Positron annihilation in the nuclear outflows of the Milky Way

Panther, F. H.; Crocker, Roland M.; Birnboim, Yuval; Seitenzahl, Ivo R.; Ruiter, Ashley J.

doi:10.1093/mnrasl/slx183

Cited by 14 publications

(17 citation statements)

References 34 publications

(60 reference statements)

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“…In [16], the study was restricted to a steady-state nuclear outflow and the limits of the work can thus put weak constraints on positron injections in a single burst. Single-burst injection of positrons was investigated in more detail in [28,29] and was commented on in particular by Alexis et al [19], who find that a burst of either star formation, or activity of the Milky Way's central supermassive black hole (SMBH) producing 10 57 − 10 60 positrons with energies < 1 MeV could contribute to the Galactic bulge annihilation signal.…”

Section: Galactic Center Positron Sourcesmentioning

confidence: 99%

Positron Transport and Annihilation in the Galactic Bulge

Panther

2018

Galaxies

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The annihilation of positrons in the Milky Way galaxy has been observed for ∼ 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 propagation through all ISM phases in order to reveal the currently uncertain origin of these Galactic positrons. On the other hand, if positrons annihilate close to their sources, an alternative source of MeV positrons with a distribution that matches the annihilation morphology must be identified. In this work, I discuss the various models that have been developed to understand the origin of the 511 keV line from the direction of the Galactic bulge, and the propagation of positrons in the ISM.

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Section: Galactic Center Positron Sourcesmentioning

confidence: 99%

Positron Transport and Annihilation in the Galactic Bulge

Panther

2018

Galaxies

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“…Finkbeiner & Weiner 2007;Boehm 2009). Furthermore, large-scale transport into the Galactic bulge by the Milky Way's nuclear outflow has been effectively ruled out (Panther et al 2017) and diffusion of positrons over large distances is strongly constrained (Jean et al 2009;Martin et al 2012;Alexis et al 2014). Now, one of the great challenges in explaining the origin of the Galactic positrons lies in the fact that positron production is ubiquitous in astrophysical environments.…”

Section: Positron Annihilation In the Milky Waymentioning

confidence: 99%

Gamma-ray lines in modern astrophysics

Panther

2019

Preprint

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Gamma-ray astronomy provides a direct window into the most violent, dynamic processes in the Universe. MeV gamma-ray astronomy in particular allows us to directly observe the process of chemical enrichment of the interstellar medium (ISM) through the decay of radioactive isotopes synthesized by stars and compact objects during their lives, in their death throes and after their deaths. Moreover, gamma-ray lines such as the positron annihilation line can give us a unique view into the propagation of cosmic rays in the Galaxy, as well as hints about unusual transient phenomena that may be responsible for producing the positrons. With modern astrophysics moving forward into a new era of multimessenger astrophysics, the important contributions of MeV gamma-ray astronomy must not be overlooked. I briefly outline some of the important contributions gamma-ray spectroscopy with INTEGRAL has made to our understanding of the universe, and the future perspectives for this dynamic field of astrophysics.

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“…This expectation has been enduringly confounded by measurements, the most recent of which point to (𝐵/𝐷) 511 ∼ 1 (Siegert et al 2016b). This anomaly has been interpreted in two ways: Either positrons propagate away from their putative disc sources, becoming subsequently trapped in the Galactic bulge (e.g., Prantzos 2006;Higdon et al 2009), or a central source populates the bulge by positron transport, either diffusive (Jean et al 2009;Martin et al 2012;Alexis et al 2014) or advective (Jean et al 2009;Crocker & Aharonian 2011;Panther et al 2018b;Churazov et al 2011). These interpretations, however, fail to reproduce details in the morphology ★ E-mail: thomas.siegert@uni-wuerzburg.de or violate kinematic constraints.…”

Section: Introductionmentioning

confidence: 99%

Measuring the smearing of the Galactic 511 keV signal: positron propagation or supernova kicks?

Siegert,

Crocker,

Macias

et al. 2021

Preprint

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We use 15 years of 𝛾-ray data from INTEGRAL/SPI in a refined investigation of the morphology of the Galactic bulge positron annihilation signal. Our spatial analysis confirms that the signal traces the old stellar population in the bulge and reveals for the first time that it traces the boxy bulge and nuclear stellar bulge. Using a 3D smoothing kernel, we find that the signal is smeared out over a characteristic length scale of 150 ± 50 pc, suggesting either annihilation in situ at astrophysical sources kicked at formation or positron propagation away from sources. The former is disfavoured by its requiring kick velocities different between the Galactic nucleus ( 50 km s −1 ) and wider bulge ( 15 km s −1 ) source. Positron propagation prior to annihilation can explain the overall phenomenology of the 511 keV signal for positrons injection energies 1.4 MeV, suggesting a nucleosynthesis origin.

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Positron annihilation in the nuclear outflows of the Milky Way

Cited by 14 publications

References 34 publications

Positron Transport and Annihilation in the Galactic Bulge

Positron Transport and Annihilation in the Galactic Bulge

Gamma-ray lines in modern astrophysics

Measuring the smearing of the Galactic 511 keV signal: positron propagation or supernova kicks?

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