Unveiling soft gamma-ray repeaters with INTEGRAL

Thanks to INTEGRAL’s long exposures of the Galactic Plane, the two brightest Soft Gamma-Ray Repeaters, SGR 1806-20 and SGR 1900+14, have been monitored and studied in detail for the first time at hard-X/soft gamma rays. This has produced a wealth of new scientific results, which we will review here. Since SGR 1806-20 was particularly active during the last two years, more than 300 short bursts have been observed with INTEGRAL and their characteristics have been studied with unprecedented sensitivity in the 15–200 keV range. A hardness-intensity anticorrelation within the bursts has been discovered and the overall Number-Intensity distribution of the bursts has been determined. In addition, a particularly active state, during which 100 bursts were emitted in 10 minutes, has been observed on October 5 2004, indicating that the source activity was rapidly increasing. This eventually led to the Giant Flare of December 27th 2004, for which a possible soft gamma-ray (>80 keV) early afterglow has been detected. The deep observations allowed us to discover the persistent emission in hard X-rays (20–150 keV) from 1806-20 and 1900+14, the latter being in a quiescent state, and to directly compare the spectral characteristics of all Magnetars (two SGRs and three Anomalous X-ray Pulsars) detected with INTEGRAL. D.G. acknowledges the French Space Agency (CNES) for financial support. Based on observations with INTEGRAL, an ESA project with instruments and the science data centre funded by ESA member states (especially the PI countries: Denmark, France, Germany, Italy, Switzerland, Spain), Czech Republic and Poland, and with the participation of Russia and the USA. ISGRI has been realized and maintained in flight by CEA-Saclay/DAPNIA with the support of CNES. K.H. is grateful for support under NASA’s INTEGRAL U.S. Guest Investigator program, Grants NAG5-13738 and NNG05GG35G.     

Area and volume computation of longitude–latitude grids and three‐dimensional meshes

Longitude–latitude grids are commonly used for surface analyses and data storage in GIS. For volumetric analyses, three‐dimensional meshes perpendicularly raised above or below the gridded surface are applied. Since grids and meshes are defined with geographic coordinates, they are not equal area or volume due to convergence of the meridians and radii. This article compiles and presents known geodetic considerations and relevant formulae needed for longitude–latitude grid and mesh analyses in GIS. The effect of neglecting these considerations is demonstrated on area and volume calculations of ecological marine units.     

Stability analysis of the martian obliquity during the Noachian era

We performed numerical simulations of the obliquity evolution of Mars during the Noachian era, at which time the giant planets were on drastically different orbits than today. For the preferred primordial configuration of the planets we find that there are two large zones where the martian obliquity is stable and oscillates with an amplitude lower than 20°. These zones occur at obliquities below 30° and above 60°; intermediate values show either resonant or chaotic behaviour depending on the primordial orbits of the terrestrial planets.     

Isotopic and elemental fractionation of solar wind implanted in the Genesis concentrator target characterized and quantified by noble gases

Abstract– We report concentrations and isotopic compositions of He, Ne, and Ar measured with high spatial resolution along a radial traverse of a silicon carbide (SiC) quadrant of the Genesis mission concentrator target. The Ne isotopic composition maps instrumental fractionation as a function of radial position in the target: the maximum observed isotopic fractionation is approximately 33‰ per mass unit between the center and periphery. The Ne fluence is enhanced by a factor of 43 at the target center and decreases to 5.5 times at the periphery relative to the bulk solar wind fluence. Neon isotopic profiles measured along all four arms of the “gold cross” mount which held the quadrants in the concentrator target demonstrate that the concentrator target was symmetrically irradiated during operation as designed. We used implantation experiments of Ne into SiC and gold to quantify backscatter loss and isotopic fractionation and compared measurements with numerical simulations from the code “stopping and range of ions in matter.” The ²⁰Ne fluence curve as a function of radial distance on the target may be used to construct concentration factors relative to bulk solar wind for accurate corrections for solar wind fluences of other light elements to be measured in the concentrator target. The Ne isotopic composition as a function of the radial distance in the SiC quadrant provides a correction for the instrumental mass‐dependent isotopic fractionation by the concentrator and can be used to correct measured solar wind oxygen and nitrogen isotopic compositions to obtain bulk solar wind isotopic compositions.     

Structural and isotopic microanalysis of presolar SiC from supernovae

Abstract– We report on the microstructure, crystallography, chemistry, and isotopic compositions of seven SiC X grains and two mainstream grains from the Murchison meteorite. TEM crystallographic analysis revealed that the X grains (approximately 3 μm) are composed of many small crystals (24–457 nm), while the similarly sized mainstream grains are composed of only a few crystals (0.5–1.7 μm). The difference in crystal size likely results from differences in their formation environments: the X grain crystals evidently formed under conditions of greater supersaturation and rapid growth compared to their mainstream counterparts. However, the same polytypes are observed in both mainstream and X grains. Six X grains and both mainstream grains are entirely the 3C‐SiC polytype and one X grain is an intergrowth of the 3C‐SiC and 2H‐SiC polytypes. EDXS measurements indicate relatively high Mg content in the X grains (≲5 atomic%), while Mg was undetectable in the mainstream grains. The high Mg content is probably from the decay of ²⁶Al into ²⁶Mg. Estimates of the ²⁶Al/²⁷Al ratios, which range from 0.44–0.67, were made from elemental Mg/Al ratios. This range is consistent with the ²⁶Al/²⁷Al ratios inferred from previous isotopic measurements of X grains. We also report the first direct observations of subgrains in X grains, including the first silicides [(Fe,Ni)_nSi_m]. Diffraction data do not match any previously observed presolar phases, but are a good fit to silicides, which are predicted stable SN condensates. Eight subgrains with highly variable Ni/Fe ratios (0.12–1.60) were observed in two X grains.     

Evaluating techniques for sampling stream crayfish (Paranephrops planifrons)

We evaluated several capture and analysis techniques for estimating abundance and size structure of freshwater crayfish (Paranephrops planifrons) (koura) from a forested North Island, New Zealand stream to provide a methodological basis for future population studies. Direct observation at night and collecting with baited traps were not considered useful. A quadrat sampler was highly biased toward collecting small individuals. Handnetting at night and estimating abundances using the depletion method were not as efficient as handnetting on different dates and analysing by a mark‐recapture technique. Electrofishing was effective in collecting koura from different habitats and resulted in the highest abundance estimates, and mark‐recapture estimates appeared to be more precise than depletion estimates, especially if multiple recaptures were made. Handnetting captured more large crayfish relative to electrofishing or the quadrat sampler.