The Interstellar Radiation Field of the Milky Way in Three Spatial Dimensions

Abstract. Over the past decade, extensive studies have been undertaken to search for photon signals from dark matter annihilation or decay for dark matter particle masses above ∼ 1 GeV. However, due to the lacking sensitivity of current experiments at MeV-GeV energies, sometimes dubbed the 'MeV gap', dark matter models with MeV to sub-GeV particle masses have received little attention so far. Various proposed MeV missions (like, e.g., e-ASTROGAM or AMEGO) are aimed at closing this gap in the mid-or long-term future. This, and the absence of clear dark matter signals in the GeV-TeV range, makes it relevant to carefully reconsider the expected experimental instrumental sensitivities in this mass range. The most common two-body annihilation channels for sub-GeV dark matter are to neutrinos, electrons, pions or directly to photons. Among these, only the electron channel has been extensively studied, and almost exclusively in the context of the 511 keV line. In this work, we study the prospects for detecting MeV dark matter annihilation in general in future MeV missions, using e-ASTROGAM as reference, and focusing on dark matter masses in the range 1 MeV-3 GeV. In the case of leptonic annihilation, we emphasise the importance of the often overlooked bremsstrahlung and in-flight annihilation spectral features, which in many cases provide the dominant gamma-ray signal in this regime.

show abstract

“…• The interstellar radiation field is taken from the public version of GALPROP; it is described in [75,76].…”

Section: Brems Coulomb Ics Ionization Synchrotron In-flight Annihilat...mentioning

confidence: 99%

Prospects for indirect dark matter searches with MeV photons

Bartels

Gaggero

Weniger

2017

J. Cosmol. Astropart. Phys.

117

View full text Add to dashboard Cite

show abstract

“…The smooth disc spatial density follows the radial distribution of pulsars as given by [19]. The spiral arm spatial density follows that of the 4 major arms in the R12 model [14] and assumes an identical injection of CR power by each arm. The CR source density models are termed SA0, SA50, and SA100, following the proportion of injected CR luminosity by the spiral arms.…”

Section: Calculations and Resultsmentioning

confidence: 96%

“…Three CR source density models are considered that have the injected CR power distributed as a mixture of an axisymmetric smooth disc and/or spiral arms. Two 3D ISRF models termed R12 and F98 that are described elsewhere [14] are developed and their Galaxy-wide spectral intensity distributions are calculated. The new release of the GALPROP code [15] is employed using these CR and ISRF density models as inputs for the CR propagation and high-energy interstellar emission calculations.…”

Section: Pos(icrc2017)736mentioning

confidence: 99%

High-Energy Gamma-Rays from the Milky Way: Three-Dimensional Spatial Models for the Cosmic-Ray and Radiation Field Densities

Porter¹,

Jóhannesson²,

Москаленко³

2017

Proceedings of 35th International Cosmic Ray Conference — PoS(ICRC2017)

Self Cite

View full text Add to dashboard Cite

High-energy γ-rays of interstellar origin are produced by the interaction of cosmic-ray (CR) particles with the diffuse gas and radiation fields in the Galaxy. The main features of this emission are well understood and are reproduced by existing CR propagation models employing 2D Galactocentric cylindrically symmetrical geometry. However, the high-quality data from instruments like the Fermi Large Area Telescope reveal significant deviations from the model predictions on few to tens of degree scales indicating the need to include the details of the Galactic spiral structure and thus require 3D spatial modelling. In this contribution the high-energy interstellar emissions from the Galaxy are calculated using the latest release of the GALPROP code employing 3D spatial models for the CR source and interstellar radiation field (ISRF) densities. The interstellar emission models that include arms and bulges for the CR source and ISRF densities provide plausible physical interpretations for features found in the residual maps from high-energy γ-ray data analysis. The 3D models for CR and ISRF densities provide a more realistic basis that can be used for the interpretation of the non-thermal interstellar emissions from the Galaxy.

show abstract

“…based on the analytic approximation presented in Khangulyan et al (2014), the VHE γ-ray emission was attributed to inverse-Compton up-scattering by electrons of the cosmic microwave background (CMB) and infrared (IR) low-energy photon fields. The uniform CMB field was described as a black-body radiation with energy density of CMB = 0.261 eV cm −3 and temperature of T CMB = 2.73 K. The starlight emission in the near IR ( NIR = 1 eV cm −3 and T NIR = 3000 K) and dust re-emission in the far IR ( FIR = 0.5 eV cm −3 and T FIR = 30 K) were obtained using the 3D interstellar radiation field (ISRF) model from Porter et al (2018), at the coordinates of HESS J1702-420 and the assumed 3.5 kpc distance. We verified that the level of fluctuations of the ISRF along the line of sight did not significantly impact the modeling conclusions.…”

Section: Discussionmentioning

confidence: 99%

Evidence of 100 TeV γ-ray emission from HESS J1702-420: A new PeVatron candidate

Abdalla

Aharonian²,

Benkhali³

et al. 2021

A&A

View full text Add to dashboard Cite

Aims. The identification of PeVatrons, hadronic particle accelerators reaching the knee of the cosmic ray spectrum (few × 1015 eV), is crucial to understand the origin of cosmic rays in the Galaxy. We provide an update on the unidentified source HESS J1702-420, a promising PeVatron candidate. Methods. We present new observations of HESS J1702-420 made with the High Energy Stereoscopic System (H.E.S.S.), and processed using improved analysis techniques. The analysis configuration was optimized to enhance the collection area at the highest energies. We applied a three-dimensional likelihood analysis to model the source region and adjust non thermal radiative spectral models to the γ-ray data. We also analyzed archival Fermi Large Area Telescope data to constrain the source spectrum at γ-ray energies > 10 GeV. Results. We report the detection of γ-rays up to 100 TeV from a specific region of HESS J1702-420, which is well described by a new source component called HESS J1702-420A that was separated from the bulk of TeV emission at a 5.4σ confidence level. The power law γ-ray spectrum of HESS J1702-420A extends with an index of Γ = 1.53 ± 0.19stat ± 0.20sys and without curvature up to the energy band 64−113 TeV, in which it was detected by H.E.S.S. at a 4.0σ confidence level. This makes HESS J1702-420A a compelling candidate site for the presence of extremely high energy cosmic rays. With a flux above 2 TeV of (2.08 ± 0.49stat ± 0.62sys) × 10−13 cm−2 s−1 and a radius of (0.06 ± 0.02stat ± 0.03sys)°, HESS J1702-420A is outshone – below a few tens of TeV – by the companion HESS J1702-420B. The latter has a steep spectral index of Γ = 2.62 ± 0.10stat ± 0.20sys and an elongated shape, and it accounts for most of the low-energy HESS J1702-420 flux. Simple hadronic and leptonic emission models can be well adjusted to the spectra of both components. Remarkably, in a hadronic scenario, the cut-off energy of the particle distribution powering HESS J1702-420A is found to be higher than 0.5 PeV at a 95% confidence level. Conclusions. For the first time, H.E.S.S. resolved two components with significantly different morphologies and spectral indices, both detected at > 5σ confidence level, whose combined emissions result in the source HESS J1702-420. We detected HESS J1702-420A at a 4.0σ confidence level in the energy band 64−113 TeV, which brings evidence for the source emission up to 100 TeV. In a hadronic emission scenario, the hard γ-ray spectrum of HESS J1702-420A implies that the source likely harbors PeV protons, thus becoming one of the most solid PeVatron candidates detected so far in H.E.S.S. data. However, a leptonic origin of the observed TeV emission cannot be ruled out either.

show abstract

The Interstellar Radiation Field of the Milky Way in Three Spatial Dimensions

Cited by 5 publications

References 25 publications

Prospects for indirect dark matter searches with MeV photons

Prospects for indirect dark matter searches with MeV photons

High-Energy Gamma-Rays from the Milky Way: Three-Dimensional Spatial Models for the Cosmic-Ray and Radiation Field Densities

Evidence of 100 TeV γ-ray emission from HESS J1702-420: A new PeVatron candidate

Contact Info

Product

Resources

About