Pulsar studies with GRO-COMPTEL

Pulsar measurements performed by the experiment COMPTEL, aboard the Compton Gamma Ray Observatory, are described. The main results refer to the Crab and Vela pulsars whose pulse shape characteristics are given in some detail and light curves are compared with those above 50 MeV, as observed by the COS-B satellite. No other gamma-ray pulsars have been detected to date by COMPTEL, the upper limit on the pulsed signal from Geminga being compatible with indications by other experiments.     

Aura/MLS与TIMED/SABER观测全球重力波特性

大气重力波是临近空间环境主要大气波动之一,对全球环流具有重要影响。卫星上搭载的临边探测器能够探测临近空间大气温度,可用于临近空间大气重力波研究。利用2012－2014年Aura的微波临边探测器（MLS）和TIMED的红外临边探测器（SABER）的探测数据,对20~50 km高度的大气重力波扰动分布特征开展了分析研究,两种观测重力波活动基本一致,重力波随季节、纬度及高度的变化显著。冬季半球高纬度重力波扰动较强,赤道和夏季半球近赤道地区上空也存在明显重力波活动区域,夏季半球高纬度重力波扰动最弱。重力波扰动强度随高度增加。TIMED/SABER重力波扰动强度数值比 Aura/MLS略强。      

Multiple Coulomb scattering method to reconstruct low-energy gamma–ray direction in the GAMMA-400 space-based gamma–ray telescope

The GAMMA-400 currently developing space-based gamma-ray telescope is designed to measure the gamma-ray fluxes in the energy range from ～20?MeV to several TeV in the highly elliptic orbit (without shadowing the telescope by the Earth) continuously for a long time. The physical characteristics of the GAMMA-400 gamma-ray telescope, especially the angular and energy resolutions (at 100-GeV gamma rays they are ～0.01° and ～1%, respectively), allow us to consider this space-based experiment as the next step in the development of extraterrestrial high-energy gamma-ray astronomy. In this paper, a method to improve the reconstruction accuracy of incident angle for low-energy gamma rays in the GAMMA-400 space-based gamma-ray telescope is presented. The special analysis of topology of pair-conversion events in thin layers of converter was performed. Applying the energy dependence of multiple Coulomb scattering for pair components, it is possible to estimate the energies for each particle, and to use these energies as weight in the angle reconstruction procedure. To identify the unique track in each projection the imaginary curvature method is applied. It allows us to obtain significantly better angular resolution in comparison with other methods applied in current space-based experiments. When using this method for 50-MeV gamma rays the GAMMA-400 gamma-ray telescope angular resolution is about 4°.     

High precision gamma-ray spectrometer PGS for Russian interplanetary mission to Mars

The high precision gamma-ray spectrometer (PGS) is scheduled to be launched on the Russian MARS mission in 1996, and to go into an elliptical polar orbit around Mars. The PGS consists of two high-purity germanium detectors, associated electronics, and a passive cooler and will be deployed from one of the solar panels. The PGS will measure nuclear gamma-ray emissions from the Martian surface, cosmic gamma-ray bursts, and the high-energy component of solar flares in the broad energy range from 50 keV to 8 MeV in 4096 energy channels. The first results are presented of development, integration and qualification of the instrument, both for the passive cooler and for the detector with spectrometric electronics.     

Low and medium energy gamma-ray astronomy — present status and future aspects

During the last few years quite some progress has been achieved in the field of low and medium energy gamma-ray astronomy below about 30 MeV. Gamma rays from the galactic center and anti-center region have been detected, which require a high interstellar electron flux in the 100 MeV range, if they are predominantly diffuse in nature. Though the Crab pulsar and its nebula are still the only galactic gamma-ray sources which definitely have been detected, some recently determined upper limits to the gamma-ray fluxes of other radio pulsars are close to the theoretically expected values. Active galaxies seem to have a maximum of luminosity in the range between several 100 keV and a few MeV and, therefore, are of special interest. First observational results have been reported on the Seyfert galaxies NGC 4151 and MCG 8-11-11, and the radio galaxy CenA. The nature of the diffuse cosmic gamma-ray component at low gamma-ray energies is not yet solved. Unresolved active galaxies are good candidates for its origin.Considering the present status of gamma ray astronomy the study of galactic sources like radio pulsars and the unidentified high energy gamma-ray sources, the Milky Way as a whole, active galaxies and the diffuse cosmic sky seem to be the prime targets for broad band observations below 30 MeV in the GRO area. An unexplored field like that of low energy gamma-ray astronomy, however, is always open for surprises.     

Solar-flare neutrons and gamma rays

Calculations of neutron and gamma-ray production in solar flares are reviewed and compared with neutron and gamma-ray data from the 21 June 1980 and 3 June 1982 flares, as well as gamma-ray data from other flares. The implied charged-particle numbers and spectra are compared with interplanetary observations.     

Acceleration reactions of cells and tissues--their genetic-phylogenic implications.

This paper speculates about the interplay between adaptational modifications with mutation and selection. Gravity effects are supposed to be very well suited to prove the role of direct adaptations for phylogenic processes. The speculation is based on strong hints that the cell in general reacts to accelerations (besides other mechanical stimuli) in the order of 1g and near weightlessness. Several-generations experiments in space may contribute to solve this fundamental question of evolution.     

Gamma-ray spectroscopy: Status and prospects

Contemporary gamma-ray spectroscopy instruments and their results are reviewed. Sensitivities of 10^?4 to 10^?3 ph/cm²-sec have been achieved for steady sources and 10^?2 to 1 ph/cm²-sec for transient sources. This has led to the detection of gamma-ray lines from more than 40 objects representing 6 classes of astrophysical phenomena. The lines carry model-independent information and are of fundamental importance to theoretical modeling and our understanding of the objects. These results indicate that gamma-ray spectroscopy is relevant to a wide range of astrophysical problems and is becoming a major part of astronomy. The objectives and anticipated results of future instruments are discussed. Several instruments in development will have a factor of ～ 10 sensitivity improvement to certain phenomena over contemporary instruments. A factor of ～ 100 improvement in sensitivity will allow the full potential of gamma-ray spectroscopy to be realized. Instrument concepts which would achieve this with both present and advanced techniques are discussed.     

GPS-only gravity field recovery with GOCE,CHAMP, and GRACE

Gravity missions such as the Gravity field and steady-state Ocean Circulation Explorer (GOCE) are equipped with onboard Global Positioning System (GPS) receivers for precise orbit determination (POD), instrument time-tagging, and the extraction of the long wavelength part of the Earth’s gravity field. The very low orbital altitude of the GOCE satellite and the availability of dense 1 s GPS tracking data are ideal characteristics to exploit the contribution of GPS high-low Satellite-to-Satellite Tracking (hl-SST) to gravity field determination. We present gravity field solutions based on about 8 months of GOCE GPS hl-SST data from 2009 and compare the results with those obtained from the CHAllenging Minisatellite Payload (CHAMP) and Gravity Recovery And Climate Experiment (GRACE) missions. The very low orbital altitude of GOCE significantly improves gravity field recovery from GPS hl-SST data above degree 20, but not for the degrees below 20, where the quality of the spherical harmonic coefficients remains essentially unchanged. Despite the limited time span of GOCE data used, the gravity field of the Earth can be resolved up to about degree 115 using GPS data only. Empirically determined phase center variations (PCVs) of the GOCE onboard GPS helix antenna are, however, mandatory to achieve this performance.     

The low energy gamma-ray experiments on GRO in perspective

The NASA Gamma-Ray Observatory, GRO, will carry two instruments for low energy gamma-ray astronomy. The ‘Oriented Scintillation Spectrometer Experiment - OSSE’ represents the latest step in the evolution of collimated detectors. A large detection area, simultaneous source and background observation and rigorous control over systematic errors yield significant improvements in sensitivity over earlier instruments. The ‘Imaging Compton Telescope - COMPTEL’ brings the proven concept of the Compton telescope to the state of the art level. Position sensitive scintillation detectors make it possible to generate sky images with a resolution of about 2° over a f.o.v. of about 1 sr. The complementary nature of these two experiments promises a first in-depth exploration of the sky in a wavelength range which covers the transition from the X-ray sky to the apparently unrelated high energy gamma-ray sky. Possible directions of further evolution of these experiments will be discussed.     

Radio-faint BL Lac objects and their impact on the radio/gamma-ray connection

Radio and gamma-ray emissions in Active Galactic Nuclei (AGNs) are both related to the presence of relativistic particles in jets. With the advent of the Fermi Large Area Telescope (LAT), and thanks to its large sensitivity up to several GeV, many observational results are changing our understanding of these phenomena. BL Lac objects, which made up only a fraction of the known extragalactic gamma-ray source population before Fermi, have now become the most abundant class. However, since they are relatively weak radio sources, most of them are poorly known as far as their parsec scale structure and multi-wavelength properties are concerned. For this reason, we have selected a complete sample of 42 low redshift BL Lacs (independently of their gamma-ray properties) to study with a multi-wavelength (radio, optical, X-ray, gamma-ray) approach. Here, we present results and images of sources in the sample (most of which have never been observed before), using new VLBA observations at 8 and 15 GHz. Beyond this sample of BL Lacs, the population of gamma-ray AGNs has also dramatically enlarged in the Fermi era, permitting us to discuss the presence of a correlation between radio and gamma-ray properties with improved statistical significance. We explore the radio-gamma relation with several hundreds sources and using both simultaneous and archival radio data, thus tackling the impact of time variability.     

CORONAS-F observations of active phenomena on the sun

Complex observations in the framework of the CORONAS-F Mission aimed at the study of active phenomena inthe solar corona are described. The main features are given for the following experiments: (1) XUV-imaging spectroscopy with high temporal and spatial resolution, (2) X-ray spectroscopy, (3) X-ray and gamma-ray photometer/spectrometer, and (4) solar cosmic rays. Some new observational data on the structure and dynamics of flares and transient events are discussed along with their analysis.     

The reaction of Xenopus laevis Daudin (South African toad) to linear accelerations.

Preparing the German Spacelab Mission D-2 project "Gravity Perception and Neuronal Plasticity"--STATEX II--ground based experiments have been performed with larvae of the amphibian vertebrate Xenopus laevis Daud. to study the reactions to different levels of acceleration forces and profiles. The larvae have been exposed to accelerations of up to 5 g for different time periods using a modified laboratory centrifuge and the NIZEMI (Niedergeschwindigkeits-Zentrifugen-Mikroskop) which allows direct observation and video documentation. The results will be discussed and compared with those of the D1-Mission, parabolic flights, and simulated weightlessness.     

Investigating gamma-ray burst data reduction techniques with Swift’s instruments

The amount of data on gamma-ray bursts (GRBs) and the detected afterglows observed by the Swift satellite contributed significantly to the understanding of the phenomenon. The behavior of the early afterglow rises some interesting questions. With the early afterglow localizations of gamma-ray burst positions made by Swift, the clear delimitation of the prompt phase and the afterglow is not so obvious any more. There are hints of a canonical X-ray afterglow lightcurve with segments of different slopes. Not all bursts necessarily show all the segments. It is important to see if the prompt phase and the afterglow has the same origin or they stem from different parts of the progenitor system. We will combine the of gamma-ray burst data from BAT and XRT and compare the extrapolated gamma-ray flux to the X-ray in a sample of bursts and find that there is a good agreement between the two measurements. This indicates that the physical process shaping burst and the early afterglow are the same.     

Insects as test systems for assessing the potential role of microgravity in biological development and evolution.

Gravity and radiation are undoubtedly the two major environmental factors altered in space. Gravity is a weak force, which creates a permanent potential field acting on the mass of biological systems and their cellular components, strongly reduced in space flights. Developmental systems, particularly at very early stages, provide the larger cellular compartments known, where the effects of alterations in the size of the gravity vector on living organisms can be more effectively tested. The insects, one of the more highly evolved classes of animals in which early development occurs in a syncytial embryo, are systems particularly well suited to test these effects and the specific developmental mechanisms affected. Furthermore, they share some basic features such as small size, short life cycles, relatively high radio-resistance, etc. and show a diversity of developmental strategies and tempos advantageous in experiments of this type in space. Drosophila melanogaster, the current biological paradigm to study development, with so much genetic and evolutionary background available, is clearly the reference organism for these studies. The current evidence on the effects of the physical parameters altered in space flights on insect development indicate a surprising correlation between effects seen on the fast developing and relatively small Drosophila embryo and the more slowly developing and large Carausius morosus system. In relation to the issue of the importance of developmental and environmental constraints in biological evolution, still the missing link in current evolutionary thinking, insects and space facilities for long-term experiments could provide useful experimental settings where to critically assess how development and evolution may be interconnected. Finally, it has to be pointed out that since there are experimental data indicating a possible synergism between microgravity and space radiation, possible effects of space radiation should be taken into account in the planning and evaluation of experiments designed to test the potential role of microgravity on biological developmental and evolution.     

The radial distribution of gamma rays and cosmic rays in the outer Galaxy

The radial distribution of the high-energy (70 MeV-5 GeV) gamma-ray emissivity in the outer Milky Way is derived. The kinematics of HI are used to construct column-density maps in three galacto-centric distance ranges in the outer Galaxy. These maps are used in combination with COS-B gamma-ray data to determine gamma-ray emissivities in these distance ranges. A steep negative gradient of the emissivity for the 70 MeV-150 MeV energy range is found in the outer Galaxy. The emissivity for the 300 MeV-5 GeV range is found to be approximately constant (within 20%) and equal to the local value out to large (20 kpc) galacto-centric distances. These results imply a hardening of the gamma-ray spectrum with increrasing distance and for R > 16 kpc the spectrum is shown to be consistent with a π°-decay spectrum with the intensity expected from the local measurement of the cosmic-ray nuclei spectrum. The energy-dependent decrease is interpreted as a steep gradient in the cosmic-ray electron density and a near constancy of the nuclear component. The galactic origin of electrons with energies up to several hundreds of MeV is confirmed, while for cosmic-ray nuclei with energies of a few GeV either confinement in a large galactic halo or an extragalactic origin is suggested by the data.     

Fast spectroscopy of the 4 November 1978 gamma-ray burst

The Franco-Soviet Signe experiments on Venera 11 and Venera 12 allow a spectral analysis of gamma-ray bursts with a time resolution of 250 ms. Evidence is presented for i) short annihilation flashes of up to 20 photons cm⁻²s⁻¹ and ii) rapid variations of the continuum, from a study of the intense 4 November 1978 event.     

Spatial distribution of low energy gamma-rays associated with trapped particles

According to the data from the SONG instrument on board the low altitude high inclination CORONAS-I satellite, the fluxes of gamma rays with energies between 120 keV and 8.3 MeV are reviewed. The observations were made during the interval from May 1994 to early July 1994. Comparison with energetic electron fluxes obtained from AE-8 model is done, and thus the gamma-ray production mechanism is discussed. Available data are used to investigate the fine spatial structure in the Brazilian anomaly, as well as to analyse outer zone of bremsstrahlung electrons. To do this, the L-B maps are constructed and energy spectral characteristics of gamma-ray fluxes are investigated.     

Liquid drop model considerations in HZE particle fragmentation by hydrogen

The fragmenting of high energy, heavy ions by hydrogen targets is an important physical process in several areas of space radiation protection research. Quantum mechanical, optical model methods for calculating cross sections for particle fragmentation by hydrogen have been developed from a modified abrasion-ablation collision formalism. The abrasion stage is treated as a knockout process which leaves the residual prefragment in an excited state. In the ablation stage the prefragment deexcites to produce the final fragment. The prefragment excitation energies are estimated from a combination of liquid drop model considerations and frictional-spectator interaction processes. Estimates of elemental and isotopic production cross sections are in good agreement with published cross section measurements.     

Early development in aquatic vertebrates in near weightlessness during the D-2 Mission STATEX project.

Aboard the German-Spacelab-Mission D-2 the project "Gravity Perception and Neuronal Plasticity (STATEX II)" was performed. STATEX is for STATolith EXperiment. Objects were growing tadpoles of the South African Toad (Xenopus laevis D.) and a juvenile cichlid fish (Oreochromis mossambicus). The results give a broader base for the understanding of how environmental stimuli (e.g. linear accelerations) affect the development and function of the gravity perceiving systems in these two vertebrates. These systems are accepted as models for the human vestibulum. Results of experiments in hyper-g (up to 5 g), simulated weightlessness (Fast-rotating-clinostat) and parabolic flights are compared and discussed.