Implications of ROSAT observations for the local hot bubble

The ROSAT all-sky survey and Guest Observer pointed observations have brought a wealth of high-quality data to the study of the soft X-ray diffuse background. Analysis of the spatial structure of the 1/4 keV flux, including observations of shadows cast by discrete clouds in the interstellar medium, have allowed the separation of the observed flux into foreground and background components supporting a spatially varying local component consistent with previous ideas of the local hot bubble, a highly variable galactic halo component, and an extragalactic background.     

Similarity of the infrared spectrum of an Orgueil organic polymer with interstellar organic compounds in the line of sight towards IRS 7.

We present a comparison between the IR spectrum of the galactic center source IRS 7 and the spectrum of a carbonaceous polymer from the Orgueil meteorite. We have obtained an almost perfect match between the two spectra in the region between 3020-2790 cm-1, which suggests that the chemical composition of the interstellar organic matter and that of the meteorite polymer are similar or that the meteoritic polymer could be a well preserved interstellar organic molecule. Assuming that the meteoritic polymer has the same C/H ratio as these interstellar molecules, we find that 45 % of the total abundance of carbon in the line of sight toward IRS 7 is trapped in such an interstellar organic grain material.     

Status and future of high energy diffuse gamma-ray astronomy

There are two distinctly different high energy diffuse γ-ray components, one well correlated with broad galactic features and the other apparently isotropic and presumably extragalactic. The observed diffuse galactic high energy γ-radiation is generally thought to be produced in interactions between the cosmic rays and the interstellar matter and photons. It should then ultimately be possible to obtain from the diffuse galactic emission a detailed picture of the galactic cosmic-ray distribution, a high contrast view of the general structure of the galaxy, and further insight into molecular clouds. Two of the candidates for the explanation of the extragalactic diffuse radiation are the sum of emission from active galaxies and matter-antimatter annihilation. A major advancement in the study of the properties of both galactic and extragalactic γ radiation should occur over the next decade.     

A model of galactic cosmic rays for use in calculating linear energy transfer spectra.

The galactic cosmic rays (GCR) contain fully stripped nuclei, from Hydrogen to beyond the Iron group, accelerated to high energies and are a major component of the background radiation encountered by satellites and interplanetary spacecraft. This paper presents a GCR model which is based upon our current understanding of the astrophysics of GCR transport through interstellar and interplanetary space. The model can be used to predict the energy spectra for all stable and long-lived radioactive species from H to Ni over an energy range from 50 to 50,000 MeV/nucleon as a function of a single parameter, the solar modulation level phi. The details of this model are summarized, phi is derived for the period 1974 to present, and results from this model during the 1990/1991 CRRES mission are presented.     

Japanese satellite programs in x-ray astronomy

Future programs of x-ray astronomy in Japan are described. Following the Hakucho satellite, ASTRO-B and ASTRO-C are under preparation. $\text{ASTRO-B}$, to be launched in early 1983, is designed for the study of x-ray spectra and variability of x-ray sources. It is equipped with gas scintillation proportional counters of total area 1000 cm², one dimensional x-ray focusing collectors, transient source monitors and a gamma-ray burst monitor. $\text{ASTRO-C}$ will be launched in 1987 to study the time variability of cosmic x-ray sources with high statistical accuracies. The main emphasis is placed not only on the accurate timing analysis of the galactic sources but on the investigation of the time variability of active galactic nuclei. This satellite will be equipped with large area, low background proportional counters of total area of about 5000 cm², an all sky monitor and a gamma-ray burst detector.     

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.     

Observations of diffuse galactic positron annihilation radiation

The Galactic plane was scanned nearly three times by the UCSD/MIT Hard X-Ray and Low Energy Gamma-Ray Experiment on HEAO-1 from August 1977 through September 1978. Its Medium Energy Detectors were of the NaI/CsI phoswich type and operated over the 100 keV to 2 MeV range, with a 17° FWHM field of view and a 9% energy resolution at 511 keV. Sky maps for each epoch of observation were constructed in several energy bands. After subtraction of known point sources, a component associated with the galactic plane remains, whose spectrum is consistent with a power law and a positron annihilation spectrum. In the 333 to 583 keV energy band the flux is concentrated within ±35° of the galactic center, and the ratio of flux/radian (anticenter) is high, with a 2σ lower limit of 13. The parameters of the galactic center region's annihilation spectrum are positronium fraction of 0.9±0.1 and 511 keV flux of (2.0±0.7)×10⁻³ photons/cm²-sec-rad.     

Chemical and biological evolution in space

Astronomical infrared spectra are used to confirm the existence of complex organic molecules produced by ultraviolet photoprocessing of interstellar grain mantles. This material is shown to be the major component of the interstellar grains between the sun and the galactic center and, by inference, constitutes more than 10 million solar masses — or close to one part in a thousand of the entire mass of the milky way galaxy. It may be demonstrated that the primitive chemistry of the earth's surface was dominated by these extraterrestrial molecules after aggregated into comets if the rate of comet impacts with the earth was comparable with that required to account for the extinction of species over the past 300 million years.

Ultraviolet irradiation of bacterial spores has been studied for the first time under simulated interstellar conditions. The inactivation time predicted for the less dense regions of space is at most several hundred years. Within molecukar clouds it is shown on theoretical and experimental grounds that this t the estimated cloud. However survival of spores during their initial exposure to the solar ultraviolet presents a problem for panspermia because it requires that in the process of ejection from the earth's surface they must be enclosed within a cocoon (or mantle) of ultraviolet absorbing material of 0.6 μm thickness. Thus, although panspermia can not be rejected on the basis of lack of interstellar survival there may remain insurmountable obstacles to its occuring because of the very special protective shield requirements during ejection from its planetary source.     

Probing the galactic halo with ROSAT

We discuss the current status of ROSAT shadowing observations designed to search for emission from million degree gas in the halo of the Milky Way galaxy. Preliminary results indicate that million degree halo gas is observed in the 1/4 keV band in some directions, most notably toward the Draco cloud at (ℓ, b) = (92°, +38°), but that the halo emission is patchy and highly anisotropic. Our current understanding of this halo emission is based on a small handful of observations which have been analyzed to date. Many more observations are currently being analyzed or are scheduled for observation within the next year, and we expect our understanding of this component of the galactic halo to improve dramatically in the near future.     

Interstellar dust in the neighbourhood of the sun

The distribution of interstellar dust within 500 pc from the sun obtained from recent investigations is described. Statistical properties of dust clouds in the neighbourhood of the sun and individual data of two near clouds in high galactic latitudes are discussed. The present knowledge of the chemical composition of the interstellar dust grains is outlined. Possible relations between solar system solids and interstellar solids are indicated.     

Large scale distribution of the [CII] fine structure line in the galaxy — ISAS/UA galactic plane survey by balloon

An extensive survey of [CII] line emission has been made by using balloon borne telescopes incorporated with a liquid helium cooled Fabry-Perot spectrometer. The observations cover major part of the galactic plane in the first and fourth quadrants as well as some typical HII regions/molecular clouds complexes and a dark cloud. The observed [CII] emission is very strong and ubiquitously distributed throughout the galactic plane. The emission should be generated mostly in photo-dissociation region(PDR), but the ionizing and heating UV sources should be well mixed with the molecular clouds, presumably due to clumpy or filamentally structure of the molecular clouds. Some part of the emission may be originated from ELD HII regions which are illuminated by isolated O- and B-stars rather uniformly distributed in interstellar space.     

Clump-driven galaxy evolution and quasar activity

The collapse of a protogalaxy composed of dark matter and primordial gas has been investigated by numerical simulations and analytical multi-zone modelling in an attempt to examine the early evolution of disk galaxies. The importance of ample interstellar matter existing in young galactic disks has been highlighted. Confrontation of the theoretical results with the available observational data has led to a new picture for disk galaxy evolution, in which the bulge is the secondary object formed from disk matter. Occurrence of quasar activity is also discussed in relation to the dynamical evolution of the host galaxy.     

Exosat observations of the galactic bulge X-ray source GX17+2

We have measured the X-ray flux of the bright galactic bulge source GX17+2 in the energy range 1–20 keV using the EXOSAT ME experiment. During 8 hours of continuous observation an X-ray flare was observed (lasting ～1 hr) followed by an intensity increase. The data show intensity dips with a quasiperiod of ～1.4 hours and quasi-periodic oscillations on time scale of 200–500 sec, which are possibly connected with oscillations of an accretion disc. The spectrum can be fitted by two blackbody spectra with kT₁～1keV, and kT₂～2keV, respectively, and an iron line at 6.3 ± 0.3 keV having 130 eV equivalent width. While the low energy component is rather stable, the 2keV-component shows considerable intensity variations. We suggest that the latter component represents emission from the inner part of the accretion disc while the soft spectrum is blackbody emission from the surface of the neutron star.     

Antiparticle content in the magnetosphere

In the present work we assess the stable and transient antiparticle content of planetary magnetospheres, and subsequently we consider their capture and application to high delta-v space propulsion. We estimate the total antiparticle mass contained within the Earth’s magnetosphere to assess the expediency of such usage. Using Earth’s magnetic field region as an example, we have considered the various source mechanisms that are applicable to a planetary magnetosphere, the confinement duration versus transport processes, and the antiparticle loss mechanisms. We have estimated the content of the trapped population of antiparticles magnetically confined following production in the exosphere due to nuclear interactions between high energy cosmic rays (CR) and constituents of the residual planetary upper atmosphere.The galactic antiprotons that directly penetrate into the Earth’s magnetosphere are themselves secondary by its nature, i.e. produced in nuclear reactions of the cosmic rays passing through the interstellar matter. These antiproton fluxes are modified, dependent on energy, when penetrating into the heliosphere and subsequently into planetary magnetospheres. During its lifetime in the Galaxy, CR pass through the small grammage of the interstellar matter where they produce secondary antiprotons. In contrast to this, antiprotons generated by the same CR in magnetosphere are locally produced at a path length of several tens g/cm² of matter in the ambient planetary upper atmosphere. Due to the latter process, the resulting magnetically confined fluxes significantly exceed the fluxes of the galactic antiprotons in the Earth’s vicinity by up to two orders of magnitude at some energies.The radiation belt antiparticles can possibly be extracted with an electromagnetic-based “scoop” device. The antiparticles could be concentrated by and then stored within the superimposed magnetic field structure of such a device. In future developments, it is anticipated that the energy of the captured antiparticles (both rest energy and kinetic energy) can be adapted for use as a fuel for propelling spacecraft to high velocities for remote solar system missions.     

Globular cluster origin of X-ray bursters

X-ray bursters and galactic bulge x-ray sources, or the most luminous x-ray sources in the galaxy, are reasonably well constrained in their basic nature but not in their origin. We have suggested they may all have been produced by tidal capture in high density cores of globular clusters, which have now largely been disrupted by tidal stripping and shocking in the galactic plane. General arguments are presented for cluster disruption by the possible ring of giant molecular clouds in the Galaxy. Tests of the cluster disruption hypothesis are in progress and preliminary results are summarized here. The G-K star “companions” previously noted for at least 4 bursters have spectra (in the two cases observed) consistent with metal rich cluster giants. Several possibilities are discussed, including the formation of hierarchical triples in the dissolving cluster or in the galactic plane.     

Compact X-ray sources in nearby galaxy nuclei

We have found compact, near-nuclear X-ray sources in 21 (54%) of a complete sample of 39 nearby face-on spiral and elliptical galaxies with available ROSAT HRI data. ROSAT X-ray luminosities (0.2 – 2.4 keV) of these compact X-ray sources are ∼10³⁷ – 10⁴⁰ erg s⁻¹. The mean displacement between the location of the compact X-ray source and the optical photometric center of the galaxy is ∼390 pc. ASCA spectra of six of the 21 galaxies show the presence of a hard component with relatively steep (Γ ≈ 2.5) spectral slope. A multicolor disk blackbody plus power-law model fits the data from the spiral galaxies well, suggesting that the X-ray objects in these galaxies may be similar to a black hole candidate (BHC) in its soft (high) state. ASCA data from the elliptical galaxies indicate that hot (kT ≈ 0.7 keV) gas dominates the emission. The fact that the spectral slope of the spiral galaxy sources is steeper than in normal type 1 active galactic nuclei (AGNs) and that relatively low absorbing columns (N_H ≈ 10²¹ cm⁻²) were found to the power-law component indicates that these objects are somehow geometrically and/or physically different from AGNs in normal active galaxies. The X-ray sources in the spiral galaxies may be BHCs, low-luminosity AGNs, or possibly X-ray luminous supernovae. We estimate the black hole masses of the X-ray sources in the spiral galaxies (if they are BHCs or AGNs) to be ∼10²–10³ M_⊙. The X-ray sources in the elliptical galaxies may be BHCs, AGNs or young X-ray supernova also.     

Antideuteron based dark matter search with GAPS: Current progress and future prospects

The General Antiparticle Spectrometer (GAPS) is a new approach to the indirect detection of dark matter. It relies on searching for primary antideuterons produced in the annihilation of dark matter in the galactic halo. Low energy antideuterons produced through Standard Model processes, such as collisions of cosmic-rays with interstellar baryons, are greatly suppressed compared to primary antideuterons. Thus a low energy antideuteron search provides a clean signature of dark matter. In GAPS antiparticles are slowed down and captured in target atoms. The resultant exotic atom deexcites with the emission of X-rays and annihilation pions, protons and other particles. A tracking geometry allows for the detection of the X-rays and particles, providing a unique signature to identify the mass of the antiparticle. A prototype detector was successfully tested at the KEK accelerator in 2005, and a prototype GAPS balloon flight is scheduled for 2011. This will be followed by a full scale experiment on a long duration balloon from Antarctica in 2014. We discuss the status and future plans for GAPS.     

Development of the Infrared Telescope in Space: IRTS

Infrared Telescope in Space (IRTS) is a cryogenically cooled small infrared telescope aboard the small space platform, SFU (Space Flyer Unit). IRTS has a telescope of 15 cm diameter, which is rather small compared with other big space missions. IRTS, however, is optimized to observe extended diffuse sources with four focal plane instruments which have wide wavelength coverage from the near infrared to the submillimeter region.

All instruments have been calibrated with a test cryostat, and integrated into the flight cryostat. Cooling tests of the whole IRTS system have confirmed that instruments and cryostat will perform as expected. Integration of the IRTS on the SFU will soon begin and the ground tests of the SFU system will be conducted in the coming year.

The launch of the SFU will be in early 1995. The IRTS will survey the 10% of the sky during the three week mission and provide significant scientific results on cosmology, galactic structure, interstellar matter, stars, and solar system.     

Diffuse thermal emission from very hot gas in starburst galaxies: Spatial results

New BeppoSAX observations of the nearby prototypical starburst galaxies NGC 253 and M82 are presented. A companion paper (Cappi et al. 1998) shows that the hard (2–10 keV) spectrum of both galaxies, extracted from the source central regions, is best described by a thermal emission model with kT ∼ 6–9 keV and abundances ∼ 0.1-0.3 solar. The spatial analysis yields clear evidence that this emission is extended in NGC 253, and possibly also in M82. This quite clearly rules out a LLAGN as the main responsible for their hard X-ray emission. Significant contribution from point-sources (i.e. X-ray binaries (XRBs) and Supernovae Remnants (SNRs)) cannot be excluded; neither can we at present reliably estimate the level of Compton emission. However, we argue that such contributions shouldn't affect our main conclusion, i.e., that the BeppoSAX results show, altogether, compelling evidence for the existence of a very hot, metal-poor interstellar plasma in both galaxies.     

Mutation induction in human lymphoid cells by energetic heavy ions.

One of the concerns for extended space flight outside the magnetosphere is exposure to galactic cosmic radiation. In the series of studies presented herein, the mutagenic effectiveness of high energy heavy ions is examined using human B-lymphoblastoid cells across an LET range from 32keV/micrometer to 190 keV/micrometer. Mutations were scored for an autosomal locus, thymidine kinase (tk), and for an X-linked locus, hypoxanthine phosphoribosyltransferase (hprt). For each of the radiations studied, the autosomal locus is more sensitive to mutation induction than is the X-linked locus. When mutational yields are expressed in terms of particle fluence, the two loci respond quite differently across the range of LET. The action cross section for mutation induction peaks at 61 keV/micrometer for the tk locus and then declines for particles of higher LET, including Fe ions. For the hprt locus, the action cross section for mutation is maximal at 95 keV/micrometer but is relatively constant across the range from 61 keV/micrometer to 190 keV/micrometer. The yields of hprt-deficient mutants obtained after HZE exposure to TK6 lymphoblasts may be compared directly with published data on the induction of hprt-deficient mutants in human neonatal fibroblasts exposed to similar ions. The action cross section for induction of hprt-deficient mutants by energetic Fe ions is more than 10-fold lower for lymphoblastoid cells than for fibroblasts.