Results 1 - 10 of 2315
Results 1 - 10 of 2315. Search took: 0.026 seconds
|Sort by: date | relevance|
[en] A modified technique of the self-absorption method has been developed and applied to natural mercury afterglows. A narrow light-emitting layer is produced inside an absorption tube by external pumping at the moment of measuring the afterglow. (orig.)
[en] Highlights: • Long afterglow of Zn3Al2Ge2O10:Cr3+ was caused by introducing Ca2+. • Bluish white emission of Zn3Al2Ge2O10:Cr3+ was created by introducing Ca2+. • Zn3Al2Ge2O10:Cr3+ can produce red emission in the range of 650–750 nm. The long afterglow and bluish white emission of red emitting material Zn3Al2Ge2O10:Cr3+ are induced by introducing Ca2+. Under excitation of 400 nm, Zn3Al2Ge2O10:Cr3+ can emit a red emission band at 694 nm in the range of 650–750 nm that is caused by 2E → 4A2 transition of Cr3+. Under 262 nm excitation, Zn3Al2Ge2O10:Cr3+ can produce a weakly broad emission band in the range of 350–600 nm, and the emission intensity of Zn3Al2Ge2O10:Cr3+ can be enhanced by tuning the ratio of Ca2+ to Zn2+, especially, Zn3Al2Ge2O10:Cr3+ can present a bluish white emission and long afterglow properties by introducing Ca2+. The bluish white luminescence is caused by increasing the intrinsic defects (VʺZn, VʺCa and VʺO). And Ca vacancies can assist to stabilize the O vacancies; therefore, Zn3Al2Ge2O10:Cr3+ show the long afterglow characteristics. It enriched the luminescent properties of Zn3Al2Ge2O10:Cr3+ by introducing Ca2+, since Zn3Al2Ge2O10:Cr3+ shows different characteristics under different radiation excitation.
[en] The electron energy distribution of an afterglow plasma is not a Maxwellian one but follows a more complex non-monotonic function. The mechanism leading to this distribution is analyzed in detail. The main effect is obtained by the noncontinuous, stepwise excitation process. The proposed theory explains the observed characteristics. The presence of ionized nonequilibrium distributions is discussed. The effect analyzed may play an important role in the afterglow of inert gases plasma. (D.Gy.)
[en] The new and extreme population of gamma-ray bursts (GRBs) detected by the Fermi Large Area Telescope (LAT) shows several new features in high-energy gamma rays that are providing interesting and unexpected clues into GRB prompt and afterglow emission mechanisms. Over the last six years, it has been Swift that has provided the robust data set of UV/optical and X-ray afterglow observations that opened many windows into components of GRB emission structure. The relationship between the LAT-detected GRBs and the well-studied, fainter, and less energetic GRBs detected by the Swift Burst Alert Telescope is only beginning to be explored by multi-wavelength studies. We explore the large sample of GRBs detected by BAT only, BAT and the Fermi Gamma-ray Burst Monitor (GBM), and GBM and LAT, focusing on these samples separately in order to search for statistically significant differences between the populations, using only those GRBs with measured redshifts in order to physically characterize these objects. We disentangle which differences are instrumental selection effects versus intrinsic properties in order to better understand the nature of the special characteristics of the LAT bursts.
[en] In this work, high temperature solid phase method was applied to prepare Sr2MgSi2O7:Eu, Dy blue light long-persistence materials with different contents of H3BO3. Under the condition of low H3BO3 content, it was difficult for Eu and Dy to enter Sr2MgSi2O7 lattice, impurity phase of Sr3MgSi2O8 was observed, and initial afterglow luminance of the sample was very low. With the increase of H3BO3, Sr3MgSi2O8 phase disappeared, Eu and Dy entered Sr2MgSi2O7 lattice smoothly, and the grain size as well as initial afterglow luminance of samples increased significantly. The initial afterglow luminance of the sample reached the maximum while the H3BO3 content was 10% (molar ratio). As H3BO3 content increased further, the initial afterglow luminance reduced rapidly. After detailed analysis, we consider that the key factors influencing the afterglow luminance of samples are the formation and the density of luminous unit, which is greatly determined by the Eu and Dy’s entering Sr2MgSi2O7 lattice as well as the grain size of Sr2MgSi2O7 crystal. (paper)
[en] A kinetic model is developed to study the afterglow plasma of a pulsed discharge in air. This model includes a detailed analysis of the temporal evolution of heavy species during the pulse, followed by their relaxation in the afterglow. The predicted results are compared with two experimental sets performed in the time afterglow of a pulsed discharge in N2-20%O2 at a pressure p = 133 Pa involving the measurements of (i) N2(B) and N2(C) fluorescences for a discharge current I = 40 mA and a pulse duration τ = 200 μs and 10 ms, together with (ii) the absolute concentration of NO(X) for I = 40 and 80 mA with τ varying from 1 to 4 ms. The results of the model agree reasonably well with the measurements of N2(B) and N2(C) decays. It is shown that under these experimental conditions, N2(B) is always populated mainly via the process N2(A) + N2(X, 5 ≤ v ≤ 14) → N2(B) + N2(X, v = 0), while the relaxation of N2(C) is dominated by the pooling reaction N2(A) + N2(A) → N2(C) + N2(X, v = 0). An almost constant concentration of NO(X) is experimentally observed until the remote afterglow, but the present model is only capable of predicting the same order of magnitude for afterglow times t ∼< 0.05 s. Several hypotheses are discussed and advanced in order to explain this discrepancy.
[en] We present the discovery of the optical afterglow and early-type host galaxy of the short-duration GRB 100117A. The faint afterglow is detected 8.3 hr after the burst with rAB = 25.46 ± 0.20 mag. Follow-up optical and near-infrared observations uncover a coincident compact red galaxy, identified as an early-type galaxy at a spectroscopic redshift of z ∼ 0.915 with a mass of ∼3 x 1010 Msun, an age of ∼1 Gyr, and a luminosity of LB ≅ 0.5 L*. From a possible weak detection of [O II]λ3727 emission at z = 0.915 we infer an upper bound on the star formation rate of ∼0.1 Msun yr-1, leading to a specific star formation rate of ∼<0.004 Gyr-1. Thus, GRB 100117A is only the second short burst to date with a secure early-type host (the other being GRB 050724 at z = 0.257) and it has one of the highest short gamma-ray burst (GRB) redshifts. The offset between the host center and the burst position, 470 ± 310 pc, is the smallest to date. Combined with the old stellar population age, this indicates that the burst likely originated from a progenitor with no significant kick velocity. However, from the brightness of the optical afterglow we infer a relatively low density of n ∼ 3 x 10-4 ε-3e,-1ε-1.75B,-1 cm-3. The combination of an optically faint afterglow and host suggests that previous such events may have been missed, thereby potentially biasing the known short GRB host population against z ∼> 1 early-type hosts.
[en] The effective recombination rate of a helium afterglow plasma, which is optically thick towards the resonance lines, is calculated from the coupled rate equations for the number densities of free electrons and of metastable atoms or molecules. The model employed is a neutral plasma, consisting of one kind of ions and one kind of metastables. The ions are lost by electron-ion recombination only, with subsequent formation of metastables, which are then deactivated in collisions with free electrons or with other metastables: in the latter case one electron is regained to the free state. When the rate constants for these various processes are time-independent, it is found that after a certain transition time a transient equilibrium between the number densities of electrons and metastables is attained. In a dense afterglow plasma, where the recombination coefficient may be large, the transient equilibrium density of metastables may become significantly higher than the qua si-equilibrium value obtained by equating the time derivative of the metastable density to zero, and the effective recombination coefficient may be reduced by much more than a factor of two
[en] GRB 100418A is a long gamma-ray burst (GRB) at redshift z = 0.6235 discovered with the Swift Gamma-ray Burst Explorer with unusual optical and X-ray light curves. After an initial short-lived, rapid decline in X-rays, the optical and X-ray light curves observed with Swift are approximately flat or rising slightly out to at least ∼7 x 103 s after the trigger, peak at ∼5 x 104 s, and then follow an approximately power-law decay. Such a long optical plateau and late peaking is rarely seen in GRB afterglows. Observations with Rapid Eye Mount during a gap in the Swift coverage indicate a bright optical flare at ∼2.5 x 104 s. The long plateau phase of the afterglow is interpreted using either a model with continuous injection of energy into the forward shock of the burst or a model in which the jet of the burst is viewed off-axis. In both models the isotropic kinetic energy in the late afterglow after the plateau phase is ≥102 times the 1051 erg of the prompt isotropic gamma-ray energy release. The energy injection model is favored because the off-axis jet model would require the intrinsic T90 for the GRB jet viewed on-axis to be very short, ∼10 ms, and the intrinsic isotropic gamma-ray energy release and the true jet energy to be much higher than the typical values of known short GRBs. The non-detection of a jet break up to t ∼ 2 x 106 s indicates a jet half-opening angle of at least ∼140, and a relatively high-collimation-corrected jet energy of Ejet ≥ 1052 erg.