Current sheet is a commonly observed structure involved in solar eruptions. However, the physical properties of its fine structures during a solar eruption are rarely investigated. Here, we report an on-disk observation that displays 139 compact, circular or elliptic bright structures, presumably plasma blobs, propagating bidirectionally along a plasma sheet during a period of about 24 minutes around the peak time of an eruptive flare. From extreme ultraviolet images, we distinguish a plasma sheet connecting the flare loops and the erupting filament. The average width, duration, and projected velocities of these blobs are about 1.7±0.5 Mm, 73±54 s, and 190±81 km/s, respectively. The reconnection site rises with an average velocity of about 51 km/s. We have obtained the temporal variation of the blob number during the solar eruption, which is similar to that of the GOES X-ray flux. The observational results suggest that plasmoid instability plays an important role in the energy release process of solar eruptions.

We report the observation of nonstationary quasi-periodic pulsations (QPPs) in high-energy particles during the impulsive phase of an X4.8 flare on 2002 July 23 (SOL2002-07-23T00:35). The X4.8 flare was simultaneously measured by the Reuven Ramaty High Energy Solar Spectroscopic Imager, Nobeyama Radio Polarimeters, and Nobeyama Radioheliograph. The quasi-period of ∼50 ± 15 s, determined by the wavelet transform, is detected in the γ -ray line emission. Using the same method, a quasi-period of ∼90 ± 20 s is found in the γ -ray continuum, hard X-ray (HXR), and radio emissions during almost the same time. Our observations suggest that the flare QPPs should be associated with energetic ions and nonthermal electrons that are quasi-periodically accelerated by the repetitive magnetic reconnection. The different quasi-periods between the γ -ray line and continuum/HXR/radio emissions indicate an apparent difference in acceleration or propagation between energetic ions and nonthermal electrons of this solar flare.

An analytical model of an RF phasing method using arbitrary phase scanning for bunch length measurement is reported. We set up a statistical model instead of a linear chirp approximation to analyze the energy modulation process. It is found that, assuming a short bunch (σφ∕2π→0) and small relative energy spread (σγ∕γr→0), the energy spread (Y=σγ2) at the exit of the traveling wave linac has a parabolic relationship with the cosine value of the injection phase (X=cosφr|z=0), i.e., Y=AX2+BX+C. Analogous to quadrupole strength scanning for emittance measurement, this phase scanning method can be used to obtain the bunch length by measuring the energy spread at different injection phases. The injection phases can be randomly chosen, which is significantly different from the commonly used zero-phasing method. Further, the systematic error of the reported method, such as the influence of the space charge effect, is analyzed. This technique will be especially useful at low energies when the beam quality is dramatically degraded and is hard to measure using the zero-phasing method.

A proton therapy facility with two 360° gantry treatment rooms and one fixed beamline is under development at the Huazhong University of Science and Technology (HUST), which is based on an isochronous superconducting cyclotron. The energy is modulated in the range of 70-240 MeV with an energy selection system. In this paper, we report the main design specifications of the beamline in the HUST-PTF project, in which the main features are the intensity suppression scheme beamline. Two prototype magnets (one quadrupole and one dipole) used in the beamline are also studied and presented. Two-dimensional contour optimization and pole-end chamfer iteration are used to minimize the harmonic errors of the integral field. Finally, both the field homogeneity and multipole errors achieve the precision requirement over the operating field range.

A proton therapy project HUST-PTF (HUST Proton Therapy Facility) based on a 250 MeV isochronous superconducting cyclotron is under development in Huazhong University of Science and Technology (HUST). In this paper we report the main design features of the beam line in HUST-PTF project. The energy selection system (ESS) for energy modulation is discussed in detail, including the collimators, momentum slit and transmission calculation. Due to significant difference among the transmissions of ESS for different energies, the intensity suppression scheme by defocusing beam at high energies on collimators in the beam line is proposed and discussed. Finally, the ratios of beam intensities between low and high energies are expected to be controlled within 10 to meet the clinical requirement, and the beam optics of each energy step after intensity suppression is studied respectively.

The relativistic external shock model of gamma-ray burst (GRB) afterglows has been established with five free parameters, i.e., the total kinetic energy E, the equipartition parameters for electrons is an element of(e) and for the magnetic field is an element of(B), the number density of the environment n and the index of the power-law distribution of shocked electrons p. A lot of modified models have been constructed to consider the variety of GRB afterglows, such as: the wind medium environment by letting n change with radius, the energy injection model by letting kinetic energy change with time and so on. In this paper, by assuming all four parameters (except p) change with time, we obtain a set of formulas for the dynamics and radiation, which can be used as a reference for modeling GRB afterglows. Some interesting results are obtained. For example, in some spectral segments, the radiated flux density does not depend on the number density or the profile of the environment. As an application, through modeling the afterglow of GRB 060607A, we find that it can be interpreted in the framework of the time dependent parameter model within a reasonable range.

A proton therapy facility with two 360° gantry treatment rooms and one fixed beamline is under development in the Huazhong University of Science and Technology, which is based on the isochronous superconducting cyclotron scheme. This paper presents the beam optics and main magnetic elements including dipoles, quadrupoles, and fast scanning magnets of the gantry beamline. In addition, the energy selection system will be introduced, which enables fast energy modulation of proton beam between 70 and 240 MeV.

Mergers of neutron star–neutron star (NS–NS) or neutron star–black hole (NS–BH) binaries are candidate sources of gravitational waves (GWs). At least a fraction of the merger remnants should be a stellar mass BH with sub-relativistic ejecta. A collimated jet is launched via the Blandford–Znajek mechanism from the central BH to trigger a short gamma-ray burst (sGRB). At the same time, a near-isotropic wind may be driven by the Blandford–Payne mechanism (BP). In previous work, additional energy injection to the ejecta from the BP mechanism was ignored, and radioactive decay has long been thought to be the main source of the kilonova energy. In this Letter, we propose that the wind driven by the BP mechanism from the newborn BH’s disk can heat up and push the ejecta during the prompt emission phase or even at late times when there is fall-back accretion. Such a BP-powered merger-nova could be bright in the optical band even for a low-luminosity sGRB. The detection of a GW merger event with a BH clearly identified as a remnant, accompanied by a bright merger-nova, would provide robust confirmation of our model.

A new proton therapy facility (HUST-PTF) is under construction in the Huazhong University of Science and Technology. The integral field measurement system of dipole magnets was designed for the beamline of HUST-PTF. The design goal is to build a reliable, precise, and automatic measurement system, which is accurate enough to characterize the magnetic field quality of the dipole magnets. The system consists of long coils, precision motion stages, data acquisition, and control system. The design of the whole system and the measurement method is described in this paper. The design and fabrication of the long coil are also discussed, and the errors from the geometric frame of coil and electronic equipment are analyzed.

A proton therapy facility based on an isochronous superconducting cyclotron is under construction in Huazhong University of Science and Technology (HUST). To meet the clinical requirements, an energy degrader is essential in the beamline to modulate the fixed beam energy extracted from the cyclotron. Because of the multiple Coulomb scattering in the degrader, the beam emittance and the energy spread will be considerably increased during the energy degradation process. Therefore, a set of collimators is designed to restrict the increase in beam emittance after the energy degradation. The energy spread will be reduced in the following beam line which is not discussed in this paper. In this paper, the design considerations of an energy degrader and collimators are introduced, and the properties of the degrader material, degrader structure and the initial beam parameters are discussed using the Geant4 Monte-Carlo toolkit, with the main purpose of improving the overall performance of the degrader by multiple parameter optimization.

The weak short gamma-ray burst (GRB) 170817A was accompanied by the GW170817 gravitational-wave event and is believed to have been produced by an off-beam relativistic jet. Here, we use the E-p,E- i-E-iso and Gamma-E-iso relations to determine its Lorentz factor Gamma and the viewing angle from the edge of the jet theta'(obs) of GRB 170817A. Our results indicate that Gamma = 13.4-(5.5) (+9.8) and theta'(obs) =4 degrees 3(-1.5)(+1.8), corresponding to an on-axis E-p,E-i = 415(-1.67)(+361) keV and E-iso = (2.4(-1.9)(+1.6)) 10(47) erg. Therefore, the GRB was an intrinsically weak short GRB. We also find that the afterglow emission was in good agreement with the follow-up multiband observations and that the radio emissions at around 20 days may have come from the off-axis jet. Interestingly, the Doppler factor and luminosity follow a universal relation for GRBs and blazars, thus suggesting that they may share a similar radiation mechanism.

An X-ray plateau followed by a steep decay (" internal plateau") has been observed in both long and short gammaray burst (GRBs), implying that a millisecond magnetar operates in some GRBs. The sharp decay at the end of the plateau, marking the abrupt cessation of the magnetar's central engine, has been considered the collapse of a supramassive magnetar into a black hole (BH) when it spins down. If this " internal plateau" is indeed evidence of a magnetar central engine, the natural expectation in some candidates would be a signature from the newborn BH. In this work, we find that GRB 070110 is a particular case which shows a small X-ray bump following its " internal plateau." We interpret the plateau as a spin-down supra-massive magnetar and the X-ray bump as fallback BH accretion. This indicates that a newborn BH is likely active in some GRBs. Therefore, GRB 070110-like events may provide further support to the magnetar central engine model and enable us to investigate the properties of the magnetar as well as the newborn BH.

Proton therapy is now recognized as one of the most effective radiation therapy methods for cancers. A proton therapy facility with multiple gantry treatment rooms is under development in HUST (Huazhong University of Science and Technology), which is based on isochronous superconducting cyclotron scheme. In the beam line, the scanning system spreads out the proton beam on the target according to the complex tumour shape by two scanning magnets for horizontal and vertical scanning independently. Since these two magnets are excited by alternating currents and the maximum repetition frequency is up to 100Hz, eddy currents and losses are expected to be significant. Slits are proven to be an effective way to reduce the eddy currents. To evaluate the heat distribution due to eddy losses in the pole end of the scanning magnet, the transient electromagnetic analysis and steady-state thermal analysis are performed. This paper describes design considerations of the scanning system and mainly analyses the eddy current effect of the scanning magnets. Different coil shapes and slit arrangements are simulated and compared to obtain the optimal configuration. The maximum temperatures of two magnets are optimized below 70°C. In addition, the lag effect due to eddy currents is also discussed.

GRB 131231A was detected by the Large Area Telescope on board the Fermi Space Gamma-ray Telescope. The high-energy gamma-ray (>100 MeV) afterglow emission spectrum is F-nu proportional to nu(-0.54 +/- 0.15) in the first similar to 1300 s after the trigger and the most energetic photon has an energy of similar to 62 GeV, arriving at t similar to 520 s. With reasonable parameters of the gamma-ray burst (GRB) outflow as well as the density of the circum-burst medium, the synchrotron radiation of electrons or protons accelerated at an external forward shock have difficulty accounting for the data. Rather, the synchrotron self-Compton radiation of the forward shock-accelerated electrons can account for both the spectrum and temporal behavior of the GeV afterglow emission. We also show that the prospect for detecting GRB 131231A-like GRBs with the Cherenkov Telescope Array is promising.

The high-mass X-ray binary 4U 1901+03 is reported to have a pulse profile evolving with the X-ray luminosity and energy during its outburst in 2003 February–July: the pulse peak changed from double to single along with the decreasing luminosity. We have carried out a detailed analysis on the contemporary phase-resolved energy spectrum of 4U 1901+03 as observed by the Rossi X-ray Timing Explorer. We find that the spectra are phase dependent. At the beginning of the outburst, the maximum of the optical depth for Compton scattering is near the major phase peak. During the decay of the outburst, the optical depth has the maximum away from the main peak of the pulse profile. For each observation, Fe Kα emission line is detected in the phase-resolved spectra, and its flux is constant across the pulse phases. This suggests that the origin of the Fe emission is from the accretion disk, not the surface of the neutron star.

After a silence of some 32 years, the high-mass X-ray binary (HMXB) 4U1901+03 produced an outburst in Feb. 2003. With the observed data of RXTE (Rossi X-ray Timing Explorer) over a 5 month duration, we have made a systematic study of the pulse profile of this source, and obtained its time evolution and its correlation with the photon energy. It is found that the variations of the pulse profile and the pulse fraction with the accretion rate of the binary system exhibit a stepwise evolution, and that the pulse fraction reaches its peak at energies under ten KeV. The complex variation of the pulse profile indicates that the pulse profile can not be explained by a single geometrical or physical model, rather, it must be related with both the viewing angle and the radiation mechanism. The observed features are here discussed in terms of the standard radiation model of pulsars.