Understanding the diffuse gamma ray emission of the milky way - from supernova remnants to dark matter

Diffuse gamma ray emission from the Galactic center at 2-3 GeV, as well as the 12 TeV gamma ray excess in the Galactic disk, remain open for debate and represent the missing puzzles in the complete picture of the high-energy Milky Way sky. Our papers emphasize the importance of understanding all of the populations that contribute to the diffuse gamma background in order to discriminate between the astrophysical sources such as supernova remnants and pulsars, and something that is expected to be seen in gamma rays and is much more exotic - dark matter. We analyze two separate data sets that have been measured in different energy ranges from the ?Fermi-LAT? and ?Milagro? telescopes, using these as a powerful tool to limit and test our analytical source population models. We model supernova remnants and pulsars, estimating the number of still undetected ones that contribute to the diffuse background, trying to explain both the Galactic center and the 12 TeV excess. Furthermore, we aim to predict the number of soon to be detected sources with new telescopes, such as the ?HAWC?.

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The H.E.S.S. Galactic plane survey

Astronomy and Astrophysics ◽

10.1051/0004-6361/201732098 ◽

2018 ◽

Vol 612 ◽

pp. A1 ◽

Cited By ~ 87

Author(s):

◽

H. Abdalla ◽

A. Abramowski ◽

F. Aharonian ◽

F. Ait Benkhali ◽

...

Keyword(s):

Supernova Remnants ◽

Large Scale ◽

Gamma Ray ◽

Galactic Center ◽

Galactic Plane ◽

High Energy ◽

High Angular Resolution ◽

Data Set ◽

Cherenkov Telescopes ◽

Spatial Coverage

We present the results of the most comprehensive survey of the Galactic plane in very high-energy (VHE) γ-rays, including a public release of Galactic sky maps, a catalog of VHE sources, and the discovery of 16 new sources of VHE γ-rays. The High Energy Spectroscopic System (H.E.S.S.) Galactic plane survey (HGPS) was a decade-long observation program carried out by the H.E.S.S. I array of Cherenkov telescopes in Namibia from 2004 to 2013. The observations amount to nearly 2700 h of quality-selected data, covering the Galactic plane at longitudes from ℓ = 250° to 65° and latitudes |b|≤ 3°. In addition to the unprecedented spatial coverage, the HGPS also features a relatively high angular resolution (0.08° ≈ 5 arcmin mean point spread function 68% containment radius), sensitivity (≲1.5% Crab flux for point-like sources), and energy range (0.2–100 TeV). We constructed a catalog of VHE γ-ray sources from the HGPS data set with a systematic procedure for both source detection and characterization of morphology and spectrum. We present this likelihood-based method in detail, including the introduction of a model component to account for unresolved, large-scale emission along the Galactic plane. In total, the resulting HGPS catalog contains 78 VHE sources, of which 14 are not reanalyzed here, for example, due to their complex morphology, namely shell-like sources and the Galactic center region. Where possible, we provide a firm identification of the VHE source or plausible associations with sources in other astronomical catalogs. We also studied the characteristics of the VHE sources with source parameter distributions. 16 new sources were previously unknown or unpublished, and we individually discuss their identifications or possible associations. We firmly identified 31 sources as pulsar wind nebulae (PWNe), supernova remnants (SNRs), composite SNRs, or gamma-ray binaries. Among the 47 sources not yet identified, most of them (36) have possible associations with cataloged objects, notably PWNe and energetic pulsars that could power VHE PWNe.

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High energy diffuse gamma-ray emission of the galactic disk and galactic cosmic-ray spectra

Astroparticle Physics ◽

10.1016/j.astropartphys.2006.03.004 ◽

2006 ◽

Vol 25 (5) ◽

pp. 328-341 ◽

Cited By ~ 2

Author(s):

Thoudam Satyendra

Keyword(s):

Gamma Ray ◽

Galactic Disk ◽

Cosmic Ray ◽

High Energy ◽

Gamma Ray Emission ◽

Galactic Cosmic Ray

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Possible dark matter origin of the gamma ray emission from the Galactic Center observed by HESS

Physical Review D ◽

10.1103/physrevd.86.103506 ◽

2012 ◽

Vol 86 (10) ◽

Cited By ~ 23

Author(s):

J. A. R. Cembranos ◽

V. Gammaldi ◽

A. L. Maroto

Keyword(s):

Dark Matter ◽

Gamma Ray ◽

Galactic Center ◽

Gamma Ray Emission

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H.E.S.S. observations of RX J1713.7−3946 with improved angular and spectral resolution: Evidence for gamma-ray emission extending beyond the X-ray emitting shell

Astronomy and Astrophysics ◽

10.1051/0004-6361/201629790 ◽

2018 ◽

Vol 612 ◽

pp. A6 ◽

Cited By ~ 52

Author(s):

◽

H. Abdalla ◽

A. Abramowski ◽

F. Aharonian ◽

F. Ait Benkhali ◽

...

Keyword(s):

Gamma Rays ◽

Supernova Remnants ◽

Gamma Ray ◽

High Energy ◽

High Energy Gamma ◽

The Past ◽

Very High Energy ◽

Energy Gamma ◽

Gamma Ray Emission ◽

Very High

Supernova remnants exhibit shock fronts (shells) that can accelerate charged particles up to very high energies. In the past decade, measurements of a handful of shell-type supernova remnants in very high-energy gamma rays have provided unique insights into the acceleration process. Among those objects, RX J1713.7−3946 (also known as G347.3−0.5) has the largest surface brightness, allowing us in the past to perform the most comprehensive study of morphology and spatially resolved spectra of any such very high-energy gamma-ray source. Here we present extensive new H.E.S.S. measurements of RX J1713.7−3946, almost doubling the observation time compared to our previous publication. Combined with new improved analysis tools, the previous sensitivity is more than doubled. The H.E.S.S. angular resolution of 0.048° (0.036° above 2 TeV) is unprecedented in gamma-ray astronomy and probes physical scales of 0.8 (0.6) parsec at the remnant’s location. The new H.E.S.S. image of RX J1713.7−3946 allows us to reveal clear morphological differences between X-rays and gamma rays. In particular, for the outer edge of the brightest shell region, we find the first ever indication for particles in the process of leaving the acceleration shock region. By studying the broadband energy spectrum, we furthermore extract properties of the parent particle populations, providing new input to the discussion of the leptonic or hadronic nature of the gamma-ray emission mechanism.

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Status of dark matter in the universe

International Journal of Modern Physics D ◽

10.1142/s0218271817300129 ◽

2017 ◽

Vol 26 (06) ◽

pp. 1730012 ◽

Cited By ~ 28

Author(s):

Katherine Freese

Keyword(s):

Dark Matter ◽

Galaxy Formation ◽

Gravitational Lensing ◽

Gamma Ray ◽

Galactic Center ◽

Data Sets ◽

Multiple Sources ◽

Microwave Background ◽

First Stars ◽

The Universe

Over the past few decades, a consensus picture has emerged in which roughly a quarter of the universe consists of dark matter. I begin with a review of the observational evidence for the existence of dark matter: rotation curves of galaxies, gravitational lensing measurements, hot gas in clusters, galaxy formation, primordial nucleosynthesis and Cosmic Microwave Background (CMB) observations. Then, I discuss a number of anomalous signals in a variety of data sets that may point to discovery, though all of them are controversial. The annual modulation in the DAMA detector and/or the gamma-ray excess seen in the Fermi Gamma Ray Space Telescope from the Galactic Center could be due to WIMPs; a 3.5 keV X-ray line from multiple sources could be due to sterile neutrinos; or the 511 keV line in INTEGRAL data could be due to MeV dark matter. All of these would require further confirmation in other experiments or data sets to be proven correct. In addition, a new line of research on dark stars is presented, which suggests that the first stars to exist in the universe were powered by dark matter heating rather than by fusion: the observational possibility of discovering dark matter in this way is discussed.

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On the origin of the very-high energy gamma-ray emission of the Galactic Center region

10.22323/1.236.0882 ◽

2016 ◽

Author(s):

Aion Viana ◽

Felix Aharonian ◽

Stefano Gabici ◽

Karl Kosack ◽

Emmanuel Moulin ◽

...

Keyword(s):

Gamma Ray ◽

Galactic Center ◽

High Energy ◽

High Energy Gamma ◽

Center Region ◽

Very High Energy ◽

Energy Gamma ◽

Gamma Ray Emission ◽

Very High

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Chapter 2 Galactic Gamma-ray Sources

Chinese Physics C ◽

10.1088/1674-1137/ac3fa8 ◽

2021 ◽

Author(s):

Yang Chen ◽

Xiao Zhang

Keyword(s):

Supernova Remnants ◽

Gamma Ray ◽

Galactic Center ◽

Galactic Plane ◽

Theoretical Models ◽

High Energy ◽

Maximum Energy ◽

Radiation Mechanisms ◽

Galactic Sources ◽

Very High

Abstract In the gamma-ray sky, the highest fluxes come from Galactic sources: supernova remnants (SNRs), pulsars and pulsar wind nebulae, star forming regions, binaries and micro-quasars, giant molecular clouds, Galactic center, and the large extended area around the Galactic plane. The radiation mechanisms of -ray emission and the physics of the emitting particles, such as the origin, acceleration, and propagation, are of very high astrophysical significance. A variety of theoretical models have been suggested for the relevant physics and emission with energies E_1014 eV are expected to be crucial in testing them. In particular, this energy band is a direct window to test at which maximum energy a particle can be accelerated in the Galactic sources and whether the most probable source candidates such as Galactic center and SNRs are “PeVatrons”. Designed aiming at the very high energy (VHE, >100 GeV) observation, LHAASO will be a very powerful instrument in these astrophysical studies. Over the past decade, great advances have been made in the VHE -ray astronomy. More than 170 VHE -ray sources have been observed, and among them, 42 Galactic sources fall in the LHAASO field-of-view. With a sensitivity of 10 milli-Crab, LHAASO can not only provide accurate spectrum for the known -ray sources, but also search new TeV -ray sources. In the following sub-sections, the observation of all the Galactic sources with LHAASO will be discussed in details.

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Hard and bright gamma-ray emission at the base of the Fermi bubbles

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834670 ◽

2019 ◽

Vol 625 ◽

pp. A110 ◽

Cited By ~ 4

Author(s):

L. Herold ◽

D. Malyshev

Keyword(s):

Power Law ◽

Supernova Remnants ◽

Gamma Ray ◽

Galactic Center ◽

Galactic Plane ◽

Point Sources ◽

High Latitudes ◽

Large Area ◽

Inverse Compton Scattering ◽

Gamma Ray Emission

Context. The Fermi bubbles (FBs) are large gamma-ray emitting lobes extending up to 55° in latitude above and below the Galactic center (GC). Although the FBs were discovered eight years ago, their origin and the nature of the gamma-ray emission are still unresolved. Understanding the properties of the FBs near the Galactic plane may provide a clue to their origin. Previous analyses of the gamma-ray emission at the base of the FBs, what remains after subtraction of Galactic foregrounds, have shown an increased intensity compared to the FBs at high latitudes, a hard power-law spectrum without evidence of a cutoff up to approximately 1 TeV, and a displacement of the emission to negative longitudes relative to the GC. Aims. We analyze nine years of Fermi Large Area Telescope data in order to study in more detail than the previous analyses the gamma-ray emission at the base of the FBs, especially at energies above 10 GeV. Methods. We used a template analysis method to model the observed gamma-ray data and calculate the residual emission after subtraction of the expected foreground and background emission components. Since there are large uncertainties in the determination of the Galactic gamma-ray emission toward the GC, we used several methods to derive Galactic gamma-ray diffuse emission and the contribution from point sources to estimate the uncertainties in the emission at the base of the FBs. Results. We confirm that the gamma-ray emission at the base of the FBs is well described by a simple power law up to 1 TeV energies. The 95% confidence lower limit on the cutoff energy is about 500 GeV. It has larger intensity than the FBs emission at high latitudes and is shifted to the west (negative longitudes) from the GC. If the emission at the base of the FBs is indeed connected to the high-latitude FBs, then the shift of the emission to negative longitudes disfavors models in which the FBs are created by the supermassive black hole at the GC. We find that the gamma-ray spectrum can be explained either by gamma rays produced in hadronic interactions or by leptonic inverse Compton scattering. In the hadronic scenario, the emission at the base of the FBs can be explained either by several hundred supernova remnants (SNRs) near the GC or by about ten SNRs at a distance of ~1 kpc. In the leptonic scenario, the necessary number of SNRs that can produce the required density of CR electrons is a factor of a few larger than in the hadronic scenario.

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