Pevatron at the Galactic Center: multi-wavelength signatures from millisecond pulsars (original) (raw)
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Challenges in explaining the Galactic Center gamma-ray excess with millisecond pulsars
Journal of Cosmology and Astroparticle Physics, 2015
Millisecond pulsars have been discussed as a possible source of the gamma-ray excess observed from the region surrounding the Galactic Center. With this in mind, we use the observed population of bright low-mass X-ray binaries to estimate the number of millisecond pulsars in the Inner Galaxy. This calculation suggests that only ∼1-5% of the excess is produced by millisecond pulsars. We also use the luminosity function derived from local measurements of millisecond pulsars, along with the number of point sources resolved by Fermi, to calculate an upper limit for the diffuse emission from such a population. While this limit is compatible with the millisecond pulsar population implied by the number of low-mass X-ray binaries, it strongly excludes the possibility that most of the excess originates from such objects.
Diffusive cosmic-ray acceleration at the Galactic Centre
Monthly Notices of the Royal Astronomical Society: Letters, 2011
The diffuse TeV emission detected from the inner ∼ 2 • of the Galaxy appears to be strongly correlated with the distribution of molecular gas along the Galactic ridge.
Physical Review D
The H.E.S.S. collaboration has reported a high-energy spherically symmetric diffuse γ-ray emission in the inner 50 pc of the Milky Way, up to ∼ 50 TeV. Here we propose a leptonic model which provides an alternative to the hadronic scenario presented by the H.E.S.S. collaboration, and connects the newly reported TeV emission to the Fermi-LAT Galactic center GeV excess. Our model relies on a combination of inverse Compton emission from a population of millisecond pulsars-which can account for the GeV excess-and a supermassive black hole-induced spike of heavy (∼ 60 TeV) dark matter particles annihilating into electrons with a sub-thermal cross-section. With an up-to-date interstellar radiation field, as well as a standard magnetic field and diffusion setup , our model accounts for the spectral morphology of the detected emission. Moreover, we show that the dark matter induced emission reproduces the spatial morphology of the H.E.S.S. signal above ∼ 10 TeV, while we obtain a slightly more extended component from pulsars at lower energies, which could be used as a prediction for future H.E.S.S. observations.
The inner 300 parsecs of the Milky Way seen by H.E.S.S.: a Pevatron in the Galactic Centre
EPJ Web of Conferences, 2017
The Galactic Centre region has been observed by the High Energy Stereoscopic System (H.E.S.S.) array of ground-based Cherenkov telescopes since 2004 leading to the detection of the very-high-energy γ-ray source HESS J1745-290 spatially coincident with the supermassive black hole Sagittarius A*. Diffuse TeV gamma-ray emission has been detected along the Galactic plane, most likely due to hadronic cosmic-ray interactions with the dense gas of the Central Molecular Zone. The rich 2004-2013 dataset permits detailed spectral and morphological studies of the diffuse emission in the inner 300 pc of the Galactic Centre region. The new results provide an important statement regarding the location and origin of the accelerator of PeV protons. The H.E.S.S. observations of the Pevatron are discussed in the context of the origin of Galactic cosmic rays.
PeV gamma rays from interactions of ultra high energy cosmic rays in the Milky Way
Astroparticle Physics, 2012
The PeV gamma ray background produced in the interactions of ultra high energy cosmic rays with the ambient matter and radiations during their propagation in the Milky Way has been calculated in this paper. If the primary ultra high energy cosmic rays are produced from Galactic point sources then those point sources are also emitting PeV gamma rays. We discuss that the detection of galactocentric PeV gamma rays in the future would be a signature of the presence of EeV cosmic accelerators in the Milky Way.
Galactic diffuse gamma rays meet the PeV frontier
Cornell University - arXiv, 2022
Context. The Tibet ASγ and LHAASO collaborations recently reported the observation of a γ-ray diffuse emission with energy up to the PeV from the Galactic plane. Aims. We discuss the relevance of non-uniform cosmic-ray transport scenarios and the implications of these results for cosmic-ray physics. Methods. We use the DRAGON and HERMES codes to build high-resolution maps and spectral distributions of that emission for several representative models under the condition that they reproduce a wide set of local cosmic-ray data up to 100 PeV. Results. We show that the energy spectra measured by Tibet ASγ, LHAASO, ARGO-YBJ and Fermi-LAT in several regions of interest in the sky can all be consistently described in terms of the emission arising by the Galactic cosmic-ray "sea". We also show that all our models are compatible with IceTop γ-ray upper limits. Conclusions. Our results favor transport models characterized by spatial-dependent diffusion although some degeneracy remains between the choice of the transport scenario and that of the cosmic-ray spectral shape above 10 TeV. We discuss the role of forthcoming measurements in resolving that ambiguity.
Galactic diffuse γ-ray emission at TeV energies and the ultra-high energy cosmic rays
AIP Conference Proceedings, 1997
Using the cosmic ray (CR) data available in the energy interval (10 − 2 × 10 7 ) GeV/particle, we have calculated the profile of the primary γ-ray spectrum produced by the interaction of these CR with thermal nuclei of the ISM. Normalized to the EGRET measurements, this allows an estimate of the galactic diffuse γ-ray background due to intermediate and high energy CR at TeV energies. On the other hand, over the last few years, several particles with energies above 10 20 eV (beyond the Greisen-Zatsepin-Kuzmin cut-off) have been detected. These particles are very likely extragalactic protons originated at distances not greater than 30 − 50 Mpc [e.g., 1]. The propagation of these ultra-high energy protons (UHEP) through the intergalactic medium leads to the development of γ-ray cascades and an ultimate signature at TeV energies. To assess the statistical significance of this γ-ray signature by the UHEP, we have also simulated the development of electromagnetic cascades triggered by the decay of a 10 19 eV π o in the intergalactic medium after an UHEP collision with a cosmic microwave background photon.
Galactic diffuse G-ray emission at TeV energies and the ultra-high energy cosmic rays
1997
Using the cosmic ray (CR) data available in the energy interval (10−2times107)(10 - 2 \times 10^{7})(10−2times107) GeV/particle, we have calculated the profile of the primary gamma\gammagamma-ray spectrum produced by the interaction of these CR with thermal nuclei of the ISM. Normalized to the EGRET measurements, this allows an estimate of the galactic diffuse gamma\gammagamma-ray background due to intermediate and high energy CR at TeV energies. On the other hand, over the last few years, several particles with energies above 102010^{20}1020 eV (beyond the Greisen-Zatsepin-Kuzmin cut-off) have been detected. These particles are very likely extragalactic protons originated at distances not greater than 30−5030 - 5030−50 Mpc [e.g., 1]. The propagation of these ultra-high energy protons (UHEP) through the intergalactic medium leads to the development of gamma\gammagamma-ray cascades and an ultimate signature at TeV energies. To assess the statistical significance of this gamma\gammagamma-ray signature by the UHEP, we have also simulated the development of electromagnetic cascades triggered by the decay of a 101910^{19}1019 eV pio\pi^{o}pio in the intergalactic medium after an UHEP collision with a cosmic microwave background photon.
The High-Energy, Arcminute-Scale Galactic Center Gamma-Ray Source
The Astrophysical Journal, 2011
Employing data collected during the first 25 months' observations by the Fermi -LAT, we describe and subsequently seek to model the very high energy (> 300 MeV) emission from the central few parsecs of our Galaxy. We analyse, in particular, the morphological, spectral and temporal characteristics of the central source, 1FGL J1745.6-2900. Remarkably, the data show a clear, statistically significant signal at energies above 10 GeV, where the Fermi -LAT has an excellent angular resolution comparable to the angular resolution of HESS at TeV energies. This not only reduces dramatically the contamination both from the diffuse background and the nearby gamma-ray sources, but also makes meaningful the joint analysis of the Fermi and HESS data. Our analysis does not show statistically significant variability of 1FGL J1745.6-2900. Using the combination of Fermi data on 1FGL J1745.6-2900 and HESS data on the coincident, TeV source HESS J1745-290, we show that the spectrum of the central γ-ray source is inflected with a relatively steep spectral region matching between the flatter spectrum found at both low and high energies. We seek to model the gamma-ray production in the inner 10 pc of the Galaxy and examine, in particular, cosmic ray (CR) proton propagation scenarios that reproduce the observed spectrum of the central source. We show that a model that instantiates a transition from diffusive propagation of the CR protons at low energy to almost rectilinear propagation at high energies (given a reasonable energy-dependence of the assumed diffusion coefficient) can well explain the spectral phenomenology. In general, however, we find considerable degeneracy between different parameter choices which will only be broken with the addition of morphological information that γ-ray telescopes cannot deliver given current angular resolution limits. We argue that a future analysis done in combination with higherresolution radio continuum data holds out the promise of breaking this degeneracy.