118212086
A Simple Model for Galactic Cosmic Rays which is Consistent with Age and Anisotropy Data
117706405
Two-component model for cosmic-ray fluctuations at neutron monitor energies
123383571
The interplanetary transport of solar cosmic rays
Numerical solutions are presented for the propagation of solar cosmic rays in interplanetary space, including the effects of pitch-angle scattering and adiabatic focusing. The intensity-time profiles can be well fitted by a simple radial spatial diffusion equation with scattering mean-free path lambda/sub fit/. The radial mean-free path so obtained is significantly larger than the true scattering mean-free path for low-rigidity particles due to both adiabatic focusing and the inapplicability of the diffusive approximation early in the event. The well-known discrepancy between lambda/sub fit/ and the theoretical predictions may be resolved by these calculations.
121844770
The age distribution of galactic cosmic rays
The general solution for the distribution of ages for primary galactic cosmic rays is given for a class of steady-state, bounded models of cosmic-ray diffusion in the Galaxy. Both one-and threedimensional models are considered, with point sources and distributed sources. In all models, the age distribution, is approximately exponential for ages longer than the average age, although for shorter ages the distribution depends on the details of the model. The leaky-box model, with an exponential age distribution, is thus a good approximation to most diffusive models. It is shown that one-dimensional (‘disk’) models are consistent with both age and anisotropy data for galactic cosmic rays regardless of whether production takes place near the galactic center or throughout the disk.
7722527
Low-energy line emission from Cygnus X-2 observed by the BeppoSAX LECS
We present a 0.2–10 keV spectrum of the low-mass X-ray binary Cygnus X-2 obtained using the Low Energy Concentrator Spectrometer on-board BeppoSAX. The spectrum can be described by a cut-off power-law model with absorption of (2.28±0.07)×1021 atoms cm−2, a power-law index of 0.78±0.02 and a cut-off energy of 4.30±0.08 keV (68% confidence errors), except at energies near ∼1 keV where excess emission is present. This can be modeled by a broad Gaussian line feature with an energy of 1.02±0.04 keV, a full width half-maximum of 0.47±0.07 keV and an equivalent width of 74±1125 eV. This result confirms earlier reports of line emission near 1 keV and shows the intensity and structure of the feature to be variable. For a more detailed account of these observations we refer to Kuulkers et al. [4].
123408840
Effect of prolonged annealing on the performance of coaxial Ge gamma-ray detectors.
The effects of prolonged annealing at elevated temperatures have been investigated in a 53cm3 closed-end coaxial high purity germanium detector in the reverse electrode configuration. The detector was multiply annealed at 100°C in block periods of 7 days. After each anneal cycle it was cooled to 77 K and the relative efficiency, peak channel location and FWHM energy resolution measured at 6 gamma-ray energies. At the present time, the detector has completed 16 anneal cycles. It was found that above ~ 662 keV the photopeak efficiency decreased almost linearly at a rate of ~ 1.5% per anneal cycle, although the energy resolution and centroid (and therefore charge collection efficiency) remained unchanged. The change in detection efficiency is attributed to the expansion of the inner n+ contact due to the thermal drive-in of Li ions into the bulk. The rate is found to follow a power-law dependence in agreement with that expected from Fick's diffusion laws. Using these data, we have derived a simple 1-D phenomenological model in which the n+ contact thickness is simply related to the Li diffusion length. For annealing at 100°C, the thickness of the n+ contact, d, as a function of the annealing time, t, can be described semi-empirically by d(mm) = 0.231 × t(days)1/2.
121516202
An inexpensive spectroscopic beam monitor for hard X-ray synchrotron applications
We describe an inexpensive beam monitor for hard X-ray synchrotron applications which has good spectroscopic abilities and can operate without cooling. The device is centred on an inexpensive, commercial off-the-shelf, large area (1.2 × 1.2 mm2) Si photodiode operated in single counting mode. Measurements carried out at the HASYLAB synchrotron research facility have shown that it is fully spectroscopic across the energy range 8 keV to 100 keV with a measured energy resolution of ~ 1.2 keV FWHM at room temperature. The measured resolutions were found to be the same under pencil-beam and full-area illumination, indicating uniform crystallinity and stoichiometry of the bulk. The low cost, simplicity and performance of the detector make it suitable for a wider range of applications, e.g., in undergraduate laboratory experiments.
14794021
BeppoSAX Observations of GRB 980425: Detection of the Prompt Event and Monitoring of the Error Box
We present BeppoSAX follow-up observations of GRB 980425 obtained with the Narrow Field Instruments (NFI) in 1998 April, May, and November. The first NFI observation has detected within the 8' radius error box of the gamma-ray burst (GRB) an X-ray source positionally consistent with the supernova 1998bw, which exploded within a day of GRB 980425, and a fainter X-ray source, not consistent with the position of the supernova. The former source is detected in the following NFI pointings and exhibits a decline of a factor of 2 in six months. If it is associated with SN 1998bw, this is the first detection of X-ray emission from a Type I supernova above 2 keV. The latter source exhibits only marginally significant variability. The X-ray spectra and variability of the supernova are compared with thermal and nonthermal models of supernova high-energy emission. Based on the BeppoSAX data, it is not possible to establish firmly which of the two detected sources is the GRB X-ray counterpart, although probability considerations favor the supernova.
12240573
Evidence for Dust-related X-Ray Emission from Comet C/1995 O1 (Hale-Bopp)
We report the discovery of X-ray emission from comet C/1995 O1 (Hale-Bopp) by the LECS instrument on board BeppoSAX on 1996 September 10-11. The 0.1-2.0 keV luminosity decayed by a factor of 2 on a timescale of ~10 hr with a mean value of 5×1016 ergs s−1. The spectrum is well fitted by a thermal bremsstrahlung model with a temperature of 0.29±0.06 keV or a power law with a photon index of 3.1+ 0.6−0.2. The lack of detected C and O line emission places severe constraints on many models for cometary X-ray emission, especially those that involve X-ray production in cometary gas. The luminosity is a factor of at least 3.4 greater than measured by the Extreme Ultraviolet Explorer (EUVE) 4 days later. This difference may be related to the emergence from the nucleus on 1996 September 9 of a dust-rich cloud. Over the next few days, the cloud continued to expand, becoming increasingly tenuous until it had reached an extent of ~3×105 km (or ~2') by the start of the EUVE observation. We speculate that the observed reduction in X-ray intensity is evidence for dust fragmentation. These results support the view that cometary X-ray emission arises from the interaction between solar X-rays and cometary dust.