The Physics of Positron Annihilation in the Solar Atmosphere

Murphy, R. J.; Share, G. H.; Skibo, J. G.; Kozlovsky, B.

doi:10.1086/452634

Cited by 81 publications

(97 citation statements)

References 58 publications

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“…Indeed, the depth at which positrons annihilate depends on the thermodynamic conditions of the gas (density, temperature), and using the energy loss rate of positrons in a totally ionized medium (see Eq. (3) of Murphy et al 2005, and additional references therein), we estimate that the depth at which positrons with initial kinetic energy of 660 keV annihilate is ∼0.1 g cm −2 for a temperature of 10 4 K and ∼0.06 g cm…”

Section: Annihilation In the Atmosphere Of The Companion Starmentioning

confidence: 84%

Microquasars as sources of positron annihilation radiation

Guessoum¹,

Jean²,

Prantzos³

2006

A&A

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We consider the production of positrons in microquasars, i.e. X-ray binary systems that exhibit jets frequently, but not continuously. We estimate the production rate of positrons in microquasars, both by simple energy considerations and in the framework of various proposed models. We then evaluate the collective emissivity of the annihilation radiation produced by Galactic microquasars and we find that it might constitute a substantial contribution to the annihilation flux measured by INTEGRAL/SPI. We also discuss the possible spatial distribution of Galactic microquasars, on the basis of the (scarce) available data and the resulting morphology of the flux received on Earth. Finally, we consider nearby "misaligned" microquasars, with jets occasionally hitting the atmosphere of the companion star; these would represent interesting point sources, for which we determine the annihilation flux and the corresponding light curve, as well as the line's spectral profile. We discuss the possibility of detection of such point sources by future instruments.

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Section: Annihilation In the Atmosphere Of The Companion Starmentioning

confidence: 84%

Microquasars as sources of positron annihilation radiation

Guessoum¹,

Jean²,

Prantzos³

2006

A&A

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“…Although the cross section for annihilation is energy-dependent (e.g. Murphy et al 2005), the assumption that the cross section is the Thompson cross section and the particle speed the speed of light overestimates the cross section for all but the very lowest energies; thus, taking the timescale τ ann = n/(dn/dt) = (nσ T c) −1 gives a conservative lower limit. If we take the rest-frame energy density for the jet given above, then the number density of relativistic electrons (with n(γ) ∝ γ −2 , assuming γ min = 1 and γ max = 10 8 ) required is around n e,rel = 3 × 10 −6 cm −3 .…”

Section: Constraints On Energy Density and Magnetic Fieldsmentioning

confidence: 99%

Mass entrainment and turbulence-driven acceleration of ultra-high energy cosmic rays in Centaurus A

Wykes

Croston

Hardcastle

et al. 2013

A&A

127

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Observations of the FR I radio galaxy Centaurus A in radio, X-ray, and gamma-ray bands provide evidence for lepton acceleration up to several TeV and clues about hadron acceleration to tens of EeV. Synthesising the available observational constraints on the physical conditions and particle content in the jets, inner lobes and giant lobes of Centaurus A, we aim to evaluate its feasibility as an ultra-high-energy cosmic-ray source. We apply several methods of determining jet power and affirm the consistency of various power estimates of ∼1 × 10 43 erg s −1 . Employing scaling relations based on previous results for 3C 31, we estimate particle number densities in the jets, encompassing available radio through X-ray observations. Our model is compatible with the jets ingesting ∼3 × 10 21 g s −1 of matter via external entrainment from hot gas and ∼7 × 10 22 g s −1 via internal entrainment from jet-contained stars. This leads to an imbalance between the internal lobe pressure available from radiating particles and magnetic field, and our derived external pressure. Based on knowledge of the external environments of other FR I sources, we estimate the thermal pressure in the giant lobes as 1.5 × 10 −12 dyn cm −2 , from which we deduce a lower limit to the temperature of ∼1.6 × 10 8 K. Using dynamical and buoyancy arguments, we infer ∼440−645 Myr and ∼560 Myr as the sound-crossing and buoyancy ages of the giant lobes respectively, inconsistent with their spectral ages. We re-investigate the feasibility of particle acceleration via stochastic processes in the lobes, placing new constraints on the energetics and on turbulent input to the lobes. The same "very hot" temperatures that allow self-consistency between the entrainment calculations and the missing pressure also allow stochastic UHECR acceleration models to work.

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“…If the positronium atom is ionized (in the jet or as it reaches the intergalactic medium), the positron can annihilate with free electrons or via positroniumformation in a positron-hydrogen collision. The deceleration and annihilation processes have been thoroughly studied in relation to solar flares, and the relevant cross-sections have been calculated [20]. If electrons and positrons-as a pair plasma-exist near the accretion disks of AGN, they can be accelerated by rotating, helical, magnetic fields and ejected from the force-free zone.…”

Section: Discussionmentioning

confidence: 99%

Long-Lived Positronium and AGN Jets

Giblin

Shertzer

2012

ISRN Astronomy and Astrophysics

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We suggest that stable states of positronium might exist in the jets of active galactic nuclei (AGN). Electrons and positrons are created near the accretion disks of supermassive black holes at the centers of AGN and are accelerated along magnetic field lines while within the Alfvèn radius. The conditions in this region are ideal for the creation of bound states of positronium which are stable against annihilation. Traveling at relativistic speeds along the jet, the helical magnetic field enables the atoms to survive for great distances.

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The Physics of Positron Annihilation in the Solar Atmosphere

Cited by 81 publications

References 58 publications

Microquasars as sources of positron annihilation radiation

Microquasars as sources of positron annihilation radiation

Mass entrainment and turbulence-driven acceleration of ultra-high energy cosmic rays in Centaurus A

Long-Lived Positronium and AGN Jets

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