Searching for spectral oscillations due to photon-axionlike particle conversion using the Fermi-LAT observations of bright supernova remnants

Abstract

Axionlike-particles (ALPs) are one promising type of dark matter candidate particle that may generate detectable effects on γ-ray spectra other than the canonical weakly interacting massive particles. In this work we search for such oscillation effects in the spectra of supernova remnants caused by the photon-ALP conversion, using the Fermi Large Area Telescope data. Three bright supernova remnants, IC443, W44, and W51C, are analyzed. The inclusion of photon-ALP oscillations yields an improved fit to the γ-ray spectrum of IC443, which gives a statistical significance of 4.2σ in favor of such spectral oscillation. However, the best-fit parameters of ALPs (ma = 6.6 neV, gaγ = 13.4 × 10 −11 GeV −1 ) are in tension with the upper bound (gaγ < 6.6 × 10 −11 GeV −1 ) set by the CAST experiment. It is difficult to explain the results using the systematic uncertainties of the flux measurements. We speculate that the "irregularity" displayed in the spectrum of IC443 may be due to the superposition of the emission from different parts of the remnant.PACS numbers: 95.35.+d, 95.85.Pw, 98.58.Mj

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

“…The current result is inconsistent with our pervious work [32] which solely analyzed the Fermi-LAT spectrum of IC443 with the P8R2 data and the 3FGL catalog [55]. Our pervious work [32] gave the TS value ∼ 20.8 (4.2σ) at the favored parameters (m a , g aγ ) = (6.7 neV, 20.2 × 10 −11 GeV −1 ) for Bfield1. Such parameters however are strongly excluded by the current data.…”

“…In our pervious work [32], the Fermi-LAT spectrum of IC443 obtained with the P8R2 data and 3FGL showed a preference for the ALP model at the best-fit parameters (m a , g aγ ) = (6.7 neV, 20.2 × 10 −11 GeV −1 ) corresponding to a TS value ∼ 20.8 (Bfield1). However, with these best-fit parameters, the ALP model don't give any improvement to the fit of the joint Fermi+MAGIC+VERITAS spectrum of IC443 in this work.…”

“…The large-scale Galactic magnetic field model developed by Jansson & Farrar [51] (Bfield1) is adopted in our work, which has been wildly used in the relevant investigations [29][30][31][32][33]. This model composes of a disk field, an extended halo field and out of plane component and provides a best fit to WMAP7 Galactic synchrotron emission map and more than 40,000 extragalactic rotation measures (RM) data.…”

“…Besides, the conversion between γ-ray photons and ALPs in external magnetic fields could create energy-dependent modulations in spectra of γ-ray sources, which is so called the photon-ALP oscillation. Such a spectral oscillation effect could be a smoking-gun signature for the existence of ALPs [16][17][18][19][20][21] and has been widely used to search for ALP signals [22][23][24][25][26][27][28][29][30][31][32][33]. The Fermi-LAT Collaboration have searched for the photon-ALP oscillation signal in the High Energy (HE) spectrum of NGC 1275 and excluded the coupling g aγ above 5×10 −11 GeV −1 for ALP masses 0.5−5 neV [26].…”

“…Collaboration [23] and Zhang et al [28] without significant signal of ALPs found. The γ-ray spectra of bright pulsars [29][30][31] and SNRs [32] obtained from the Fermi-LAT data show intriguing indications for the photon-ALP oscillation, but the best-fit parameters are in tension with the limit from the CAST helioscope. Besides, Liang et al found that higher ALP mass region of the ALP parameter space can be probed by the H.E.S.S.…”