First constraints on axionlike particles from Galactic sub-PeV gamma rays

The LHAASO collaboration recently reported a robust measurement of the diffuse gamma-ray emission from the Galactic plane at energies from ∼ 10 TeV up to the PeV. This observation represents a clear evidence of a higher diffuse gamma-ray flux from the Galaxy than the expected from traditional models of CR interactions. On top of this, the recent detection of neutrinos from the Galactic plane by the IceCube collaboration show a similar excess with respect to previous estimations, which further support a larger rate of hadronic interactions in the Galaxy that would explain both observations. However, the uncertainties in the contribution from sources are still too high to discard this as the origin of these excesses. Here, we present updated comparisons of a model of inhomogeneous propagation of cosmic rays in the Galaxy that is tuned to reproduce the Fermi-LAT measurements across the Galactic plane in the GeV range. We show further proof that the predictions from this model reproduce the observed gamma-ray diffuse emission from few GeV up to the PeV, which indicate that these emissions are dominated by the emission from cosmic-ray interactions in the Galaxy. Finally, we show how this model perfectly reproduce the measurements from LHAASO in the inner and outer parts of the Galactic plane, as well as the IceCube best-fit measurement.

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“…The estimation of the flux of sub-threshold sources was done in Ref. [23]. As we see, our predictions exceptionally match these observations.…”

Section: Pos(icrc2023)563supporting

confidence: 76%

Galactic diffuse gamma rays meet the PeV frontier

Luque¹,

Grasso²,

Gaggero³

et al. 2023

Proceedings of 38th International Cosmic Ray Conference — PoS(ICRC2023)

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“…We consider the absorption effect induced by CMB and ISRF photons on ultrahigh-energy photons within the Milky Way. Although several studies [30,31,39,40] derived constraints on the ALP parameters from high energy gamma-ray observations of Galactic sources, we emphasize that the photons from the four Galactic sources considered in this study are more energetic. Furthermore, we employ the CL s method [63,64] to establish robust constraints on the ALP parameters, as in [37,38].…”

Section: Asγmentioning

confidence: 93%

Constraints on axion-like particles from the observation of Galactic sources by the LHAASO*

Li 李,

Bi 毕,

Gao 高

et al. 2024

Chinese Phys. C

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High-energy photons may oscillate with axion-like particles (ALPs) when they propagate through the Milky Way's magnetic field, resulting in an alteration in the observed photon energy spectrum. The ultra-high energy gamma-ray spectra, measured by the Large High Altitude Air Shower Observatory (LHAASO) up to $\mathcal{O}(1)~\mathrm{PeV}$, provide a promising opportunity to investigate the ALP-photon oscillation effect. In this study, we utilize the gamma-ray spectra of four Galactic sources measured by LHAASO, including the Crab Nebula, LHAASO J2226+6057, LHAASO J1908+0621, and LHAASO J1825-1326, to explore this effect. We employ the $\rm CL_s$ method to set constraints on the ALP parameters. Combing the observations of the four sources, our analysis reveals that the ALP-photon coupling $g_{a\gamma}$ is constrained to be smaller than $1.4\times10^{-10}$ ${\rm GeV}^{-1}$ for the ALP mass of $\sim 4\times10^{-7} ~\mathrm{eV}$ at the 95\% C.L. By combing the observations of the Crab Nebula from LHAASO and other experiments, we find that the ALP-photon coupling could be set to be about $7.5\times10^{-11}$ ${\rm GeV}^{-1}$ for the ALP mass $\sim 4 \times10^{-7}~\mathrm{eV}$ , which is in close proximity to the CAST constraint.

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“…The strongest limits (g aγ 10 −11 -10 −13 GeV −1 ) at low masses (m a 10 −6 eV) are set by observations of astrophysical photon sources using the signatures that photon-ALP oscillations will imprint on photon spectra: First, photon-ALP oscillations will induce "irregularities". The non-detection of such spectral irregularities has been used to constrain the parameter space using, e.g., gamma-ray observations by HESS [24] and Fermi-LAT [25], observations of the Galactic diffuse gamma-rays by Tibet ASγ and HAWC [26], and using X-ray observations from Chandra [27][28][29]. The Cherenkov Telescope Array (CTA) is expected to improve the limits from HESS and Fermi-LAT [30].…”

Section: Jcap01(2024)044mentioning

confidence: 99%

“…Nevertheless, this choice is appropriate for our purposes: We advocate for a model independent approach to an ALP searches, since current limits based on astrophysical photon-ALP oscillations depend strongly on the modeling of the magnetic fields. Moreover, it suffice to show that the approach is more sensitive than the standard χ 2 search for residuals, which have already been used to set competitive and leading limits [24][25][26][27][28][29].…”

Section: Jcap01(2024)044mentioning

confidence: 99%

Detecting ALP wiggles at TeV energies

Kachelrieß,

Tjemsland

2024

J. Cosmol. Astropart. Phys.

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Axions and axion-like-particles (ALPs) are characterised by their two-photon coupling, which entails so-called photon-ALP oscillations as photons propagate through a magnetic field. These oscillations lead to distinctive signatures in the energy spectrum of high-energy photons from astrophysical sources, allowing one to probe the existence of ALPs. In particular, photon-ALP oscillations will induce energy dependent oscillatory features, or “ALP wiggles”, in the photon spectra. We propose to use the discrete power spectrum to search for ALP wiggles and present a model-independent statistical test. By using PKS 2155-304 as an example, we show that the method has the potential to significantly improve the experimental sensitivities for ALP wiggles, and that the ALP wiggles may be detected using the Cherenkov Telescope Array (CTA) for optimistic values of the photon-ALP coupling constant and the magnetic field. Moreover, we discuss how these sensitivities depend on the modelling of the magnetic field. We find that the use of realistic magnetic field models, due to their larger cosmic variance, substantially enhances detection prospects compared to the use of simplified models.

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First constraints on axionlike particles from Galactic sub-PeV gamma rays

Cited by 12 publications

References 116 publications

Galactic diffuse gamma rays meet the PeV frontier

Galactic diffuse gamma rays meet the PeV frontier

Constraints on axion-like particles from the observation of Galactic sources by the LHAASO*

Detecting ALP wiggles at TeV energies

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