The measurement of an excess in the cosmic-ray electron spectrum between 300 and 800 GeV by the ATIC experiment has - together with the PAMELA detection of a rise in the positron fraction up to 100 GeV - motivated many interpretations in terms of dark matter scenarios; alternative explanations assume a nearby electron source like a pulsar or supernova remnant. Here we present a measurement of the cosmic-ray electron spectrum with H.E.S.S. starting at 340 GeV. While the overall electron flux measured by H.E.S.S. is consistent with the ATIC data within statistical and systematic errors, the H.E.S.S. data exclude a pronounced peak in the electron spectrum as suggested for interpretation by ATIC. The H.E.S.S. data follow a power-law spectrum with spectral index of 3.0 +- 0.1 (stat.) +- 0.3 (syst.), which steepens at about 1 TeV.
The data recently obtained by PAMELA and ATIC show the presence of the peak in the cosmic positron spectrum at energies above 100 GeV. In this paper it has been shown that the peak can arise due to processes of the interaction of cosmic rays with neutralino dark matter, which are accompanied by chargino production and its leptonic decay.
A strong excess in a form of a wide peak in the energy range of 300-800 GeV was discovered in the first measurements of the electron spectrum in the energy range from 20 GeV to 3 TeV by the balloon-borne experiment ATIC (J. Chang et al. Nature, 2008). The experimental data processing and analysis of the electron spectrum with different criteria for selection of electrons, completely independent of the results reported in (J. Chang et al. Nature, 2008) is employed in the present paper. The new independent analysis generally confirms the results of (J. Chang et al. Nature, 2008), but shows that …
Motivated by a two-bump (or 1-peak plus 1-hump) structure in the ATIC data, we perform a statistical analysis fitting the PAMELA and ATIC data to a dark matter model, in which the dark matter particle can undergo both annihilation and decay. Using a chi-square analysis we show that both data can be simultaneously fitted better with such a double-action dark matter particle. We use an existing neutrino mass model in literature to illustrate the idea.
Curvature effects in Gamma-ray bursts (GRBs) have long been a source of considerable interest. In a collimated relativistic GRB jet, photons that are off-axis relative to the observer arrive at later times than on-axis photons and are also expected to be spectrally softer. In this work, we invoke a relatively simple kinematic two-shell collision model for a uniform jet profile and compare its predictions to GRB prompt-emission data for observations that have been attributed to curvature effects such as the peak-flux--peak-frequency relation, i.e., the relation between the $ν$F$_ν$ flux and the…
An analysis is made of the fine structure in the cosmic ray energy spectrum: new facets of present observations and their interpretation and the next step. It is argued that less than about 10% of the intensity of the helium `peak' at the knee at $\simeq 5PeV$ is due to just a few sources (SNR) other than the single source. The apparent concavity in the rigidity spectra of protons and helium nuclei which have maximum curvature at about 200 GV is confirmed by a joint analysis of the PAMELA, CREAM and ATIC experiments. The spectra of heavier nuclei also show remarkable structure in the form of `…
We investigate the observed spectrum of cosmic-ray electrons and positrons from astrophysical sources, especially pulsars, and the physical processes for making the spectrum spiky or smooth via continuous and multiple electron/positron injections. We find that (1) the average electron spectrum predicted from nearby pulsars are consistent with PAMELA, Fermi and H.E.S.S. data. However, the ATIC/PPB-BETS peak around 500GeV is hard to produce by the sum of multiple pulsar contributions and requires a single (or a few) energetic pulsar(s). (2) A continuous injection produces a broad peak and a high…
Recent kinetic simulations sparked a debate regarding the emission mechanism responsible for pulsed GeV $γ$-ray emission from pulsars. Some models invoke curvature radiation, while other models assume synchrotron radiation in the current-sheet. We interpret the curved spectrum of the Vela pulsar as seen by H.E.S.S. II (up to $\sim$100 GeV) and the $Fermi$ Large Area Telescope (LAT) to be the result of curvature radiation due to primary particles in the pulsar magnetosphere and current sheet. We present phase-resolved spectra and energy-dependent light curves using an extended slot gap and curr…
Particle acceleration is expected to be different between relativistic and non-relativistic collisionless shocks. We show that electromagnetic counterparts to gravitational waves (GWs), gamma-ray burst (GRB) afterglows, are ideal targets for observing trans-relativistic evolution of accelerated electron distribution because the GWs spot nearby GRBs with off-axis jets, otherwise missed in gamma-ray observations. We find that the relativistic spectral slope begins to change steeply near the peak time of the light curve and approaches the non-relativistic limit in about 10 times the peak time. Th…
Even with several thousand {\it Fermi}-LAT blazar detections, the $γ$-ray emission mechanism is poorly understood. We explore correlated optical/$γ$-ray flux variations for 178 {\it Fermi}-LAT blazars regularly monitored by KAIT, SMARTS, and the Steward Observatory. Out of the 178 sources, 121 show a measurable ($>1σ$) discrete correlation function peak. Using the derived time-lags and Bayesian block light-curve decompositions, we measure the fraction of common and orphan flares between the two bands. After accounting for sampling and sensitivity limitations we quantify for the first time the …
We have used single-dish centimeter-band, multi-frequency linear polarization and total flux density monitoring observations obtained by UMRAO at 14.5, 8, and 4.8 GHz during gamma-ray flaring to constrain propagating shock-in-jet models; this procedure allows us to probe jet conditions at or near the presumed parsec-scale gamma-ray emission site within the relativistic jet. Results are presented for the blazar 0420-014 during the gamma-ray flare detected by the LAT which peaked in late January 2010. Our work identifies the passage of three forward-moving transverse shocks during the radio-band…
Vela X-1 is among the best studied and most luminous accreting X-ray pulsars. The supergiant optical companion produces a strong radiatively-driven stellar wind, which is accreted onto the neutron star producing highly variable X-ray emission. A complex phenomenology, due to both gravitational and radiative effects, needs to be taken into account in order to reproduce orbital spectral variations. We have investigated the spectral and light curve properties of the X-ray emission from Vela X-1 along the binary orbit. These studies allow to constrain the stellar wind properties and its perturbati…
We study the spectrum of cosmic ray positrons produced by a scaling distribution of non-superconducting cosmic strings. In this scenario, the positrons are produced from the jets which form from the cosmic string cusp annihilation process. The spectral shape is a robust feature of our scenario, and is in good agreement with the results from the recent PAMELA and ATIC experiments. In particular, the model predicts a sharp upper cutoff in the spectrum, and a flux which rises as the upper cutoff is approached. The energy at which the flux peaks is determined by the initial jet energy. The amplitu…
X-ray polarimetry promises us an unprecedented look at the structure of magnetic fields and on the processes at the base of acceleration of particles up to ultrarelativistic energies in relativistic jets. Crucial pieces of information are expected from observations of blazars (that are characterized by the presence of a jet pointing close to the Earth), in particular of the subclass defined by a synchrotron emission extending to the X-ray band (so-called high synchrotron peak blazars, HSP). In this review, I give an account of some of the models and numerical simulations developed to predict t…
Measuring high energy cosmic ray electrons/positrons (CRE) provides important means for the dark matter (DM) indirect detection and for probing the nearby galactic sources. In this work, we perform a systematic analysis of the flavor structure of DM annihilations into charged leptons based on the cosmic ray CRE spectra measured by DAMPE, Fermi-LAT, AMS-02, and CALET experiments. We study the annihilations of possible TeV scale DM particles in a nearby subhalo, which is proposed to explain the possible peak-like structure of the DAMPE CRE data. We pay special attention to the possible non-reson…
Probing Planck-Scale Physics with High-Frequency Gravitational Waves
University of California, Santa Cruz（加州大学圣克鲁兹分校）；Santa Cruz Institute for Particle Physics, University of California, Santa Cruz（加州大学圣克鲁兹分校圣克鲁兹粒子物理研究所）
