The Origin of Gamma-Rays from Globular Clusters

Fermi has detected gamma-ray emission from eight globular clusters. We suggest that the gamma-ray emission from globular clusters may result from the inverse Compton scattering between relativistic electrons/positrons in the pulsar wind of MSPs in the globular clusters and background soft photons including cosmic microwave/relic photons, background star lights in the clusters, the galactic infrared photons and the galactic star lights. We show that the gamma-ray spectrum from 47 Tuc can be explained equally well by upward scattering of either the relic photons, the galactic infrared photons or the galactic star lights whereas the gamma-ray spectra from other seven globular clusters are best fitted by the upward scattering of either the galactic infrared photons or the galactic star lights. We also find that the observed gamma-ray luminosity is correlated better with the combined factor of the encounter rate and the background soft photon energy density. Therefore the inverse Compton scattering may also contribute to the observed gamma-ray emission from globular clusters detected by Fermi in addition to the standard curvature radiation process. Furthermore, we find that the emission region of high energy photons from globular cluster produced by inverse Compton scattering is substantially larger than the core of globular cluster with a radius >10pc. The diffuse radio and X-rays emitted from globular clusters can also be produced by synchrotron radiation and inverse Compton scattering respectively. We suggest that future observations including radio, X-rays, and gamma-rays with energy higher than 10 GeV and better angular resolution can provide better constraints for the models.Comment: Accepted by ApJ, Comments may send to Prof. K.S. Cheng: [email protected]

Analysis of Microstrip Lines with Alternative Implementation of Conductors and Superconductors

An analysis of microstrip line structures in which either the strip or the ground plane or both are made of a high Tc superconductor is presented. The effect of implementation of a superconductor to the strip and the ground plane is explained with the calculation of a conductor loss of the structure by the Phenomenological Loss Equivalence Method (PEM). The theoretical values are compared with the experimental results from a ring resonator which is made of a gold ground plane and a high Tc superconductor, YBa2Cu3O(7-x), strip

A Detailed Analysis of One-loop Neutrino Masses from the Generic Supersymmetric Standard Model

In the generic supersymmetric standard model which had no global symmetry enforced by hand, lepton number violation is a natural consequence. Supersymmetry, hence, can be considered the source of experimentally demanded beyond standard model properties for the neutrinos. With an efficient formulation of the model, we perform a comprehensive detailed analysis of all one-loop contributions to neutrino masses.Comment: 27 pages Revtex, no figur

The Fundamental Plane of Gamma-ray Globular Clusters

We have investigated the properties of a group of $\gamma$-ray emitting globular clusters (GCs) which have recently been uncovered in our Galaxy. By correlating the observed $\gamma$-ray luminosities $L_{\gamma}$ with various cluster properties, we probe the origin of the high energy photons from these GCs. We report $L_{\gamma}$ is positively correlated with the encounter rate $\Gamma_{c}$ and the metalicity $\left[{\rm Fe/H}\right]$ which place an intimate link between the gamma-ray emission and the millisecond pulsar population. We also find a tendency that $L_{\gamma}$ increase with the energy densities of the soft photon at the cluster location. Furthermore, the two-dimensional regression analysis suggests that $L_{\gamma}$, soft photon densities, and $\Gamma_{c}$/$\left[{\rm Fe/H}\right]$ possibly span fundamental planes which potentially provide better predictions for the $\gamma$-ray properties of GCs.Comment: 17 pages, 4 figures, 3 tables, published in Ap

Gamma-ray emission from the globular clusters Liller 1, M80, NGC 6139, NGC 6541, NGC 6624, and NGC 6752

Globular clusters (GCs) are emerging as a new class of gamma-ray emitters, thanks to the data obtained from the Fermi Gamma-ray Space Telescope. By now, eight GCs are known to emit gamma-rays at energies >100~MeV. Based on the stellar encounter rate of the GCs, we identify potential gamma-ray emitting GCs out of all known GCs that have not been studied in details before. In this paper, we report the discovery of a number of new gamma-ray GCs: Liller 1, NGC 6624, and NGC 6752, and evidence for gamma-ray emission from M80, NGC 6139, and NGC 6541, in which gamma-rays were found within the GC tidal radius. With one of the highest metallicity among all GCs in the Milky Way, the gamma-ray luminosity of Liller 1 is found to be the highest of all known gamma-ray GCs. In addition, we confirm a previous report of significant gamma-ray emitting region next to NGC 6441. We briefly discuss the observed offset of gamma-rays from some GC cores. The increasing number of known gamma-ray GCs at distances out to ~10 kpc is important for us to understand the gamma-ray emitting mechanism and provides an alternative probe to the underlying millisecond pulsar populations of the GCs.Comment: 22 pages, 7 figures, 2 tables; ApJ, in pres

NuSTAR observations and broadband spectral energy distribution modeling of the millisecond pulsar binary PSR J1023+0038

We report the first hard X-ray (3-79 keV) observations of the millisecond pulsar (MSP) binary PSR J1023+0038 using NuSTAR. This system has been shown transiting between a low-mass X-ray binary (LMXB) state and a rotation-powered MSP state. The NuSTAR observations were taken in both LMXB state and rotation-powered state. The source is clearly seen in both states up to ~79 keV. During the LMXB state, the 3-79 keV flux is about a factor of 10 higher that in the rotation-powered state. The hard X-rays show clear orbital modulation during the X-ray faint rotation-powered state but the X-ray orbital period is not detected in the X-ray bright LMXB state. In addition, the X-ray spectrum changes from a flat power-law spectrum during the rotation-powered state to a steeper power-law spectrum in the LMXB state. We suggest that the hard X-rays are due to the intra-binary shock from the interaction between the pulsar wind and the injected material from the low-mass companion star. During the rotation-powered MSP state, the X-ray orbital modulation is due to Doppler boosting of the shocked pulsar wind. At the LMXB state, the evaporating matter of the accretion disk due to the gamma-ray irradiation from the pulsar stops almost all the pulsar wind, resulting the disappearance of the X-ray orbital modulation.Comment: 8 pages, 6 figures; accepted for publication in Ap

Multi-wavelength emissions from the millisecond pulsar binary PSR J1023+0038 during an accretion active state

Recent observations strongly suggest that the millisecond pulsar binary PSR J1023+0038 has developed an accretion disk since 2013 June. We present a multi-wavelength analysis of PSR J1023+0038, which reveals that 1) its gamma-rays suddenly brightened within a few days in June/July 2013 and has remained at a high gamma-ray state for several months; 2) both UV and X-ray fluxes have increased by roughly an order of magnitude, and 3) the spectral energy distribution has changed significantly after the gamma-ray sudden flux change. Time variabilities associated with UV and X-rays are on the order of 100-500 seconds and 50-100 seconds, respectively. Our model suggests that a newly formed accretion disk due to the sudden increase of the stellar wind could explain the changes of all these observed features. The increase of UV is emitted from the disk, and a new component in gamma-rays is produced by inverse Compton scattering between the new UV component and pulsar wind. The increase of X-rays results from the enhancement of injection pulsar wind energy into the intra-binary shock due to the increase of the stellar wind. We also predict that the radio pulses may be blocked by the evaporated winds from the disk and the pulsar is still powered by rotation.Comment: 8 pages, 3 figures; accepted for publication in Ap