Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userSearching for the possible signal of the photon-axionlike particle oscillation in the combined GeV and TeV spectra of supernova remnants
223
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
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.
rate research
Read More
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.
The emission mechanism for hard $gamma$-ray spectra from supernova remnants (SNRs) is still a matter of debate. Recent multi-wavelength observations of TeV source HESS J1912+101 show that it is associated with an SNR with an age of $sim 100$ kyrs, making it unlikely produce the TeV $gamma$-ray emission via leptonic processes. We analyzed Fermi observations of it and found an extended source with a hard spectrum. HESS J1912+101 may represent a peculiar stage of SNR evolution that dominates the acceleration of TeV cosmic rays. By fitting the multi-wavelength spectra of 13 SNRs with hard GeV $gamma$-ray spectra with simple emission models with a density ratio of GeV electrons to protons of $sim 10^{-2}$, we obtain reasonable mean densities and magnetic fields with a total energy of $sim 10^{50}$ ergs for relativistic ions in each SNR. Among these sources, only two of them, namely SN 1006 and RCW 86, favor a leptonic origin for the $gamma$-ray emission. The magnetic field energy is found to be comparable to that of the accelerated relativistic ions and their ratio has a tendency of increase with the age of SNRs. These results suggest that TeV cosmic rays mainly originate from SNRs with hard $gamma$-ray spectra.
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.
We calculate the energy spectra of cosmic rays (CR) and their secondaries produced in a supernova remnant (SNR), taking into account the time-dependence of the SNR shock. We model the trajectories of charged particles as a random walk with a prescribed diffusioncoefficient, accelerating the particles at each shock crossing. Secondary production by CRs colliding with gas is included as a Monte Carlo process. We find that SNRs produce less antimatter than suggested previously: The positron/electron ratio and the antiproton/proton ratio are a few percent and few $times 10^{-5}$, respectively. Both ratios do not rise with energy.
Supernova remnants have long been regarded as sources of the Galactic cosmic rays up to petaelectronvolts, but convincing evidence is still lacking. In this work we explore the common origin of the subtle features of the cosmic ray spectra, such as the knee of cosmic ray spectra and the excesses of electron/positron fluxes recently observed by ATIC, H.E.S.S., Fermi-LAT and PAMELA. Numerical calculation shows that those features of cosmic ray spectra can be well reproduced in a scenario with e$^+$e$^-$ pair production by interactions between high energy cosmic rays and background photons in an environment similar to the young supernova remnant. The success of such a coherent explanation serves in turn as an evidence that at least a portion of cosmic rays might be accelerated at young supernova remnants.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
