Constraints on axion-like particle properties with TeV gamma-ray observations of Galactic sources

Abstract

Axion-like particles (ALPs) can oscillate to photons and vice versa in electromagnetic fields. The photon-ALP oscillation provides an attractive solution to the apparent transparency of the Universe to TeV photons. The allowed parameter regions for the ALP mass m a ≤ 10 −7 eV have been tightly constrained by the Fermi-LAT and H.E.S.S observations of some extragalactic sources. In this work we show for the first time that the H.E.S.S observations of some TeV sources in the Galactic plane exclude the highest ALP mass region (i.e., m a ∼ a few × 10 −7 eV) that accounts for the TeV transparency of the Universe. The upcoming CTA observations of the Galactic TeV sources are shown to be able to improve the constraints significantly. PACS numbers: 95.35.+d, 95.85.Pw

On the impact of magnetic-field models in galaxy clusters on constraints on axion-like particles from the lack of irregularities in high-energy spectra of astrophysical sources

“…[52], Faraday rotation mapping of the Perseus cluster looks a promising way to obtain better constraints on the magnetic field in the region where the lobes of NGC 1275 interact with the intracluster matter. In addition, sources embedded in magnetic fields better studied observationally may be invoked for the search of irregularities, for instance M 87 [39] and Galactic sources [32,33,34]. For certain values of ALP parameters, the transition to the regime of strong mixing in the Galactic magnetic field may be observed or constrained also for extragalactic sources, cf.…”

“…Several attempts to follow this way have been made in recent years, exploiting the observed smoothness of X-and gammaray spectra of strong emitters presumably embedded in astrophysical magnetic fields. In particular, these included analyses of gamma-ray observations of PKS 2155−304 [27,28,29], NGC 1275 [30,31] and several Galactic sources [32,33,34] relevant for ALP masses ∼ 10 −9 − 10 −7 eV (overlapping with the range invoked for explanations of the "anomalous transparency" effects). For lower ALP masses, X-ray observations of 3C 218 [35], the same NGC 1275 [36,37,38], M 87 [39] and some other extragalactic sources [40] were used.…”

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

“…By summing the ∆χ 2 value of all the three SNRs, we derive combined constraints on ALP parameters. Some studies [26,33] have shown that, due to the complexity between ALP parameters and spectral irregularities, the ∆χ 2 distribution in the null hypothesis is not as expected by Wilks theorem [65] to be a χ 2 distribution with 2 degree of freedom. We thus perform Monte Carlo (MC) simulation to derive the null distribution and the threshold value of ∆χ 2 .…”

“…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].…”