Multi-messenger Implications of Sub-PeV Diffuse Galactic Gamma-Ray Emission

Abstract

The diffuse Galactic gamma-ray flux between 0.1 and 1 PeV has recently been measured by the Tibet ASγ Collaboration. The flux and spectrum are consistent with the decay of neutral pions from hadronuclear interactions between Galactic cosmic rays and the interstellar medium (ISM). We derive the flux of the Galactic diffuse neutrino emission from the same interaction process that produces the gamma rays. Our calculation accounts for the effect of gamma-ray attenuation inside the Milky Way and uncertainties due to the spectrum and distribution of cosmic rays, gas density, and infrared emission of the ISM. We find that the contribution from the Galactic plane to the all-sky neutrino flux is 5 − 10% around 100 TeV. The Galactic and extragalactic neutrino intensities are comparable in the Galactic plane region. Our results are consistent with the upper limit reported by the IceCube and ANTARES Collaborations, and predict that next-generation neutrino experiments may observe the Galactic component. We also show that the Tibet ASγ data imply either an additional component in the cosmic-ray nucleon spectrum or contribution from discrete sources, including Pevatrons such as superbubbles and hypernova remnants, and PeV electron accelerators. Future multi-messenger observations between 1 TeV and 1 PeV are crucial to decomposing the origin of sub-PeV gamma rays.

Chapter 6 Multimessenger Physics *

“…There has been analysis on the diffuse neutrino flux from the Galactic plane, and the upper limit is found to be % [24,94]. The diffuse gamma-ray emission from the Galactic plane at multi-TeV energy would be a direct indicator of Galactic high-energy neutrino flux, although the emission by unresolved faint gamma-ray sources may also contribute [95,96]. Figure 3 shows the expected Galactic diffuse neut-…”

Ultrahigh-energy diffuse gamma-ray emission from cosmic-ray interactions with medium surrounding acceleration sources

“…Some fresh sources in such a region may explain the excess (Bi et al 2009;Guo et al 2016a). Very recently, the DGE in the Galactic plane above 100 TeV energies was for the first time measured by the Tibet-ASγ experiment (Amenomori et al 2021), which has attracted wide attention for possible physical discussion (Kimura et al 2021;Dzhatdoev 2021;Fang & Murase 2021;Liu & Wang 2021;Qiao et al 2021;Huentemeyer 2021;Esmaili & Serpico 2021;Koldobskiy et al 2021;Bouyahiaoui et al 2021;Dzhappuev et al 2021;Li & Ma 2021;Tibaldo et al 2021;Nath Maity et al 2021). The Tibet-ASγ fluxes are higher than the prediction of the conventional CR propagation model, and additional components or modification of the conventional propagation framework may be needed (Amenomori et al 2021;Liu & Wang 2021;Qiao et al 2021).…”

First implications of Tibet AS$_γ$ data for heavy dark matter

“…We forecasted that the forthcoming generation of observatories would attain the needed sensitivity for crucial studies. With the first detection of Galactic gamma-rays up to PeV energies by Tibet AS γ [21] and the commissioning of the LHAASO observatory [22], we are witnessing the dawn of this new astrophysical window, and should prepare to harness its full potential, in particular in a multiwavelength and multimessenger context (see [23][24][25] for initial examples of this approach). In this article, we provide an assessment of the importance of this first detection for DM searches, a task whose relevance has already been recognized in [26].…”