformly cratered but is not uniform in color or brightness. Scientists believe the brighter areas are mainly ice and the darker areas are highly eroded, ice-poor material.
"[M]agnetospheric electron (bi-directional) beams connect to the expected locations of Saturn’s aurora".
Powered by the Saturnian equivalent of (filamentary) Birkeland currents, streams of charged particles from the interplanetary medium interact with the planet's magnetic field and funnel down to the poles. Double layers are associated with (filamentary) currents, and their electric fields accelerate ions and electrons.
These electrons "provide remote-sensing observations of distant targets in the heliosphere - the Sun, the Moon, Jupiter, and various heliospheric structures."
As of December 5, 2011, "Voyager 1 is about ... 18 billion kilometers ... from the [S]un [but] the direction of the magnetic field lines has not changed, indicating Voyager is still within the heliosphere ... the outward speed of the solar wind had diminished to zero in April 2010 ... inward pressure from interstellar space is compacting [the magnetic field] ... Voyager has detected a 100-fold increase in the intensity of high-energy electrons from elsewhere in the galaxy diffusing into our solar system from outside ... [while] the [solar] wind even blows back at us."
"In the first 18 months of operations, AMS-02 [image under Cherenkov detectors] recorded 6.8 million positron (an antimatter particle with the mass of an electron but a positive charge) and electron events produced from cosmic ray collisions with the interstellar medium in the energy range between 0.5 giga-electron volt (GeV) and 350 GeV. These events were used to determine the positron fraction, the ratio of positrons to the total number of electrons and positrons. Below 10 GeV, the positron fraction decreased with increasing energy, as expected. However, the positron fraction increased steadily from 10 GeV to 250 GeV. This increase, seen previously though less precisely by instruments such as the Payload for Matter/antimatter Exploration and Light-nuclei Astrophysics (PAMELA) and the Fermi Gamma-ray Space Telescope, conflicts with the predicted decrease of the positron fraction and indicates the existence of a currently unidentified source of positrons, such as pulsars or the annihilation of dark matter particles. Furthermore, researchers observed an unexpected decrease in slope from 20 GeV to 250 GeV. The measured positron to electron ratio is isotropic, the same in all directions."
"The day after its discovery by the Watch instrument, the X-ray nova GRS 1124-684 in Musca was detected by the soft γ-ray telescope SIGMA at the limit of its field of view. [...] an emission feature around 500 keV in the source spectrum during one postflare observation [...] is [the] first clear evidence of γ-ray line emission from soft X-ray transients, and, [is] interpreted as a positron annihilation line".
In "a 10 keV to 1 MeV X-ray spectrum of Cyg X-1 in its low state, accumulated over ≡3 months in 1977 and 1978. The spectrum is smooth up to 300 keV. The excess at higher energy may be interpreted as a broad 511 keV emission line from the annihilation of positrons."
On November 25, 1970, from Paraná, Argentina, latitude 32° S, "[a] balloon-altitude observation was conducted ... of the galactic-center region, at energies between 23 and 930 keV. ... evidence for a spectral feature at 0.5 MeV is [detected]." The radiation detected over about 300 to 103 keV fit a power law of
- N(E) = (10.5 ± 2.2) E-(2.37±0.05) photons cm-2 s-1 keV-1.
The 0.5 MeV peak is broad at 473 ± 30 keV and "is consistent with a single γ-ray spectral line [of flux] (1.8 ± 0.5) x 10-3 photons cm-2 s-1 keV-1 at the top of the Earth's atmosphere ... Gamma-ray lines in the 0.5-MeV energy region may arise from either the annihilation of positrons or from the de-excitation of nuclei. However, it seems likely, on the basis of evidence presented herein, that the energy of the peak is not at 0.511 MeV (unless the radiation is redshifted by ~0.07 in energy).".
More recent measurements from 1979 through 2003 with germanium detectors observed the peak at 511 keV. "[A] single point source is inconsistent with the data. Formally, we cannot exclude the possibility that the emission originates in at least 2 point sources."
Seyfert 1 coronasEdit
"On the basis of spectroscopic observations, the leading models of the X-ray continuum production are based on a hot, Comptonizing electron or electron-positron pair corona close to the black hole."
"The Earth’s magnetic field significantly affects the CR distribution in near-Earth space. At energies below 10 GeV, a significant fraction of the incoming particles are deflected back to interplanetary space by the magnetic field (“geomagnetic cutoff”). The exact value of the geomagnetic cutoff rigidity depends on the detector position and viewing angle. In addition to the geomagnetic cutoff effect, the Earth blocks trajectories for particles of certain rigidities and directions while allowing other trajectories. This results in a different rate of CRs from the east than the west (the “east-west effect”) [24–26]."
"Positive charges propagating toward the east are curved outward, while negative charges are curved inward toward the Earth [...] This results in a region of particle directions from which positrons can arrive, while electrons are blocked by the Earth. At each particle rigidity there is a region to the west from which positrons are allowed and electrons are forbidden. There is a corresponding region to the east from which electrons are allowed and positrons are forbidden. The precise size and shape of these regions depend on the particle rigidity and instrument location."
"The GAMMA-400 space observatory will provide precise measurements of gamma rays, electrons, and positrons in the energy range 0.1–3000 GeV."
Measurements "of the cosmic-ray positron fraction as a function of energy have been made using the High-Energy Antimatter Telescope (HEAT) balloon-borne instrument."
"The first flight took place from Fort Sumner, New Mexico, [on May 3, 1994, with a total time at float altitude of 29.5 hr and a mean atmospheric overburden of 5.7 g cm-2] ... The second flight [is] from Lynn Lake, Manitoba, [on August 23, 1995, with a total time at float altitude of 26 hr, and a mean atmospheric overburden of 4.8 g cm-2]".
Fermi Gamma-ray Space TelescopeEdit
"The Large Area Telescope (LAT) is a pair-conversion gamma-ray telescope onboard the Fermi Gamma-ray Space Telescope satellite. It has been used to measure the combined [cosmic-ray] CR electron and positron spectrum from 7 GeV to 1 TeV [20, 21]. The LAT does not have a magnet for charge separation. However, as pioneered by  and , the geomagnetic field can also be used to separate the two species without an onboard magnet. Müller and Tang  used the difference in geomagnetic cutoff for positrons and electrons from the east and west to determine the positron fraction between 10 GeV and 20 GeV. As reported below, we used the shadow imposed by the Earth and its offset direction for electrons and positrons due to the geomagnetic field, to separately measure the spectra of CR electrons and positrons from 20 GeV to 200 GeV. In this energy range, the 68% containment radius of the LAT point-spread function is 0.1° or better and the energy resolution is 8% or better."
"The Large Area Telescope (LAT) detects individual gamma rays using technology similar to that used in terrestrial particle accelerators. Photons hit thin metal sheets, converting to electron-positron pairs, via a process known as pair production. These charged particles pass through interleaved layers of silicon microstrip detectors, causing ionization which produce detectable tiny pulses of electric charge. Researchers can combine information from several layers of this tracker to determine the path of the particles. After passing through the tracker, the particles enter the calorimeter, which consists of a stack of caesium iodide scintillator crystals to measure the total energy of the particles. The LAT's field of view is large, about 20% of the sky. The resolution of its images is modest by astronomical standards, a few arc minutes for the highest-energy photons and about 3 degrees at 100 MeV. The LAT is a bigger and better successor to the EGRET instrument on NASA's Compton Gamma Ray Observatory satellite in the 1990s.
The GRANAT satellite has aboard the [French coded aperture] γ-ray telescope SIGMA which on "January 9  detected Nova Muscae at the very edge of its field of view (FOV)."
"SIGMA provides high-resolution (≈ 15') images of the sky in the 35-1300 keV band (see Paul et al. 1991)."
Granat discovered the electron/positron annihilation line (511 keV) from the galactic microquasar 1E1740-294 and the GRS 1124-683 (X-ray Nova Muscae).
"[P]ositron astronomy results ... have been obtained using the INTEGRAL spectrometer SPI". The positrons are not directly observed by the INTEGRAL space telescope, but "the 511 keV positron annihilation emission is".
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