Search for Spectral Irregularities due to Photon-Axionlike-Particle Oscillations With the Fermi Large Area Telescope

Abstract: We report on the search for spectral irregularities induced by oscillations between photons and axionlike-particles (ALPs) in the $\gamma$-ray spectrum of NGC 1275, the central galaxy of the Perseus cluster. Using six years of Fermi Large Area Telescope data, we find no evidence for ALPs and exclude couplings above $5\times10^{-12}\,\mathrm{GeV}^{-1}$ for ALP masses $0.5 \lesssim m_a \lesssim 5$ neV at 95% confidence. The limits are competitive with the sensitivity of planned laboratory experiments, and, together with other bounds, strongly constrain the possibility that ALPs can reduce the $\gamma$-ray opacity of the Universe.

• The paper reports constraints on ALP-photon couplings, excluding values above 5×10⁻¹² GeV⁻¹ for ALP masses between 0.5 and 5 neV from six years of Fermi LAT data.
• A binned Poisson likelihood analysis quantifies energy-dependent spectral deviations while rigorously accounting for systematic uncertainties in the instrument and magnetic field modeling.
• Results refine models of gamma-ray transparency and dark matter, guiding future high-energy surveys such as those by the CTA to explore higher mass and coupling regimes.

Analysis of Photon--Axionlike-Particle Oscillations with the Fermi LAT

This paper presents an investigation into the detection of spectral irregularities due to photon--axionlike-particle (ALP) oscillations within the gamma-ray spectrum of NGC 1275, utilizing data collected by the Fermi Large Area Telescope (LAT). It explores the potential interactions between high-energy photons and ALPs as a function of oscillation parameters, with a focus on implications for dark matter and cosmic ray attenuation studies.

Key Findings

The analysis of six years of Fermi LAT data does not reveal substantial evidence for ALP-induced spectral deviations. The limits set exclude ALP-photon couplings higher than $5 \times 10^{-12} \text{GeV}^{-1}$ for ALP masses between approximately 0.5 neV and 5 neV at a 95% confidence level. These findings are particularly relevant because they provide constraints competitive with upcoming laboratory-based searches, potentially narrowing the parameter space where ALPs could influence the opacity of the Universe to gamma rays.

Methodology

The work employs a binned Poisson likelihood analysis method, which derives likelihood functions in energy bins based on photon statistics expected in the absence and presence of ALPs. The analysis accounts for the intricacies of how ALP coupling parameters and magnetic fields scatter gamma-ray paths, potentially leading to energy-dependent modifications in observed spectra.

The consideration of systematic uncertainties was crucial. These include the modeling of intra-cluster magnetic fields, effects of the telescope's energy reconstruction accuracy, and possible unknown systematic biases in the instrument's effective area. Testing alternative assumptions about the intra-cluster magnetic field, such as different core strengths, turbulence spectra, or radial dependence, provides a robust understanding of potential variabilities in the results.

Implications

The analysis has profound implications for the understanding of ALPs as possible components of dark matter. The constraints obtained from this search significantly limit ALP models that could otherwise reduce the attenuation of gamma rays more than currently observable by extragalactic background light (EBL) models. Moreover, by excluding significant parameter spaces within which ALPs could affect cosmic transparency, this research refines the landscape for ALP's role in cosmic ray physics.

Another crucial aspect discussed is the exploration range of future high-energy astrophysical instruments. The Fermi LAT data, although setting tight constraints, leaves room for upcoming missions like the Cherenkov Telescope Array (CTA) or Gamma-400 to further test higher mass regions and tighter couplings due to their advanced resolution capabilities.

Future Prospects

As the methodology adapts to new instruments and as our understanding of cosmic magnetic fields improves, further refinement of these constraints is expected. Future analyses might expand to include other emitters within galaxy clusters, potentially revealing complementary interactions between gamma rays and ALPs.

In conclusion, while the present study does not find evidence of ALP presence through photon oscillations in NGC 1275, it emphasizes the need for continued high-sensitivity surveys in pursuit of astrophysical phenomena that challenge current particle physics theories. The rigorous attention to systematic effects sets a benchmark for future explorations into the interaction of fundamental particles in cosmic settings.