Blazar Constraints on Axions through New Spectral Modulation Searches in 1ES 1959+650 & B2 1811+31

Abstract

Blazars are unique astrophysical environments whose high-energy $γ$-ray spectra are susceptible to modulations in the presence of ultralight axions. We search for these modulations, induced by axion-photon mixing, in Fermi-LAT spectral data of previously unexplored blazar targets, focusing in particular on blazars 1ES 1959+650 and B2 1811+31, whose flare states provide a clean testbed for axion activity. In both cases, we find no evidence for axions, and set exclusion regions on the axion-photon coupling for masses between $10^{-9}$ eV $\lesssim$ $m_a$ $\lesssim$ $10^{-8}$ eV, with sensitivities typically reaching $g_{a γγ} \sim 10^{-11} - 10^{-10}$ GeV$^{-1}$ depending on the assumed blazar modeling choices. We examine the broad impact of modeling uncertainties, finding that the resulting constraints can vary substantially across plausible configurations. We discuss the implications of these systematic effects and their relevance for similar blazar-like searches in the future.

Figures (11)

• Figure 1: The configuration-dependent 95% exclusion regions on $g_{a \gamma \gamma}$ obtained in this work from the non-observation of axion-induced spectral modulations in the $\gamma$-ray spectra of our blazar targets, 1ES 1959+650 and B2 1811+31. We illustrate representative constraints from several fiducial astrophysical configurations: Configurations 1 and 4 for 1ES 1959+650, corresponding to two plausible choices of magnetic field strength and emission region size, and the one-zone and two-zone emission models for B2 1811+31 (note that the one-zone model is disfavored through complementary observations, see main text). The inset highlights the regions simultaneously excluded by multiple configurations for each blazar (among all configurations considered for each), indicating parameter space where constraints would likely be more robust against modeling uncertainties. We compare to existing constraints in gray AxionLimits.
• Figure 2: (Left) The survival probability at the given axion parameters $m_a$ and $g_{a \gamma \gamma}$ as a function of energy, for our four configurations of blazar target 1ES 1959+650 (see Table \ref{['tab:blazar_targets']}). (Right) The same but for our one/two-zone models of blazar target B2 1811+31.
• Figure 3: (Left) The Fermi-LAT spectral data for our blazar target 1ES 1959+650 compared to example axion-induced modulations over our four main fiducial configurations (see Table \ref{['tab:blazar_targets']}) for the indicated mass and coupling. Also shown is the fit under the null hypothesis (gray). (Right) The same but for blazar target B2 1811+31 and its two fiducial models.
• Figure 4: The distribution of $q_{\rm MC}$ over our MC ensemble ($N = 500$) of systematic configurations of blazar target 1ES 1959+650 (see main text). We illustrate the derived $q_{95}$ value in dashed red, with its value indicated. The ordering top left, top right, bottom left, bottom right corresponds to configurations 1, 2, 3, 4, respectively.
• Figure 5: The same as Fig. \ref{['fig:MC_1ES']} but for blazar target B2 1811+31. In the left panel we show the distribution of $q_{\rm MC}$ and the resulting $q_{95}$ value for the one-zone model without the core emission region, while in the right panel we include the core region in the two-zone model.