Searching for the possible signal of the photon-axionlike particle oscillation in the combined GeV and TeV spectra of supernova remnants

The conversion between photons and axionlike particles (ALPs) in the Milky Way magnetic field could result in the detectable oscillation phenomena in $\gamma$-ray spectra of Galactic sources. In this work, the GeV (Fermi-LAT) and TeV (MAGIC/VERITAS/H.E.S.S.) data of three bright supernova remnants (SNRs), i.e., IC443, W51C, and W49B, have been adopted together to search for such an oscillation effect. Different from our previous analysis of the sole Fermi-LAT data of IC443, we do not find any reliable signal for the photon-ALP oscillation in the joint broadband spectrum of each SNR. The reason for the inconsistency is that in this work we use the latest revision (P8R3) of Fermi-LAT data, updated diffuse emission templates, and the new version of the source catalog (4FGL), which lead to some modification of the GeV spectrum of IC443. Then we set constraints on ALP parameters based on the combined analysis of all three sources. Though these constraints are somewhat weaker than limits from the CAST experiment and globular clusters, they are supportive of and complementary to these other results.

Figure 1

Survival probabilities $P_{\mathrm{ALP}}$ for photons from IC443 with five different sets of parameters (Bfield1).

Figure 2

Left panel: The TS value as a function of ALP mass $m_a$ and photon-ALP coupling constant $g_{a\gamma }$ for IC443 ($\mathrm{Fermi}+\mathrm{MAGIC}+\mathrm{VERITAS}$, Bfield1). The upper boundary of the color bar scale is set as the ${\mathrm{TS}}_{\max }$ in the scanning, while the lower one is $-6.2$. The black dashed lines show the upper limit of the photon-ALP coupling set by CAST [13]. Right panel: The joint broadband spectrum and the best-fit models without and with photon-ALP oscillations. The ${\mathrm{TS}}_{\mathrm{i}}={\chi }_{\mathrm{w}/\mathrm{o}\mathrm{ALP},\mathrm{i}}^2-{\chi }_{\mathrm{w}\mathrm{ALP},\mathrm{i}}^2$ (gray curve) demonstrates the contribution of each data point to the total TS value for the best-fit ALP model.

Figure 3

Left panel: The TS value as a function of ALP mass $m_a$ and photon-ALP coupling constant $g_{a\gamma }$ for W51C ($\mathrm{Fermi}+\mathrm{MAGIC}$, Bfield1). Right panel: The joint broadband spectrum of W51C and the best-fit models without and with photon-ALP oscillations.

Figure 4

Left panel: The TS value as a function of ALP mass $m_a$ and photon-ALP coupling constant $g_{a\gamma }$ for W49B ($\mathrm{Fermi}+\mathrm{H}.\mathrm{E}.\mathrm{S}.\mathrm{S}.$, Bfield1). Right panel: The joint broadband spectrum of W49B and the best-fit models without and with photon-ALP oscillations.

Figure 5

The TS distribution of the null hypothesis for the ALP analysis. The histogram is from 500 Monte Carlo simulations of spectra with the null hypothesis. The dashed curve is the best-fit ${\chi }^2$ distribution with degrees of freedom $d=4.6\pm 0.1$. The red vertical line shows the threshold value corresponding to a 95% confidence level based on the best-fit distribution.

Figure 6

The TS distribution for the coverage test with 500 simulations of spectra with the injected ALP signal $(m_a,g_{a\gamma })=(10\mathrm{neV},50\times {10}^{-11}{\mathrm{GeV}}^{-1})$.

Figure 7

The 95% confidence level limits on ALP parameters by combining all three SNRs. The red region is obtained from Bfield1. The dashed lines are for two additional magnetic field models Bfield2 (green) and Bfield3 (blue), respectively. The black star $(m_a,g_{a\gamma })=(3.6\mathrm{neV},23\times {10}^{-11}{\mathrm{GeV}}^{-1})$ are the best-fit ALP parameters of the possible photon-ALPs mixing signal found by Majumdar et al. with the Jansson and Farrar (Bfield1) GMF model in Ref. [34].

Figure 8

Left panel: The TS value as a function of ALP mass $m_a$ and photon-ALP coupling constant $g_{a\gamma }$ for IC443 (Fermi, Bfield1). Right panel: The Fermi-LAT spectrum of IC443 and the best-fit models without and with photon-ALP oscillations.