High-energy Peak Research Articles

GRB 210121A: A Typical Fireball Burst Detected by Two Small Missions

Abstract The Chinese CubeSat Mission, Gamma Ray Integrated Detectors (GRID), recently detected its first gamma-ray burst, GRB 210121A, which was jointly observed by the Gravitational wave high-energy Electromagnetic Counterpart All-sky Monitor (GECAM). This burst is confirmed by several other missions, including Fermi and Insight-HXMT. We combined multimission observational data and performed a comprehensive analysis of the burst’s temporal and spectral properties. Our results show that the burst is relatively special in its high peak energy, thermal-like low-energy indices, and large fluence. By putting it to the E p –E γ,iso relation diagram with assumed distance, we found that this burst can be constrained at the redshift range of [0.3, 3.0]. The thermal spectral component is also confirmed by the direct fit of the physical models to the observed spectra. Interestingly, the physical photosphere model also constrained a redshift of z ∼ 0.3 for this burst, which helps us to identify a host galaxy candidate at such a distance within the location error box. Assuming that the host galaxy is real, we found that the burst can be best explained by the photosphere emission of a typical fireball with an initial radius of r 0 ∼ 3.2 × 107 cm.

Observations of surface wave fields in the Arabian Sea under tropical cyclone Tauktae

The characteristics of surface wave fields in the eastern Arabian Sea under tropical cyclone Tauktae were investigated using buoy data. On May 16, 2021, the cyclone passed within 96 km of the buoy location, and a maximum wave height of 9.7 m with a significant wave height of 5.6 m was recorded by the buoy, moored at 23.5 m water depth off Goa. As the cyclone approached the buoy location, a shift in the frequency caused waves to turn into unimodal spectra with high wave energy and spectral peak parameter. Further, the evolution of cyclone-induced waves and their spatial variation have been investigated using the ERA5 reanalysis data. The results suggest that for distances of ∼400 km spatial extend from the cyclone's eyewall, the cyclone induced waves to have a high impact with significant wave height above 3 m for a cyclone sustained wind speed of around 100–120 knots. The dominance of wind-seas over swells and the directional shift are noticeable, specifically along the west coast of India during the tropical cyclone passage.

Efficient high-energy photon production in the supercritical QED regime

When dense high-energy lepton bunches collide, the beam particles can experience rest-frame electromagnetic fields which greatly exceed the QED critical one. Here it is demonstrated that beamstrahlung efficiently converts lepton energy to high-energy photons in this so-called supercritical QED regime, as the single-photon emission spectrum exhibits a pronounced peak close to the initial lepton energy. It is also shown that the observation of this high-energy peak in the photon spectrum requires one to mitigate multiple photon emissions during the interaction. Otherwise, the photon recoil induces strong correlations between subsequent emissions which soften the photon spectrum and suppress the peak. The high-energy peak in the photon spectrum constitutes a unique observable of photon emission in the supercritical QED regime and provides decisive advantages for the realization of an efficient multi-TeV laserless gamma-gamma collider based on electron-electron collisions.

Spectral-luminescence properties of freestanding porous SiC layers

We report about structural and photoluminescence properties of porous silicon carbide formed by electrochemical etching of SiC plate. The existence of a crystallite size gradient is shown across the layer. The spectrum of the photoluminescence is observed in the visible region and can be fitted at least by three peaks. The obtained photoluminescent properties are discussed with the results of the SEM, TEM and Raman studies. The nature of the low-energy peak is explained by electron-hole recombination at some localized states; the middle energy peak is related to the surface defect centers introduced by the HF reaction on the Si surface (CFO), the high energy peak can be explained by SiC nanocrystallites.

Exploration of the nonideal behavior observed in engineered, multilayer MgO/Ag/MgO photocathodes

Improving photocathode performance by increasing electron emission while lowering the angular spread of emitted electrons can improve particle accelerator performance, expanding the reach of both fundamental and applied science. Materials science expertise is needed to design new photocathodes with these desired properties. In this work, we have undertaken a study of the electronic structure of the interfaces in a multilayer photocathode structure consisting of MgO/Ag/MgO to explore how the fabrication process can lead to nonideal interfaces compared to those constructed in simulations. To study how the fabrication affects the interfaces, hard x-ray photoemission spectroscopy was used to probe the chemistry of the buried interfaces within the thin film multilayer structure of Ag and MgO. In these multilayer structures, we observed that the silver layers were predominantly metallic. A small high binding energy (ΔE=0.69 eV) peak was also observed in the Ag 3d core level in the samples. This peak is shifted in the opposite direction of the binding energy shift in silver oxides, suggesting that this peak is not due to formation of silver oxides at the interfaces with the MgO. Two possible explanations for the origin of this peak then are charge transfer at the interface from the Ag to the oxide monolayer or the formation of silver nanoparticles during the growth process. Based upon simple depth profiling analysis, we postulate that the former is the more likely explanation but cannot rule out the latter. In addition, the O 1s and Mg 1s core level indicated the presence of Mg(OH)2. The MgO layers react with H2O in the vacuum chamber or ideal gas used as a buffer during sample transfer. Since the theory predicts strong dependence upon the number of MgO layers surrounding the Ag, the formation of Mg(OH)2 likely contributes to the nonideal behavior, even given the similarity in the electronic structure to MgO (large bandgap insulator) and Mg(OH)2. The speed at which this reaction occurs would significantly limit the lifetime and the utility of the MgO/Ag multilayer photocathodes. In order to custom engineer multilayer photocathodes, complete control over the growth process will be needed to ensure that the ideal surfaces are formed. Using nonreactive materials would greatly increase the lifetime of the engineered photocathodes.

Properties of secondary ions in ion beam sputtering of Ga2O3

The energy distributions of secondary ions for the ion beam sputtering of a Ga2O3 target using O2+ and Ar+ ions are measured in dependence on various process parameters using energy-selective mass spectrometry. The process parameters include sputtering geometry (ion incidence angle α, polar emission angle β, scattering angle γ), the energy of incident ions Eion, and the background pressure of O2. The main secondary ion species are identified to be Ga+, O+, O2+, and, when argon is used as a process gas, Ar+. The changes in the sputtering geometry and the primary ion energy have the most impact on the energy distributions of secondary Ga+ and O+ ions, giving control over the high-energy tail, which is attributed to anisotropy effects in sputtering. The formation of O2+ ions is attributed to collisions with background gas molecules, as their energy distributions are not influenced by the sputtering geometry or the primary ion energy. The increase of the O2 pressure leads to a minor decrease of the energy of Ga+ ions due to collisions with the background gas particles. The use of primary Ar+ ions with O2 background pressure does not show any specific effect on energy distributions of Ga+, O+, and O2+ ions except for the case without additional O2 background. In the latter case, much fewer O+ and O2+ ions are produced indicative of oxygen depletion of the surface due to preferential sputtering of oxygen. At all considered O2 pressures, the energy distributions of Ar+ ions have a high-energy peak, attributed to direct scattering events. The trends in experimental data show qualitative agreement to simulations using the Monte Carlo code SDTrimSP.

Effect of surface morphology on macroscale and microscale optical properties of layered InSe grown by molecular beam epitaxy

This paper reports the results on the microphotoluminescence (µPL) and photoreflectance (PR) spectroscopy studies of InSe thin film grown by molecular beam epitaxy on GaAs(001) substrate. The specific surface morphology of the InSe/GaAs(001) layer consisting of a number of randomly oriented nanoplatelets with the average thickness of 40–200 nm leads to a difference in optical properties measured on the macroscale (PR) and microscale (µPL). The highest energy peak at 1.348 eV observed in the µPL spectra at low excitation densities was attributed to the recombination of localized excitons in ε -InSe.

Hydrogen-Bonding-Induced H-Aggregation of Charge-Transfer Complexes for Ultra-Efficient Second Near-Infrared Region Photothermal Conversion

Hydrogen-Bonding-Induced H-Aggregation of Charge-Transfer Complexes for Ultra-Efficient Second Near-Infrared Region Photothermal Conversion

Numerical investigation of a radio frequency sheath with supra-thermal electrons in the presence of the magnetic field

The structure of the magnetized radio-frequency (RF) sheath of plasma containing supra-thermal electrons is studied numerically with a one-dimensional hybrid model consisting of a collisionless sheath model and an equivalent circuit model of the sheath. It is found that effect of the external magnetic field on the sheath structure depends on the direction of the disturbance current source. As the plasma magnetization or angle between the magnetic field and the wall is increased, both the sheath thickness and sheath potential drop increase during the positive disturbance current source at the wall, while they change slightly during the negative disturbance current source at the wall. For the different supra-thermal electron populations parameterized by Kappa velocity distribution, both the sheath thickness and sheath potential drop are always larger in the magnetized sheath than in the unmagnetized sheath. Compared with in the unmagnetized sheath, the width of the ion energy distribution (IED) in the magnetized sheath expands towards the high energy regime, and the low-energy peak of the IED decreases while the high-energy peak of the IED changes a little.

Ion energy distribution functions in a dual-frequency low-pressure capacitively-coupled plasma: experiments and particle-in-cell simulation

Low-pressure (<10 s mTorr) multi-frequency capacitively coupled plasmas (CCPs) are essential for critical plasma processing applications such as high aspect ratio dielectric etching for 3D memory fabrication. As the processing requirements become more stringent for future microelectronics technologies, plasma simulations are being used to help design industrial CCPs with the goal of accurately controlling the ion energy and ratio of ion to radical flux. Experimental validation is critical for developing trust-worthy plasma models. In this paper, a 1D particle-in-cell (PIC) model is used to simulate the ion kinetics and sheath dynamics in low pressure (a few to 10 s mTorr) dual-frequency (100 s kHz to 10 s MHz) Ar CCPs. Experimental results are compared to the 1D PIC model over a range of conditions. With pressure as low as 2 mTorr, a double-peak IEDF is predicted by the model; as the pressure increases to 20 mTorr, the double-peak IEDFs gradually shift to an IEDF with a strongly depleted high energy tail due to the higher ion-neutral collision frequency. The high energy peak of the bimodal IEDFs shifts to higher energy with increasing low-frequency voltage while the low energy peaks remain unmoved. When the low-frequency increases, the width of the IEDFs reduces, and new peaks at low energy emerge. The IEDFs from the PIC modeling results agree well with measurements.

Magnetic polaron-related optical properties in Ni(II)-doped CdS nanobelts: Implication for spin nanophotonic devices

Emissions by magnetic polarons and spin-coupled d–d transitions in diluted magnetic semiconductors (DMSs) have become a popular research field due to their unusual optical behaviors. In this work, high-quality NiI2(II)-doped CdS nanobelts are synthesized via chemical vapor deposition (CVD), and then characterized by scanning electron microscopy (SEM), x-ray diffraction, x-ray photoelectron spectroscopy (XPS), and Raman scattering. At low temperatures, the photoluminescence (PL) spectra of the Ni-doped nanobelts demonstrate three peaks near the band edge: the free exciton (FX) peak, the exciton magnetic polaron (EMP) peak out of ferromagnetically coupled spins coupled with FXs, and a small higher-energy peak from the interaction of antiferromagnetic coupled Ni pairs and FXs, called antiferromagnetic magnetic polarons (AMPs). With a higher Ni doping concentration, in addition to the d–d transitions of single Ni ions at 620 nm and 760 nm, two other PL peaks appear at 530 nm and 685 nm, attributed to another EMP emission and the d–d transitions of the antiferromagnetic coupled Ni2+–Ni2+ pair, respectively. Furthermore, single-mode lasing at the first EMP is excited by a femtosecond laser pulse, proving a coherent bosonic lasing of the EMP condensate out of complicated states. These results show that the coupled spins play an important role in forming magnetic polaron and implementing related optical responses.

Structures of (NaSCN)2(H2O)n -/0 (n = 0-7) and solvation induced ion pair separation: Gas phase anion photoelectron spectroscopy and theoretical calculations.

We studied (NaSCN)2(H2O)n - clusters in the gas phase using size-selected anion photoelectron spectroscopy. The photoelectron spectra and vertical detachment energies of (NaSCN)2(H2O)n - (n = 0-5) were obtained in the experiment. The structures of (NaSCN)2(H2O)n -/0 up to n = 7 were investigated with density functional theory calculations. Two series of peaks are observed in the spectra, indicating that two types of structures coexist, the high electron binding energy peaks correspond to the chain style structures, and the low electron binding energy peaks correspond to the Na-N-Na-N rhombic structures or their derivatives. For the (NaSCN)2(H2O)n - clusters at n = 3-5, the Na-N-Na-N rhombic structures are the dominant structures, the rhombic four-membered rings start to open at n = 4, and the solvent separated ion pair (SSIP) type of structures start to appear at n = 6. For the neutral (NaSCN)2(H2O)n clusters, the Na-N-Na-N rhombic isomers become the dominant starting at n = 3, and the SSIP type of structures start to appear at n = 5 and become dominant at n = 6. The structural evolution of (NaSCN)2(H2O)n -/0 (n = 0-7) confirms the possible existence of ionic clusters such as Na(SCN)2 - and Na2(SCN)+ in NaSCN aqueous solutions.

Improvement of electron beam quality in laser wakefield acceleration by a circularly-polarized laser pulse

Electron acceleration driven by laser wakefield using a laser pulse with circular polarization is studied to generate better-quality electron bunches. In order to inject electrons into the accelerating phase of the plasma wave, a density transition shaped bump is employed. Using particle-in-cell simulations, we demonstrate the influence of laser polarization on the quality of electron bunch. The simulation results (using experimentally achievable parameters) show that the electron bunch with higher peak-energy, narrow energy-spread, and low emittance can be obtained by using a laser pulse with circular polarization as compared to the usually employed linear polarization in a mm-scale length plasma. The results show the improved quality of the electron bunch generated from laser wakefield accelerations. The predicted electron bunch quality may be crucial in developing plasma-based electromagnetic radiation sources.

Combustion of Flat Shaped Char Particles With Oxygen

Abstract Thin flat-shaped carbon black particles of 1.5 mm thickness by 22.5 mm diameter were combusted in pure oxygen at atmospheric pressures and temperatures in the range of 500–650 °C. One-film kinetic-diffusion model was derived to characterize the kinetic and energy parameters for particles arranged in the form of a thin flat-shaped configuration. The kinetic and energy parameters, and operating regimes of thin flat-shaped char particles were characterized during the nonisothermal combustion process. The gasification regimes during preheating were also analyzed. Steady-state energy processes were considered to derive an energy conservation equation used for calculating the evolution of char surface temperatures as well as released peak energy rates and the specific energy, which are considered key engineering design parameters. The one-film kinetic-diffusion model showed that combustion of such particles was purely kinetic controlled under these conditions. The activation energy obtained varied between 50 and 74 kJ/mol using discrete time and linear fits to the Arrhenius equation. The total energies released per weight of char converted varied between 32.8 and 40.6 kJ/g. The highest peak energy rate released was 134 J/s when combusting char in O2 at a reactor temperature of 504 °C.

Hybrid simulation of radio frequency biased inductively coupled Cl2 plasmas

In the etching process, a bias source is usually applied to the bottom electrode of an inductively coupled plasma (ICP) source to control the ion energy and angular distribution function (IEADF) independently. In this work, a hybrid model, i.e., a global model combined bi-directionally with a fluid sheath model, is applied to investigate the plasma properties in biased ICPs sustained in Cl2 gases. The evolutions of the plasma properties with bias voltage are presented for various ICP powers (i.e., 200, 500, and 1000 W) at a pressure of 10 mTorr and bias frequency of 13.56 MHz. The results indicate that the Cl2 (v = 0) density decreases with ICP power, whereas the densities of electrons and Cl+ ions increase strikingly and they become the dominant charged species at 1000 W. In addition, the electron density and Cl+ density increase with bias voltage, and the increasing trend becomes more obvious at higher ICP powers. However, the evolution of the Cl2+ density and Cl− density with bias voltage depends on the ICP power. For instance, they first exhibit an increasing trend and then keep constant at 200 W, while a slight downward trend is observed at 1000 W. In addition, as the bias voltage increases, both the high-energy peak and low-energy peak of IEADFs move toward higher energy, and meanwhile the peak separation becomes wider. The results obtained in this work are of significant importance for improving the etching process.

Deciphering the Intense Postgap Absorptions of Monolayer Transition Metal Dichalcogenides.

Rich valleytronics and diverse defect-induced or interlayer pre-bandgap excitonics have been extensively studied in transition metal dichalcogenides (TMDCs), a system with fascinating optical physics. However, more intense high-energy absorption peaks (∼3 eV) above the bandgaps used to be long ignored and their underlying physical origin remains to be unveiled. Here, we employ momentum resolved electron energy loss spectroscopy to measure the dispersive behaviors of the valley excitons and intense higher-energy peaks at finite momenta. Combined with accurate Bethe-Salpeter equation calculations, non-band-nesting transitions at the Q valley and at the midpoint of KM are found to be responsible for the high-energy broad absorption peaks in tungsten dichalcogenides and present spin polarizations similar to A excitons, in contrast with the band-nesting mechanism in molybdenum dichalcogenides. Our experiment-theory joint research will offer insights into the physical origins and manipulation of the intense high-energy excitons in TMDC-based optoelectronic devices.

GRB 130310A: very high peak energy and thermal emission

The special GRB 130310A was observed by Fermi Gamma-Ray Burst Monitor and Large Area Telescope, with T 90∼ 2.4 s. With a combination of a Band function and a blackbody (BB) function, the time-resolved spectral analysis of GRB 130310A confirmed that there is a sub-dominate thermal component in the early period (e.g., slice T 0 + [4.03 – 4.14] s) spectrum with BB temperature (kT) being ∼7∼5 keV, which can be interpreted as photosphere emission. The precursor of GRB 130310A can be fitted well with a BB component with kT ∼ 45 keV, which is higher than that of the main burst. It suggests that the radiation of GRB 130310A is in transition from thermal to non-thermal. Such a transition is an indication of the change in jet composition from a fireball to a Poynting-flux-dominated jet. A very high peak energy is obtained in the first time bin, with the peak energy Ep of the Band component for Band+BB and Band model being ∼8.5∼5.2 MeV and ∼11.1∼7.4 MeV, respectively. Afterwards, the Ep drops to ∼ 1 MeV. The Ep evolution patterns with respect to the pulses in the GRB 130310A light curves show a hard-to-soft evolution. The interpretation of the high peak energy Ep within the photosphere and internal shock model is difficult. It also suggests that at least for some bursts, the Band component must invoke a non-thermal origin in the optically thin region of a GRB outflow. Assuming the redshift is z ∼ 0.1 ∼ 8, the radius of the jet base r 0 ∼ 109 cm to allow (1 + σ 15) > 1 in line with the calculation results of the magnetization parameter at ∼1015 cm (σ 15). However, the value of (1 + σ 15) is ≃ 1 in the zone z around 3 for r 0 ∼ 109 cm, suggesting the non-excluded possibility that the origin is from ICMART with a low value. The photosphere-internal shock seems capable of interpreting the high peak energy, which requires electron Lorentz factor γe ∼ 60 and εe ∼ 0.06.

GRB 191016A: A Long Gamma-Ray Burst Detected by TESS

Abstract The Transiting Exoplanet Survey Satellite (TESS) exoplanet-hunting mission detected the rising and decaying optical afterglow of GRB 191016A, a long gamma-ray burst (GRB) detected by Swift-BAT but without prompt XRT or UVOT follow-up due to proximity to the Moon. The afterglow has a late peak at least 1000 s after the BAT trigger, with a brightest-detected TESS data point at 2589.7 s post-trigger. The burst was not detected by Fermi-LAT, but was detected by Fermi-GBM without triggering, possibly due to the gradual nature of the rising light curve. Using ground-based photometry, we estimate a photometric redshift of z phot = 3.29 ± 0.40. Combined with the high-energy emission and optical peak time derived from TESS, estimates of the bulk Lorentz factor ΓBL range from 90 to 133. The burst is relatively bright, with a peak optical magnitude in ground-based follow-up of R = 15.1 mag. Using published distributions of GRB afterglows and considering the TESS sensitivity and sampling, we estimate that TESS is likely to detect ∼1 GRB afterglow per year above its magnitude limit.

Intrinsic and extrinsic bands in optical spectra of linear-chained carbon films on sodium and potassium chloride substrates

A practically important task of synthesizing isolated carbon nanostructures can be solved by removing soluble chloride substrates. However, a reliable express characterization method to control the synthesis results is needed. In this paper, the optical reflection and absorption spectra of the linear-chain carbon (LCC) films on sodium and potassium chlorides surfaces were studied numerically using DFT modeling. In the optical absorption and reflection spectra three peaks were found that are absent in the spectra of pure substrates. Two of them observed in red and UV regions of the difference absorption spectra have been mapped to transitions between carbon states seen in the electronic DOS. Chlorine and potassium/sodium energy states have been found to contribute to the high-energy VUV peak. The bands discovered would be useful for the rapid characterization of an LCC coating and determination of the crystalline substrate orientation.

Catalysis of core-shell nanoparticle M@Pt (M[dbnd]Co and Ni) for oxygen reduction reaction and its electronic structure in comparison to Pt nanoparticle

Oxygen reduction reaction (ORR) by Pt55 and core-shell M13@Pt42 (MCo or Ni) particles is explored theoretically. Rate-determining step (RDS) is the second OH formation in M13@Pt42 but the second H2O formation in Pt55. Activation energy of RDS decreases following the order Pt55 > Co13@Pt42 > Ni13@Pt42 and onset potential is larger in M13@Pt42 than in Pt55, showing M13@Pt42 is more active than Pt55. Lower energy d-valence band-top (φVB-top) of M13@Pt42 results in the higher activity of M13@Pt42 than that of Pt55, where φVB-top is the highest energy peak in d-valence band DOS. Thus, the φVB-top energy is important for ORR activity. The lower energy φVB-top of M13@Pt42 than that of Pt55 mainly arises from smaller exchange repulsion of Pt42 shell with M13 core than that with Pt13 core; smaller atomic size and d orbital size of Co and Ni than those of Pt are key factors.