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Significant flares of GeV γ-ray emission from the Crab Nebula were found by AGILE and Fermi-LAT years ago, indicating that extreme particle acceleration and radiation occurs in young pulsar wind nebulae. To enlarge the flare sample and to investigate their statistical properties will be very useful in understanding the nature of the γ-ray flares. In this paper, we investigate the flaring emission from the Crab Nebula with eleven year observations of the Fermi-LAT. We identify 17 significant flares in the light curve of the low-energy (synchrotron) component of the γ-ray emission. The flare rate is about 1.5 per year, without any significant change or clustering during the 11 years of the observation. We detect a special flare with an extremely long duration of nearly one month, that occurred in 2018 October, with synchrotron photons up to energies of about 1 GeV. The synchrotron component could be fitted by a steady power-law (PL) background and a variable flare component with an exponentially cutoff PL spectrum, not only for the individual flare but also for the combined data, which may favor a similar emission mechanism for all flares. However, we do not find a universal relation between the cutoff energy and the energy fluxes of the flares, which may reflect the complicated acceleration and/or cooling processes of the involved particles. [ABSTRACT FROM AUTHOR]

Complex magnetically insulated transmission line oscillator (MILO), as an important development direction, can enhance the power efficiency and generate dual-band high power microwaves (HPMs). A complex MILO and a preliminary dual-band radiation system have been proposed in our previous studies. However, the axial length of the dual-band radiation system is too long to meet the compact requirements. In this paper, a compact dual-band radiation system is presented and investigated numerically. The compact dual-band radiation system comprises a dual-band cross-shaped mode converter and a dual-band coaxial conical horn antenna. It can convert two coaxial TEM mode microwaves (1.717 GHz and 4.167 GHz) generated by the complex MILO into the coaxial TE11 mode microwaves, and then radiate them into the air. At 1.717 GHz, the gain of the antenna is 17.9 dB, and the total return loss and diffraction loss are 1.50% and 0, respectively. At 4.167 GHz, the gain is 19.4 dB, and the total return loss and diffraction loss are 1.17% and 0.78%, respectively. The power handling capacity of the antenna is 5.1 GW at 1.717 GHz and 2.0 GW at 4.167 GHz. Comparing with the original structure, the length of the dual-band radiation system is reduced by 45.2%. [ABSTRACT FROM AUTHOR]

Gamma-ray bursts (GRBs) are empirically classified as long-duration GRBs (LGRBs, >2 s) and short-duration GRBs (SGRBs, <2 s). Physically they can be grouped into two distinct progenitor categories: those originating from collapse of massive stars (also known as Type II) and those related to mergers of compact stars (also known as Type I). Even though most LGRBs are Type II and most SGRBs are Type I, the duration criterion is not always reliable to determine the physical category of a certain GRB. Based on our previous comprehensive study of the multiwavelength properties of long and short GRBs, here we utilize the naive Bayes method to physically classify GRBs as Type I and Type II GRBs based on multiwavelength criteria. It results in a 0.5% training error rate and a 1% test error rate. Moreover, there is a gap [−1.2, −0.16] in the distribution of the posterior odds, , the Type II to Type I probability ratio. Therefore, we propose to use as the parameter to classify GRBs into Type I (<0) or Type II (>0). The only confirmed Type I GRB, GRB 170817A, has log. According to this criterion, the supernova-less long GRBs 060614 and 060505 belong to Type I, and two controversial short GRBs 090426 and 060121 belong to Type II. [ABSTRACT FROM AUTHOR]

Shocks of supernova remnants (SNRs) are important (and perhaps the dominant) agents for the production of the Galactic cosmic rays. Recent γ-ray observations of several SNRs have made this case more compelling. However, these broadband high-energy measurements also reveal a variety of spectral shapes demanding more comprehensive modeling of emissions from SNRs. According to the locally observed fluxes of cosmic-ray protons and electrons, the electron-to-proton number ratio is known to be about 1%. Assuming such a ratio is universal for all SNRs and identical spectral shape for all kinds of accelerated particles, we propose a unified model that ascribes the distinct γ-ray spectra of different SNRs to variations of the medium density and the spectral difference between cosmic-ray electrons and protons observed from Earth to transport effects. For low-density environments, the γ-ray emission is inverse-Compton dominated. For high-density environments like systems of high-energy particles interacting with molecular clouds, the γ-ray emission is π0-decay dominated. The model predicts a hadronic origin of γ-ray emission from very old remnants interacting mostly with molecular clouds and a leptonic origin for intermediate-age remnants whose shocks propagate in a low-density environment created by their progenitors via, e.g., strong stellar winds. These results can be regarded as evidence in support of the SNR origin of Galactic cosmic rays. [ABSTRACT FROM AUTHOR]

From a practical point of view, a critical issue for the spin transfer effect is the reduction of the critical switching current density Jc. Over the past few years, the reported Jc at room temperature is in the range of 106 A cm−2. Here we report a low critical switching current density Jc of about 4.2 × 103 A cm−2 for spin transfer in Fe–MgO nanoscale granular film at room temperature, which is due to the low effective anisotropy field of the small Fe particles. [ABSTRACT FROM AUTHOR]

The discharge characteristics of capacitively coupled argon plasmas driven by very high frequency discharge are studied. The mean electron temperature and electron density are calculated by using the Ar spectral lines at different values of power (20 W–70 W) and four different frequencies (13.56 MHz, 40.68 MHz, 94.92 MHz, and 100 MHz). The mean electron temperature decreases with the increase of power at a fixed frequency. The mean electron temperature varies non-linearly with frequency increasing at constant power. At 40.68 MHz, the mean electron temperature is the largest. The electron density increases with the increase of power at a fixed frequency. In the cases of driving frequencies of 94.92 MHz and 100 MHz, the obtained electron temperatures are almost the same, so are the electron densities. Particle-in-cell/Monte-Carlo collision (PIC/MCC) method developed within the Vsim 8.0 simulation package is used to simulate the electron density, the potential distribution, and the electron energy probability function (EEPF) under the experimental condition. The sheath width increases with the power increasing. The EEPF of 13.56 MHz and 40.68 MHz are both bi-Maxwellian with a large population of low-energy electrons. The EEPF of 94.92 MHz and 100 MHz are almost the same and both are nearly Maxwellian. [ABSTRACT FROM AUTHOR]

We develop a new method based on Gaussian processes to reconstruct the mass distribution of binary black holes (BBHs). Instead of prespecifying the formalisms of mass distribution, we introduce a more flexible and nonparametric model with which the distribution can be mainly determined by the observed data. We first test our method with simulated data and find that it can well recover the injected distribution. Then, we apply this method to analyze the data of BBHs' observations from LIGO-Virgo Gravitational-Wave Transient Catalog 2. By reconstructing the chirp mass distribution, we find that there is a peak or a platform located at 20–30 M⊙ rather than a single-power-law-like decrease from low mass to high mass. Moreover, one or two peaks in the chirp mass range of may be favored by the data. Assuming a mass-independent mass ratio distribution of p(q) ∝ q1.4, we further obtain a distribution of primary mass and find that there is a feature located in the range of (30, 40) M⊙, which can be related to Broken Power Law and Power Law + Peak distributions described in Collaboration et al. Besides, the merger rate of BBHs is estimated to be , supposing that there is no redshift evolution. [ABSTRACT FROM AUTHOR]

A novel 3300 V high voltage carrier stored trench bipolar transistor (CSTBT) with common anode polysilicon diodes gate structure (CAPD-CSTBT) is proposed. The PN junctions and N+ emitter region in the polysilicon gate structure are beneficial for reducing the Miller capacitance by 88.1% and the input capacitance by 26.0%, while due to the polysilicon PN junction barrier, the forward and reverse gate bias voltage will not be affected. As a result, the transient energy loss could be decreased by 32.2% with the same range of Rg. Since the displacement current is shielded by the embedded emitter on the bottom of the CAPD gate structure, the (dICE/dt)max/ILoad is lower than that of the Fin-P-CSTBT by 81.8% on average with the same range of turn-on energy loss. Furthermore, the proposed structure features a 58.7% lower (dVKA/dt)max/Vcc value for the free-wheeling diode on average. By Fourier transformation, the proposed structure represents lower amplitudes for the ICE and VKA spectrums during the turn-on period, which is a drastic suppression of electromagnetic interference noise. [ABSTRACT FROM AUTHOR]

Radiative energy losses are very important in regulating the cosmic ray electron and/or positron (CRE) spectrum during their propagation in the Milky Way. Particularly, the Klein–Nishina (KN) effect of the inverse Compton scattering (ICS) results in less efficient energy losses of high-energy electrons, which is expected to leave imprints on the propagated electron spectrum. It has been proposed that the hardening of CRE spectra around 50 GeV observed by Fermi-LAT, AMS-02, and DAMPE could be due to the KN effect. We show in this work that the transition from the Thomson regime to the KN regime of the ICS is actually quite smooth compared with the approximate treatment adopted in some previous works. As a result, the observed spectral hardening of CREs cannot be explained by the KN effect. It means that an additional hardening of the primary electrons spectrum is needed. We also provide a parameterized form for the accurate calculation of the ICS energy-loss rate in a wide energy range. [ABSTRACT FROM AUTHOR]

In this report, the analytical expression of Coulombic interaction between a spherical nanoparticle and a tetragonal nanorod is derived. To evaluate the Coulombic interaction in the oriented attachment growth of tetragonal nanorods, we analyze the correlation between the Coulombic interaction and the important growth parameters, including: nanoparticle—nanorod separation, aspect ratio of the nanorods, and surface charge density. Our work opens up the opportunity to investigate interparticle interactions in the oriented attachment growth of tetragonal nanorods. [ABSTRACT FROM AUTHOR]