Results and prospects on registration of reflected Cherenkov light of EAS from cosmic particles above 10^{15} eV

We give an overview of the SPHERE experiment based on detection of reflected Vavilov-Cherenkov radiation (Cherenkov light) from extensive air showers in the energy region E>10^{15} eV. A brief history of the reflected Cherenkov light technique is given; the observations carried out with the SPHERE-2 detector are summarized; the methods of the experimental datasample analysis are described. The first results on the primary cosmic ray all-nuclei energy spectrum and mass composition are presented. Finally, the prospects of the SPHERE experiment and the reflected Cherenkov light technique are given.Comment: 4 pages, 3 figures, Proc. PANIC-201

Hard X‐ray polarimetry of solar flares with BATSE

We describe a technique for measuring the polarization of hard X‐rays from solar flares based on the angular distribution of that portion of the flux which is scattered off the top of the Earth’s atmosphere. The scattering cross section depends not only on the scatter angle itself, but on the orientation of the scatter angle with respect to the incident polarization vector. Consequently, the distribution of the observed albedo flux will depend on the direction and the polarization properties (i.e., the level of polarization and polarization angle) of the source. Since the albedo component can represent a relatively large fraction (up to 40%) of the direct source flux, there will generally be sufficient signal for making such a measurement. The sensitivity of this approach is therefore dictated by the effective area and the ability of a detector system to ‘image’ the albedo flux. The 4π coverage of the BATSE detectors on the Compton Gamma‐RayObservatory provides an opportunity to measure both the direct and the albedo flux from a given solar flare event. Although the BATSE design (with its large field‐of‐view for each detector) is not optimized for albedo polarimetry, we have nonetheless investigated the feasibility of this technique using BATSE data

Using BATSE to measure gamma-ray burst polarization

We describe a technique for measuring the polarization of hard x-rays from γ-ray bursts based on the angular distribution of that portion of the flux which is scattered off the top of the Earth’s atmosphere. The scattering cross section depends not only on the scatter angle itself, but on the orientation of the scatter angle with respect to the incident polarization vector. Consequently, the distribution of the observed albedo flux will depend on the direction and the polarization properties (i.e., the level of polarization and polarization angle) of the source. Although the BATSE design (with its large field-of-view for each detector) is not optimized for albedo polarimetry, we have nonetheless investigated the feasibility of this technique using BATSE data

Pinning of magnetic domain walls in multiferroics

The behavior of antiferromagnetic domain wall (ADW) against the background of a periodic ferroelectric domain structure has been investigated. It has been shown that the structure and the energy of ADW change due to the interaction with a ferroelectric domain structure. The ferroelectric domain boundaries play the role of pins for magnetic spins, the spin density changes in the vicinity of ferroelectric walls. The ADW energy becomes a periodical function on a coordinate which is the position of ADW relative to the ferroelectric domain structure. It has been shown that the energy of the magnetic domain wall attains minimum values when the center of the ADW coincides with the ferroelectric wall and the periodic ferroelectric structure creates periodic coercitivity for the ADW. The neighbouring equilibrium states of the ADW are separated by a finite potential barrier.Comment: 4 pages, 2 figure

Discovery of Pulsed X-ray Emission from the SMC Transient RX J0117.6-7330

We report on the detection of pulsed, broad-band, X-ray emission from the transient source RX J0117.6-7330. The pulse period of 22 seconds is detected by the ROSAT/PSPC instrument in a 1992 Sep 30 - Oct 2 observation and by the CGRO/BATSE instrument during the same epoch. Hard X-ray pulsations are detectable by BATSE for approximately 100 days surrounding the ROSAT observation (1992 Aug 28 - Dec 8). The total directly measured X-ray luminosity during the ROSAT observation is 1.0E38 (d/60 kpc)^2 ergs s-1. The pulse frequency increases rapidly during the outburst, with a peak spin-up rate of 1.2E-10 Hz s-1 and a total frequency change 1.8%. The pulsed percentage is 11.3% from 0.1-2.5 keV, increasing to at least 78% in the 20-70 keV band. These results establish RX J0117.6-7330 as a transient Be binary system.Comment: 17 pages, Latex, aasms, accepted for publication in ApJ Letter

Accretion disc formation around the neutron star in Be/X-ray binaries

We study the accretion on to the neutron star in Be/X-ray binaries, using a 3D SPH code and the data imported from a simulation by \citet{oka2} for a coplanar system with a short period ($P_{\rm orb}=24.3 \rm{d}$) and a moderate eccentricity $(e=0.34)$, which targeted the Be/X-ray binary 4U 0115+63. For simplicity, we adopt the polytropic equation of state. We find that a time-dependent accretion disc is formed around the neutron star regardless of the simulation parameters. In the long term, the disc evolves via a two-stage process, which consists of the initial developing stage and the later developed stage. The developed disc is nearly Keplerian. In the short term, the disc structure modulates with the orbital phase. The disc shrinks at the periastron passage of the Be star and restores its radius afterwards. The accretion rate on to the neutron star is also phase dependent, but its peak is broader and much lower than that of the mass-transfer rate from the Be disc, unless the polytropic exponent is as large as 5/3. Our simulations show that the truncated Be disk model for Be/X-ray binaries is consistent with the observed X-ray behaviour of 4U 0115+63.Comment: 13pages, 62figures, accepted to MNRAS. Revised version adds in 4 new figures, in which we have improved the English, kindly pointed out by Manson Katherine. For associated movies, see http://astro3.sci.hokudai.ac.jp/~kimi/movie.htm

Hexagonal Uniformly Redundant Arrays for Coded-Aperture Imaging

Uniformly redundant arrays are used in coded-aperture imaging, a technique for forming images without mirrors or lenses. This technique is especially important for the high energy x-ray and y-ray region above 20 keV. In this technique, a mask consisting of opaque (closed) and transparent (open) areas is placed between the photon sources to be imaged and a position sensitive detector or a detector array. Each source casts a shadow pattern of the mask or aperture onto the detector. This shadow pattern may be viewed as an encoded signal for that source direction. If each possible source code is unique, the detected composite of overlapping shadow patterns may be decoded to produce an image of the source distribution