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Register a new userSearching for spectral oscillations due to photon-axionlike particle conversion using the Fermi-LAT observations of bright supernova remnants
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Axionlike-particles (ALPs) are one promising type of dark matter candidate particle that may generate detectable effects on $gamma$-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 $gamma$-ray spectrum of IC443, which gives a statistical significance of $4.2sigma$ in favor of such spectral oscillation. However, the best-fit parameters of ALPs ($m_{a}=6.6,{rm neV}$, $g_{agamma}=13.4 times 10^{-11},{rm GeV}^{-1}$) are in tension with the upper bound ($g_{agamma}< 6.6 times 10^{-11},{rm GeV}^{-1}$) 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.
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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, ie. IC443, W51C and W49B) have been adopted together to search such the 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 inconsistence 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 the 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.
We report the detection of gamma-ray emission coincident with four supernova remnants (SNRs) using data from the Large Area Telescope on board the Fermi Gamma-ray Space Telescope. G349.7+0.2, CTB 37A, 3C 391 and G8.7-0.1 are supernova remnants known to be interacting with molecular clouds, as evidenced by observations of hydroxyl (OH) maser emission at 1720 MHz in their directions. SNR shocks are expected to be sites of cosmic rays acceleration, and clouds of dense material can provide effective targets for production of gamma-rays from pion-decay. The observations reveal unresolved sources in the direction of G349.7+0.2, CTB 37A and 3C 391, and a possibly extended source coincident with G8.7-0.1, all with significance levels greater than 10 sigma.
We report detection of a line-like feature in the $gamma$-ray spectrum of the blazar B0516$-$621, for which the data obtained with the Large Area Telescope onboard {it Fermi Gamma-Ray Space Telescope (Fermi)} are analyzed. The feature is at $sim$7,GeV and different analyses are conducted to check its real presence. We determine that it has a significance of 2.5--3.0$sigma$, and cautiously note the presence of possible systematics in the data which could reduce the significance. This putative feature is too narrow to be explained with radiation processes generally considered for jet emission of blazars. Instead, it could be a signal due to the oscillations between photons and axion-like particles (ALPs) in the sources jet. We investigate this possibility by fitting the spectrum with the photon-ALP oscillation model, and find that the parameter space of ALP mass $m_aleq 10^{-8}$,eV and the coupling constant (between photons and ALPs) $g_{agamma}$=1.16--1.48$times 10^{-10}$,GeV$^{-1}$ can provide a fit to the line-like feature, while the magnetic field at the emission site of $gamma$-rays is fixed at 0.7,G. The ranges for $m_a$ and $g_{agamma}$ are in tension with those previously obtained from several experiments or methods, but on the other hand in line with some of the others. This spectral-feature case and its possible indication for ALP existence could be checked from similar studies of other blazar systems and also suggest a direction of effort for building future high-energy facilities that would have high sensitivities and spectral resolutions for searching for similar features.
The Fermi $gamma$-ray space telescope reported the observation of several Galactic supernova remnants recently, with the $gamma$-ray spectra well described by hadronic $pp$ collisions. The possible neutrino emissions from these Fermi detected supernova remnants are discussed in this work, assuming the hadronic origin of the $gamma$-ray emission. The muon event rates induced by the neutrinos from these supernova remnants on typical km$^3$ neutrino telescopes, such as the IceCube and the KM3NeT, are calculated. The results show that for most of these supernova remnants the neutrino signals are too weak to be detected by the on-going or up-coming neutrino experiment. Only for the TeV bright sources RX J1713.7-3946 and possibly W28 the neutrino signals can be comparable with the atmospheric background in the TeV region, if the protons can be accelerated to very high energies. The northern hemisphere based neutrino telescope might detect the neutrinos from these two sources.
Axionlike particles (ALPs) are a common prediction of theories beyond the Standard Model of particle physics that could explain the entirety of the cold dark matter. These particles could be detected through their mixing with photons in external electromagnetic fields. Here, we provide a short review over ALP searches that utilize astrophysical $gamma$-ray observations. We summarize current bounds as well as future sensitivities and discuss the possibility that ALPs alter the $gamma$-ray opacity of the Universe.
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