Galactic binaries can explain the Fermi Galactic centre excess and 511 keV emission

Bartels, Richard; Calore, Francesca; Storm, Emma; Weniger, Christoph

doi:10.1093/mnras/sty2135

Cited by 32 publications

(28 citation statements)

References 152 publications

(260 reference statements)

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“…This is the most conservative option; if we had assumed the contribution of some astrophysical source(s) to this gamma-ray observation, then the upper limit on the positron injection luminosity would have been much lower. The flux of this line in the bulge and the central source of our Galaxy is (0.96 ± 0.07) × 10 −3 photons cm −2 s −1 and (0.08 ± 0.02) × 10 −3 photons cm −2 s −1 respectively [61]. Thus, our limits can be improved by more than an order of magnitude if one identifies the class(es) of astrophysical source(s) which is contributing to this emission in the Galactic bulge.…”

Section: Formalismmentioning

confidence: 82%

“…Despite the intense scrutiny of this signal, we do not yet know the origin of this signal. Many viable astrophysical models (i.e., models which do not require a dark matter origin of the 511 keV signal) have been proposed [19,[57][58][59][60][61][62], although none are confirmed to be the source of these low energy positrons. A detailed morphological study of this signal and its absence in the dwarf galaxies [63] indicate that this it is not produced via dark matter interactions [64].…”

Section: Introductionmentioning

confidence: 99%

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Primordial Black Holes as a Dark Matter Candidate Are Severely Constrained by the Galactic Center 511 keVγ-Ray Line

2019

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We derive the strongest constraint on the fraction of dark matter that can be composed of low mass primordial black holes by using the observation of the Galactic Center 511 keV gamma-ray line. Primordial black holes of masses 10 15 kg will evaporate to produce e ± pairs. The positrons will lose energy in the Galactic Center, become non-relativistic, and then annihilate with the ambient electrons. We derive robust and conservative bounds by assuming that the rate of positron injection via primordial black hole evaporation is less than what is required to explain the SPI/ INTEGRAL observation of the Galactic Center 511 keV gamma-ray line. Depending on the primordial black hole mass function and other astrophysical uncertainties, these constraints are the most stringent in the literature and show that primordial black holes contribute to less than 1% of the dark matter density. Our technique also probes part of the mass range which was completely unconstrained by previous studies.

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Section: Formalismmentioning

confidence: 82%

Section: Introductionmentioning

confidence: 99%

Primordial Black Holes as a Dark Matter Candidate Are Severely Constrained by the Galactic Center 511 keVγ-Ray Line

2019

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“…If positron annihilation is occuring in an environment where relativistic electrons are present (e.g. in a microquasar jet [13,14] or pulsars and millisecond pulsars, [15]) it may be possible to circumvent this constraint. However, the presence of the 511 keV line and ortho-positronium continuum at low gamma-ray energies strongly suggest that the majority of positrons annihilate via interactions with neutral hydrogen at thermal energies.…”

Section: Introductionmentioning

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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“…The nuclear stellar cluster as well as a large number of the Milky Way's globular clusters would stand out of the otherwise diffuse glow and provide direct evidence for these types of scenarios. With arcmin resolution, it would furthermore be possible to distinguish among mildly relativistic, quiescent XRB outflows [7] or stellar flares as the latter would directly follow the globular cluster's radial profile.…”

Section: Candidate Sources -Detecting Sources In Flagrantimentioning

confidence: 99%

Understanding the origin of the positron annihilation line and the physics of supernova explosions

et al. 2021

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Nuclear astrophysics, and particularly nuclear emission line diagnostics from a variety of cosmic sites, has remained one of the least developed fields in experimental astronomy, despite its central role in addressing a number of outstanding questions in modern astrophysics. Radioactive isotopes are co-produced with stable isotopes in the fusion reactions of nucleosynthesis in supernova explosions and other violent events, such as neutron star mergers. The origin of the 511 keV positron annihilation line observed in the direction of the Galactic Center is a 50-year-long mystery. In fact, we still do not understand whether its diffuse large-scale emission is entirely due to a population of discrete sources, which are unresolved with current poor angular resolution instruments at these energies, or whether dark matter annihilation could contribute to it. From the results obtained in the pioneering decades of this experimentally-challenging window, it has become clear that some of the most pressing issues in high-energy astrophysics and astro-particle physics would greatly benefit from significant progress in the observational capabilities in the keV-to-MeV energy band. Current instrumentation is in fact not sensitive enough to detect radioactive and annihilation lines from a wide variety of phenomena in our and nearby galaxies, let alone study the spatial distribution of their emission. In this White Paper (WP), we discuss how unprecedented studies in this field will become possible with a new low-energy gamma-ray space experiment, called ASTENA (Advanced Surveyor of Transient Events and Nuclear Astrophysics), which combines new imaging, spectroscopic and polarization capabilities. In a separate WP (Guidorzi et al. 39), we discuss how the same mission concept will enable new groundbreaking studies of the physics of Gamma–Ray Bursts and other high-energy transient phenomena over the next decades.

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Galactic binaries can explain the Fermi Galactic centre excess and 511 keV emission

Cited by 32 publications

References 152 publications

Primordial Black Holes as a Dark Matter Candidate Are Severely Constrained by the Galactic Center 511 keVγ-Ray Line

Primordial Black Holes as a Dark Matter Candidate Are Severely Constrained by the Galactic Center 511 keVγ-Ray Line

Positron Transport and Annihilation in the Galactic Bulge

Understanding the origin of the positron annihilation line and the physics of supernova explosions

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