First Constraints on the Photon Coupling of Axion-like Particles from Multimessenger Studies of the Neutron Star Merger GW170817

Abstract

We use multimessenger observations of the neutron star merger event GW170817 to derive new constraints on axion-like particles (ALPs) coupling to photons. ALPs are produced via Primakoff and photon coalescence processes in the merger, escape the remnant and decay back into two photons, giving rise to a photon signal approximately along the line-of-sight to the merger. We analyze the spectral and temporal information of the ALP-induced photon signal, and use the Fermi-LAT observations of GW170817 to derive our new ALP constraints. We also show the improved prospects with future MeV gamma-ray missions, taking the spectral and temporal coverage of Fermi-LAT as an example.

Figures (9)

• Figure 1: An artist's rendition of our main idea. The ALP (dashed line), after being produced in the NS merger, escapes and decays outside the merger environment into photons, which can be detected by the Fermi satellite (or future MeV gamma-ray telescopes).
• Figure 2: ALP production spectrum from a merger remnant, assuming constant emission for one second and for $g_{a\gamma\gamma}=10^{-10}\,\text{GeV}^{-1}$. Note the switchover between Primakoff and photon coalescence at $m_a \approx 100\,\text{MeV}$.
• Figure 3: Temporal (top panels) and spectral (bottom panels) behaviors of the photon flux coming from ALP decays. The left panels correspond to Benchmark 1 (shorter-lived ALPs with $m_a = 398 \, {\rm MeV}$ and $g_{a\gamma\gamma} = 5.01 \times 10^{-11}\, {\rm GeV}^{-1}$), whereas the right panels correspond to Benchmark 2 (longer-lived ALPs with $m_a = 200 \, {\rm MeV}$ and $g_{a\gamma\gamma} = 1.41 \times 10^{-12} \,{\rm GeV}^{-1}$). The colored contours correspond to various spectral (top panels) and temporal (bottom panels) snap shots.
• Figure 4: Exclusion and sensitivity contours in the $(m_a,g_{a\gamma\gamma})$ plane; see text for details. The red square and purple triangle correspond, respectively, to Benchmarks 1 and 2 in Fig. \ref{['timedepmain']}.
• Figure S1: Feynman diagrams for the Primakoff $\gamma + p \rightarrow a + p$ (left) and photon coalescence $\gamma + \gamma \rightarrow a$ (right) processes.