New radio (MeerKAT and Parkes) and X-ray (XMM-Newton, Swift, Chandra, and NuSTAR) observations of PSR J1622–4950 indicate that the magnetar, in a quiescent state since at least early 2015, reactivated between 2017 March 19 and April 5. The radio flux density, while variable, is approximately 100× larger than during its dormant state. The X-ray flux one month after reactivation was at least 800× larger than during quiescence, and has been decaying exponentially on a 111 ± 19 day timescale. This high-flux state, together with a radio-derived rotational ephemeris, enabled for the first time the detection of X-ray pulsations for this magnetar. At 5%, the 0.3–6 keV pulsed fraction is comparable to the smallest observed for magnetars. The overall pulsar geometry inferred from polarized radio emission appears to be broadly consistent with that determined 6–8 years earlier. However, rotating vector model fits suggest that we are now seeing radio emission from a different location in the magnetosphere than previously. This indicates a novel way in which radio emission from magnetars can differ from that of ordinary pulsars. The torque on the neutron star is varying rapidly and unsteadily, as is common for magnetars following outburst, having changed by a factor of 7 within six months of reactivation.
Polycrystalline gallium nitride films, 100 nm to 1 m thick, were deposited under a range of conditions. Substrate electrode temperatures during sputtering were varied from room temperature to 450°C, the pressure from 0.15 to 6.0 Pa, the nitrogen fraction of the deposition atmosphere from 10% to 100% and the target bias from −400 to − 1800 V. The deposition rates as functions of these conditions are in the range 0.5-25 nm/ min. The growth rate is considered to be controlled respectively by the thermally activated desorption from the substrate, changes in the mean free path and concentration of gas particles, differences between the sputter yields of Ga and GaN in Ar and N 2 , and changes in the ion current and sputter yields. The films are generally columnar, with the grain size increasing with film thickness. The most crystalline films were grown at mid range temperatures, low N 2 concentrations, and low target biases, and the most disordered were grown at low pressures. The latter two cases suggest that decreasing the energy of particles incident on the film during deposition results in a more ordered film. The biaxial stress is compressive and shows an increasing trend with the target bias and N 2 concentration, reaching 4.7 GPa at 75% N 2 . Oxygen contamination of 3 -30 at. % has a major effect on the optical properties of the films, increasing the band gap values from 3.02 to Ͼ 4.0 eV and the Urbach tail energies from around 150 to 840 meV and decreasing the refractive index from 2.46 to 2.03. At a 40% N 2 deposition fraction, the N:Ga ratio is more or less constant at 1:1. Since the absolute oxygen incorporation rate changes very little, it is the relative film deposition rate which determines the final oxygen concentration. Excess Ga at low N 2 concentrations causes a decrease in the band gap and an increase in the Urbach tail energy.
The room-temperature photoluminescence intensity and conductivity of GaN films grown by reactive rf sputtering were improved by the addition of hydrogen during growth. The differential resistivity decreased by two orders of magnitude when 2.4% H 2 was added to the deposition gas. The improvement in the photoluminescence intensity occurred together with an increase in the level of oxygen contamination and an apparent increase in the structural disorder. At 0 and 20% H 2 , respectively, the refractive indices were 2.45 and 1.98, and the bandgaps were 3.06 and 3.64 eV, with the change attributed to oxygenation.
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