Inferring the emission regions for different kinds of gamma‐ray bursts

Using a theoretical model describing pulse shapes, we have clarified the relations between the observed pulses and their corresponding timescales, such as the angular spreading time, the dynamic time as well as the cooling time. We find that the angular spreading timescale caused by curvature effect of fireball surface only contributes to the falling part of the observed pulses, while the dynamic one in the co‐moving frame of the shell merely contributes to the rising portion of pulses provided the radiative time is negligible. In addition, the pulses resulted from the pure radiative cooling time of relativistic electrons exhibit properties of fast rise and slow decay (a quasi‐FRED) profile together with smooth peaks. Besides, we interpret the phenomena of wider pulses tending to be more asymmetric to be a consequence of the difference in emission regions. Meanwhile, we find the intrinsic emission time is decided by the ratios of lorentz factors and radii of the shells between short and long bursts. Based on the analysis of asymmetry, our results suggest that the long GRB pulses may occur in the regions with larger radius, while the short bursts could locate at the smaller distance from central engine. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Non-singular cosmology using tachyon and general non-minimal kinetic coupling

The bounce with non-minimal coupling is very interesting topic because in the early time, general relativity is likely to be modified, which can give some valuable effects to the evolution of our universe. In this paper we introduce a string-inspired model for bouncing universe, utilizing the tachyon field as well as contributions from general non-minimal kinetic couplings and curvature. It is shown numerically that the bouncing solution appears in the model whereas the equation of state (EoS) parameter crosses the phantom divider.     

On the impact of the Yarkovsky effect on Apophis’ orbit

In October 2009, a new set of optical observations of Apophis, a potentially hazardous asteroid, was published. These data have significantly expanded the interval of observations and their total number. In the article we compare the results of refinement of Apophis’ orbit made at the Jet Propulsion Laboratory (JPL, United States), the University of Pisa (Italy), and the Institute of Applied Astronomy (IAA) of the Russian Academy of Sciences with consideration for new observations. New orbits lead to a significant decrease in the probability of Apophis’ collision with the Earth in 2036. As a result of processing a large number of observations of asteroids approaching the Earth and main belt asteroids less than 40 km in size, with a large number of optical and, in many cases, radar observations in different oppositions, one of the authors revealed that additional acceleration affects their motion. This acceleration can be represented by the transversal component A ₂ in the orbital coordinate system. The presence of this acceleration can be interpreted as the Yarkovsky effect. The statistical properties of distribution of A ₂ for asteroids, for which it is determined quite reliably, evidence in favor of this interpretation. The value of additional acceleration for bodies the size of Apophis falls in the range ±10⁻¹³ AU/day². In this paper we have calculated the probability of Apophis colliding with the Earth in 2036 at different values of the transversal component of additional acceleration A ₂. For the resulting points, a plot of the probability of the collision against the A ₂ value has been constructed. At A ₂ = −8.748 × 10⁻¹⁴ AU/day² (and zero values of the radial A ₁ and normal A ₃ components) the nominal solution for Apophis’ orbit on April 13, 2029, is only 90 m from the middle of a “keyhole” 600 m in width, which leads to a collision of Apophis with the Earth in 2036. Since the scattering ellipse in the target plane in 2029 significantly overlaps the keyhole, the probability of collision at the given additional acceleration value is 0.0022. This result has been verified by the Monte Carlo method. Tests of 10000 random sets of orbital elements, which were found taking into account their correlation, have shown that 22 cases have resulted in virtual asteroids colliding with Earth in 2036. A plot of the probability of the collision against the value of A ₂ has been constructed.     

Dust extinction and X-ray emission from the starburst galaxy NGC 1482

We present the results based on multiwavelength imaging observations of the prominent dust lane starburst galaxy NGC 1482 aimed to investigate the extinction properties of dust existing in the extreme environment. (B-V) colour-index map derived for the starburst galaxy NGC 1482 confirms two prominent dust lanes running along its optical major axis and are found to extend up to ∼11 kpc. In addition to the main lanes, several filamentary structures of dust originating from the central starburst are also evident. Though, the dust is surrounded by exotic environment, the average extinction curve derived for this target galaxy is compatible with the Galactic curve, with R_V = 3.05, and imply that the dust grains responsible for the optical extinction in the target galaxy are not really different than the canonical grains in the Milky Way. Our estimate of total dust content of NGC 1482 assuming screening effect of dust is ∼2.7 × 10⁵ M_⊙, and provide lower limit due to the fact that our method is not sensitive to the intermix component of dust. Comparison of the observed dust in the galaxy with that supplied by the SNe to the ISM, imply that this supply is not sufficient to account for the observed dust and hence point towards the origin of dust in this galaxy through a merger like event.Our multiband imaging analysis reveals a qualitative physical correspondence between the morphologies of the dust and Hα emission lines as well as diffuse X-ray emission in this galaxy. Spatially resolved spectral analysis of the hot gas along outflows exhibit a gradient in the temperature. Similar gradient was also noticed in the measured values of metallicity, indicating that the gas in the halo is not yet enriched. High resolution, 2-8 keV Chandra image reveals a pair of point sources in the nuclear region with their luminosities equal to 2.27 × 10³⁹ erg s⁻¹ and 9.34 × 10³⁹ erg s⁻¹, and are in excess of the Eddington-limit of 1.5 M_⊙ accreting source. Spectral analysis of these sources exhibit an absorbed-power law with the hydrogen column density higher than that derived from the optical measurements.     

The Asymmetrical Eruption of a Quiescent Filament and Associated Halo CME

We will present detailed observations of the asymmetrical eruption of a large quiescent filament on 24 November 2002, which was followed by a two-ribbon flare, three coronal dimmings, endpoint brightenings, and a very fast halo-type coronal mass ejection (CME). Before the eruption, the filament lay along the main neutral line (MNL) underneath a single-arcade helmet streamer with a simple bipolar configuration. However, photospheric magnetic fields on both sides of the filament showed an asymmetrical distribution, and the filament and MNL were not located just at the center of the streamer base but were closer to the eastern leg of the streamer arcade. Therefore, instead of erupting along the streamer’s symmetrical axis, the filament showed a nonradial and asymmetrical eruption. It lifted from the eastern flank of the streamer arcade to impact the western leg directly, leading to an asymmetrical CME that expanded westward; eventually the streamer was disrupted significantly. Accordingly, the opposite-polarity coronal dimmings at both sides of the filament forming in the eruption also showed an asymmetrical area distribution. We thus assume that the streamer arcade could guide the filament at the early eruption phase but failed to restrain it later. Consistent with previous results, these observations suggest that the global background magnetic field can impose additional action on the initial eruption of the filament and CME, as well as the dimming configuration.     

Production of krypton and xenon isotopes in thick stony and iron targets isotropically irradiated with 1600 MeV protons

Abstract— Two spherical targets made of gabbro with a radius of 25 cm and of steel with a radius of 10 cm were irradiated isotropically with 1600 MeV protons at the SATURNE synchrotron at Laboratoire National Saturne (LNS)/CEN Saclay, in order to simulate the production of nuclides in meteorites induced by galactic cosmic‐ray protons in space. These experiments supply depth‐dependent production rate data for a wide range of radioactive and stable isotopes in up to 28 target elements. In this paper, we report results for ⁷⁸Kr, ^80–86Kr isotopes in Rb, Sr, Y and Zr and for ¹²⁴Xe, ¹²⁶Xe, ^128–132Xe, ¹³⁴Xe, ¹³⁶Xe isotopes in Ba and La. Krypton and xenon concentrations have been measured at different depths in the spheres by using conventional mass spectrometry. Based on Monte‐Carlo techniques, theoretical production rates are calculated by folding depth‐dependent spectra of primary and secondary protons and secondary neutrons with the excitation functions of the relevant nuclear reactions. The comparison of the model calculation results with experimental data in the thick target experiments performed at LNS and previously at CERN have allowed adjustments of the poorly known excitation functions of neutron‐induced reactions. Thus, for the two experiments at SATURNE, excellent agreement is obtained between experimental and calculated production rates for most Kr and Xe isotopes in all investigated target elements. Only Xe production in Ba in the gabbro is underestimated by the calculations by ?25%. This work validates the approach of the thin‐target model calculations of cosmogenic nuclide production rates in the attempt of modeling the interaction of galactic cosmic‐ray protons with stony and iron meteorites in space as well as with lunar samples.     

The Dar al Gani meteorite field (Libyan Sahara): Geological setting,pairing of meteorites,and recovery density

Abstract— As of July 2001, 1238 Libyan meteorites have been reported. Most were found in two areas called Dar al Gani and Hamadah al Hamra. Dar al Gani is located on a plateau of marine carbonate rocks with marly components. Eight‐hundred and sixty‐nine meteorites between 6 g and 95 kg totalling 687 kg have been found here but the calculated mean recovery density is comparatively low with one meteorite on 6.5 km². Dar al Gani is a perfect site for the recognition and preservation of meteorites. The existence of meteorites is the result of a combination of specific geological and geomorphological conditions: there is a bright‐colored, old limestone plateau (<2 Ma), under arid weather conditions over long periods of time, with rapid elimination of surface water if present and low erosion rates. The preservation of meteorites is guaranteed through the absence of quartz sand on the plateau, strongly reducing wind erosion and a basic environment emerging from the carbonate ground retards rusting of metallic meteorite components. A supposed soil cover during pluvial times has probably protected older meteorites and led to a concentration of meteorites of different periods. An evaluation of Dar al Gani meteorites suggests the existence of at least 26 strewnfields and 26 meteorite pairs reducing the number of falls to, at most, 534. Shock and weathering grades as a tool for the recognition of pairings turned out to be problematic, as several strewnfields showed paired meteorites which had been classified to different shock and weathering grades.     

Formation of proton fluxes under the radiation belts during geomagnetic disturbances

The fluxes of energetic particles under the radiation belts are studied using data obtained in the experiments onboard the CORONAS-I and CORONAS-F satelites. The spatial structure of the distributions of proton fluxes with E _p > 1 MeV both near the geomagnetic equator on L ≤ 1.2 and at high latitudes on L ～ 3.5–6.5 as well as the particle flux variations with geomagnetic activity are analyzed. The scattering processes that lead to particle precipitation and, in particular, the scattering of protons as they interact with VLF emission and the scattering when the particle motion becomes nonadiabatic are considered. We compare the data on particle dynamics during geomagnetic disturbances of various kinds to determine whether the physical processes that lead to particle precipitation are a manifestation of the geoefficiency of a given magnetic storm or they are controlled by internal magnetospheric conditions.     

CCD Polarimetric Imaging Of Comet Hale-Bopp (C/1995 O1)

Polarimetric observations of the light scattered by dust have been carried out at Pic-du-Midi Observatory with the 2 m telescope in June and September–October 1996, and at Haute-Provence Observatory with the 0.80 m telescope in April 1997. They cover a total number of 11 nights and a large (6.9°–47.7°) phase angle range. The spatial resolution allows to underline structures in the coma, as well in the brightness images as in the polarization maps, with a correlation between the regions of bright structures and the regions of higher polarization. A clear difference appears between the sunward and antisunward side, with higher polarization on the antisunward side. The phase angle coverage allows us to obtain a polarimetric phase curve for the whole coma and to compare it with other cometary phase curves. The degree of polarization is higher for Hale-Bopp than for the comets previously observed. This revised version was published online in July 2006 with corrections to the Cover Date.