LHAASO telescope sensitivity to diffuse gamma-ray signals from the Galaxy

Andrii Neronov and Dmitri Semikoz

Phys. Rev. D 102, 043025 – Published 31 August 2020

Abstract

We estimate the sensitivity of LHAASO telescope for the large angular scale diffuse $γ$ -ray flux in multi-TeV—multi-PeV energy range. We discuss possible sources of the signal in this energy range including the guaranteed flux from cosmic ray interactions in the interstellar medium and possible flux from decaying dark matter. We show that LHAASO will be able to detect the diffuse cosmic ray induced $γ$ -ray flux up to high Galactic latitude regions thus providing firm identification of the Galactic cosmic ray component of the astrophysical neutrino signal detected by IceCube and clarification of the nature of the knee feature of the cosmic ray spectrum. Comparing the diffuse flux sensitivity with the diffuse $γ$ -ray flux expected from the dark matter decays, we show LHAASO will be able to detect the $γ$ -ray signal from dark matter particles of PeV–EeV mass decaying on the time scale up to $3 \times 10^{29} s$ .

Received 28 February 2020
Accepted 17 August 2020

DOI:https://doi.org/10.1103/PhysRevD.102.043025

Physics Subject Headings (PhySH)

Cosmic ray sources Dark matter Gamma ray astronomy

Gravitation, Cosmology & Astrophysics

Authors & Affiliations

Andrii Neronov^1,2 and Dmitri Semikoz¹

¹Universit de Paris, CNRS, Astroparticule et Cosmologie, F-75013 Paris, France
²Astronomy Department, University of Geneva, Ch. d’Ecogia 16, 1290 Versoix, Switzerland

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Vol. 102, Iss. 4 — 15 August 2020

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Images

Figure 1
Residual charged cosmic ray backgrounds for the diffuse $γ$ -ray detection in Fermi/LAT [2], HESS (electron spectrum analysis) [9], HAWC [32], and LHAASO [33]. Grey dashed lines with markers show the fractional levels of the overall cosmic ray flux (from $10^{- 6}$ to $10^{- 3}$ ).
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Figure 2
Comparison of one-year exposures of HAWC [32] and LHAASO [33] of a sky revion within the telescope field-of-view with the HAWC exposure of the Fermi Bubble region considered for the dark matter decay signal search by Abeysekara et al. [34, 35].
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Figure 3
Comparison of the sensitivity LHAASO and HAWC with model predictions of gamma-ray flux from cosmic ray interaction in the interstellar medium. Thin grey thin shaded levels in 0.3–3 TeV energy range show the measurements of diffuse Galactic $γ$ -ray flux with Fermi/LAT, in the sky regions $| l | < 30 °$ , $| b | < 2 °$ ; $150 ° < l < 210 °$ , $| b | < 2 °$ ; $10 ° < | b | < 30 °$ ; $| b | > 50 °$ (from top to bottom), reported by Neronov and Semikoz [2]. Black thick line shows the all sky averaged flux level [20]. Grey thick line shows a model of pion decay emission produced by proton power law spectrum with cutoff at $E_{p, cut} = 1 PeV$ . Grey thick dotted line shows the spectrum without a high-energy cutoff but modified by the effect of $γ γ$ pair production on cosmic microwave background photons. Yellow and green butterflies show the measurements of the astrophysical neutrino spectrum by IceCube [15, 38]. HAWC limits on the flux from Fermi Bubble region are from Ref. [35]. Limits on diffuse flux are from [39].
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Figure 4
Comparison of the sensitivity LHAASO and HAWC with predictions of the local source (thick grey solid line) and large-scale cosmic ray halo (thick dotted grey line) models. Thin grey shaded levels in 0.3–3 TeV energy range show the measurements of diffuse Galactic $γ$ -ray flux with Fermi/LAT, in the sky regions $| l | < 30 °$ , $| b | < 2 °$ ; $150 ° < l < 210 °$ , $| b | < 2 °$ ; $10 ° < | b | < 30 °$ ; $| b | > 50 °$ (from top to bottom), reported by Neronov and Semikoz [2]. Thick black line is the sky average diffuse flux measurement [20]. Yellow and green butterflies show the measurements of the astrophysical neutrino spectrum by IceCube [38].
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Figure 5
Comparison of the sensitivity LHAASO and HAWC with the expected sky-averaged multimessenger signal from decaying DM with $τ_{DM} = 3 \times 10^{27} s$ , and DM particle mass $m_{DM} = 5 PeV$ , which could explain the IceCube astrophysical neutrino flux [20]. Thin grey shaded levels in 0.3–3 TeV energy range show the measurements of diffuse Galactic $γ$ -ray flux with Fermi/LAT, in the sky regions $| l | < 30 °$ , $| b | < 2 °$ ; $150 ° < l < 210 °$ , $| b | < 2 °$ ; $10 ° < | b | < 30 °$ ; $| b | > 50 °$ (from top to bottom), reported by Neronov and Semikoz [2].
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Figure 6
Sensitivity of LHAASO for the measurement of dark matter decay time (for DM decaying into quarks). Yellow band shows the range of decay times for which DM decays give sizeable contribution to the IceCube neutrino signal [20]. Blue and grey shaded regions show the existing bounds imposed by HAWC [34] and ultrahigh-energy cosmic ray experiments [59]. and dashed curves are from the HAWC search of the DM decay signal in the Fermi bubble regions [34]. Dashed red line shows an estimate of LHAASO sensitivity for decaying DM from the analysis of a sample of dwarf spheroidal galaxies from Ref. [60].
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