Constraining dark matter properties with SPI

Using the high-resolution spectrometer SPI on board the International Gamma-Ray Astrophysics Laboratory ( INTEGRAL ), we search for a spectral line produced by a dark matter (DM) particle with a mass in the range  40 keV < M _DM < 14 MeV  , decaying in the DM halo of the Milky Way. To distinguish the DM decay line from numerous instrumental lines found in the SPI background spectrum, we study the dependence of the intensity of the line signal on the offset of the SPI pointing from the direction toward the Galactic Centre. After a critical analysis of the uncertainties of the DM density profile in the inner Galaxy, we find that the intensity of the DM decay line should decrease by at least a factor of 3 when the offset from the Galactic Centre increases from 0° to 180°. We find that such a pronounced variation of the line flux across the sky is not observed for any line, detected with a significance higher than 3σ in the SPI background spectrum. Possible DM decay origin is not ruled out only for the unidentified spectral lines, having low (∼3σ) significance or coinciding in position with the instrumental ones. In the energy interval from 20 keV to 7 MeV, we derive restrictions on the DM decay line flux, implied by the (non-)detection of the DM decay line. For a particular DM candidate, the sterile neutrino of mass M _DM, we derive a bound on the mixing angle.     

The modified generalized moveout approximation: a new parameter selection

Non‐hyperbolic generalised moveout approximation is a powerful tool to approximate the travel‐time function by using information obtained from two rays. The standard approach for parameter selection is using three parameters defined from zero‐offset ray and two parameters obtained from a reference ray. These parameters include the travel time and travel‐time derivatives of different order. The original parameter selection implies more fit at zero offset compared with offset from a reference ray. We propose an alternative approach for parameter selection within the frame of generalised moveout approximation by transferring more fit from the zero offset to a reference ray by changing in parameter selection. The modified approximation is tested against the original one in few analytical model examples, including the multi‐layered model.     

Reindeer in tundra ecosystems: the challenges of understanding system complexity

The resilience of tundra ecosystems is limited, with relatively few key biotic components determining the general pattern of the dynamics of these systems. Sustainable use of reindeer pastures, which are natural tundra ecosystems, should take into account interactions within the whole complex of key components. Among the most important are the small herbivorous rodents. For example, during peak densities lemmings may reduce above-ground plant biomass by 50-70%. At the same time, rapid turnover of nutrients in the form of significant amounts of potassium, phosphorus and nitrogen that lemmings excrete in urine promotes vascular plant growth. It is concluded that these kinds of studies are essential for the sustainable management of Russia's grazing lands: 1) comparative studies of productivity, biological diversity and structure of plant communities under the different pressures exerted by the main groups of herbivorous animals (reindeer and small rodents), as well as under varying levels of industrial development; 2) studies of the direct and indirect effects of herbivorous mammals on biological turnover and energy flow within the system; 3) studies of the role of industrial contamination on the turnover of nutrients in tundra ecosystems.     

Palaeogeographic Changes at Lake Chokrak on the Kerch Peninsula,Ukraine, during the Mid‐ and Late‐Holocene

This project has reconstructed the palaeogeographic and environmental evolution of Lake Chokrak on the Kerch Peninsula, Ukraine, during the mid‐ and late‐Holocene. This record has been evaluated in association with a regional archaeological data set to explore human–environment interactions over this period. The results show major changes in the palaeogeographic setting of Lake Chokrak since the 3rd millennium B.C., when the postglacial marine transgression had started to fill the study area. Microfaunal analyses reveal the long persistence of an open marine embayment that only became separated from the Sea of Azov when a sand barrier developed during the late 2nd millennium B.C. When colonizing the Black Sea region after the 8th century B.C., the Greek settlers erected a fortification with a small settlement on a promontory that was by then a peninsula‐like headland extending into the lake. The colonists abandoned their settlement at the end of the 1st millennium B.C. when the depth of the surrounding lake decreased from 1.5 m to less than 1 m. Today, Lake Chokrak dries up completely during summer. A detailed relative sea level (RSL) curve for the northern coast of Kerch has been established. Sea level reached its highest position at the present day. Since the 3rd millennium B.C., sea level continuously rose, without any of the previously postulated regression/transgression cycles. The RSL curve indicates differential subsidence rates within short distances in relatively stable areas, exceeding 40 cm per 1000 years. © 2012 Wiley Periodicals, Inc.     

Grad–Shafranov Reconstruction of Magnetic Clouds: Overview and Improvements

The Grad–Shafranov reconstruction is a method of estimating the orientation (invariant axis) and cross section of magnetic flux ropes using the data from a single spacecraft. It can be applied to various magnetic structures such as magnetic clouds (MCs) and flux ropes embedded in the magnetopause and in the solar wind. We develop a number of improvements of this technique and show some examples of the reconstruction procedure of interplanetary coronal mass ejections (ICMEs) observed at 1 AU by the STEREO, Wind, and ACE spacecraft during the minimum following Solar Cycle 23. The analysis is conducted not only for ideal localized ICME events but also for non-trivial cases of magnetic clouds in fast solar wind. The Grad–Shafranov reconstruction gives reasonable results for the sample events, although it possesses certain limitations, which need to be taken into account during the interpretation of the model results.     

Impacts as sources of the exosphere on Mercury

Chemical processes associated with meteoroid bombardment of Mercury are considered. Meteoroid impacts lead to production of metal atoms as well as metal oxides and hydroxides in the planetary exosphere. By using quenching theory, the abundances of the main Na-, K-, Ca-, Fe-, Al-, Mg-, Si-, and Ti-containing species delivered to the exosphere during meteoroid impacts were estimated. Based on a correlation between the solar photo rates and the molecular constants of atmospheric diatomic molecules, photolysis lifetimes of metal oxides and SiO are estimated. Meteoroid impacts lead to the formation of hot metal atoms (0.2-0.4 eV) produced directly during impacts and of very hot metal atoms (1-2 eV) produced by the subsequent photolysis of oxides and hydroxides in the exosphere of Mercury. The concentrations of impact-produced atoms of the main elements in the exosphere are estimated relative to the observed concentrations of Ca, assumed to be produced mostly by ion sputtering. Condensation of dust grains can significantly reduce the concentrations of impact-produced atoms in the exosphere. Na, K, and Fe atoms are delivered to the exosphere directly by impacts while Ca, Al, Mg, Si, and Ti atoms are produced by the photolysis of their oxides and hydroxides. The chemistry of volatile elements such as H, S, C, and N during meteoroid bombardment is also considered. Our conclusions about the temperature and the concentrations of impact-produced atoms in the exosphere of Mercury may be checked by the Messenger spacecraft in the near future and by BepiColombo spacecraft some years later.     

First geophysical and shallow ice core investigation of the Kazbek plateau glacier,Caucasus Mountains

First-ever ice core drilling at Mt. Kazbek (Caucasus Mountains) took place in the summer of 2014. A shallow ice core (18 m) was extracted from a plateau at ~4500 m a.s.l. in the vicinity of the Mt. Kazbek summit (5033 m a.s.l.). A detailed radar survey showed that the maximum ice thickness at this location is ~250 m. Borehole temperature of ?7 °C was measured at 10 m depth. The ice core was analyzed for oxygen and deuterium isotopes and dust concentration. From the observed seasonal cycle, it was determined that the ice core covers the time interval of 2009–2014, with a mean annual snow accumulation rate of 1800 mm w. eq. Multiple melt layers have been detected. δ¹⁸O values vary from ?25 to ?5‰. The dust content was determined using a particle sizing and counting analyzer. The dust layers were investigated using scanning electron microscopy and X-ray diffraction analysis. Dust can be separated into two categories by its origin: local and distant. Samples reflecting predominantly local origin consisted mainly of magmatic rocks, while clay minerals were a characteristic of dust carried over large distances, from the deserts of the Middle East and Sahara. The calculated average dust flux over three years at Kazbek was of 1.3 mg/cm² a^?1. Neither δ¹⁸O nor dust records appear to have been affected by summer melting. Overall, the conditions on Kazbek plateau and the available data suggest that the area offers good prospects of future deep drilling in order to obtain a unique environmental record.