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Pulsar halos (also termed "TeV halos") are a new class of γ -ray sources in the Galaxy, which manifest as extended γ -ray emission around middle-aged pulsars, as discovered around the Geminga pulsar, the Monogem pulsar, and PSR J0622+3749 by the High-Altitude Water Cherenkov Observatory and the Large High-Altitude Air Shower Observatory. A consensus has been reached that the teraelectronvolt emission comes from the inverse Compton scattering of escaping electrons/positrons from the pulsar wind nebula of the soft background radiation field, while the particle transport mechanism in the halo is still in dispute. Currently, there are mainly three interpretations: the isotropic, suppressed diffusion model; the isotropic, unsuppressed diffusion model that considers the ballistic propagation of newly injected particles; and the anisotropic diffusion model. While the predicted γ -ray surface brightness profiles of all three models can be more or less consistent with the observations, the implications of the three models for cosmic-ray transport mechanisms and the properties of the interstellar magnetic field are quite different. In this study, we calculate the anticipated X-ray emission of pulsar halos under the three models. We show that the synchrotron radiation of these escaping electrons/positrons can produce a corresponding X-ray halo around the pulsar and that the expected surface brightness profiles are distinct in the three models. We suggest that sensitive X-ray detectors of a large field of view (such as eROSITA and the Einstein Probe) with a reasonably long exposure time are crucial to understanding the formation mechanism of pulsar halos and can serve as a probe of the properties of interstellar turbulence. [ABSTRACT FROM AUTHOR]

Finite elements methods are used to investigate the thermal-electrical characteristics of gallium-nitride (GaN) light-emitting diodes (LEDs) with different transparent conductive layers (TCLs) and buried depths of electrodes, where the transparent conductive layers include indium tin oxide (ITO), graphene (Gr) and the combination of them (ITO/Gr). The optimal material parameters and the precision and accuracy of the simulation model are validated. Moreover, the parameters' sensitivity analysis is carried out as well. The results indicate that the LED with the TCL of a 100-nm ITO or 4-layer Gr has a good thermal-electrical performance from the viewpoint of the maximum temperature and the current density deviation of multiple quantum well (MQW), where the maximum temperature occurs at the n-Pad rather than p-Pad. The compound TCL with a 20-nm ITO and 3-layer Gr reaches a thermal-electrical performance better than that of a 100-nm ITO or 4-layer Gr. Moreover, their maximum temperatures decrease about −0.43% and 1.21%, and the current density uniformities increase up to −6.09% and 17.41%, respectively. Furthermore, when the electrode buried depth is 0.51 μm, the thermal-electrical performance of the GaN LEDs can be further improved. [ABSTRACT FROM AUTHOR]

Pulsar halos (also termed “TeV halos”) are a new class of γ -ray sources in the Galaxy, which manifest as extended γ -ray emission around middle-aged pulsars, as discovered around the Geminga pulsar, the Monogem pulsar, and PSR J0622+3749 by the High-Altitude Water Cherenkov Observatory and the Large High-Altitude Air Shower Observatory. A consensus has been reached that the teraelectronvolt emission comes from the inverse Compton scattering of escaping electrons/positrons from the pulsar wind nebula of the soft background radiation field, while the particle transport mechanism in the halo is still in dispute. Currently, there are mainly three interpretations: the isotropic, suppressed diffusion model; the isotropic, unsuppressed diffusion model that considers the ballistic propagation of newly injected particles; and the anisotropic diffusion model. While the predicted γ -ray surface brightness profiles of all three models can be more or less consistent with the observations, the implications of the three models for cosmic-ray transport mechanisms and the properties of the interstellar magnetic field are quite different. In this study, we calculate the anticipated X-ray emission of pulsar halos under the three models. We show that the synchrotron radiation of these escaping electrons/positrons can produce a corresponding X-ray halo around the pulsar and that the expected surface brightness profiles are distinct in the three models. We suggest that sensitive X-ray detectors of a large field of view (such as eROSITA and the Einstein Probe) with a reasonably long exposure time are crucial to understanding the formation mechanism of pulsar halos and can serve as a probe of the properties of interstellar turbulence.