Gamma ray astrophysics and signatures of axion-like particles

We propose that axion-like particles (ALPs) with a two-photon vertex, consistent with all astrophysical and laboratory bounds, may lead to effects in the spectra of high-energy gamma-ray sources detectable by satellite or ground-based telescopes. We discuss two kinds of signatures: (i) a peculiar spectral depletion due to gamma rays being converted into ALPs in the magnetic fields of efficient astrophysical accelerators according to the “Hillas criterion”, such as jets of active galactic nuclei or hot spots of radio galaxies; (ii) an appearance of otherwise invisible sources in the GeV or TeV sky due to back-conversion of an ALP flux (associated with gamma-ray emitters suffering some attenuation) in the magnetic field of the Milky Way. These two mechanisms might also provide an exotic way to avoid the exponential cutoff of very high energy gamma-rays expected due to the pair production onto the extragalactic background light.     

Testing the no-hair theorem with observations of black holes in the electromagnetic spectrum

According to the no-hair theorem, astrophysical black holes are uniquely described by their mass and spin. In this paper, we review a new framework for testing the no-hair hypothesis with observations in the electromagnetic spectrum. The approach is formulated in terms of a Kerr-like spacetime containing a quadrupole moment that is independent of both mass and spin. If the no-hair theorem is correct, then any deviation from the Kerr metric quadrupole has to be zero. We show how upcoming VLBI imaging observations of Sgr A∗ as well as spectroscopic observations of iron lines from accreting black holes with IXO may lead to the first astrophysical test of the no-hair theorem.     

Three-dimensional magnetic reconnection regimes: A review

The magnetic field in many astrophysical plasmas – such as the solar corona and Earth’s magnetosphere – has been shown to have a highly complex, three-dimensional structure. Recent advances in theory and computational simulations have shown that reconnection in these fields also has a three-dimensional nature, in contrast to the widely used two-dimensional (or 2.5-dimensional) models. Here we discuss the underlying theory of three-dimensional magnetic reconnection. We also review a selection of new models that illustrate the current state of the art, as well as highlighting the complexity of energy release processes mediated by reconnection in complicated three-dimensional magnetic fields.     

MHD simulations and astrophysical applications

Magnetohydrodynamics is an adequate theoretical framework to study a large variety of astrophysical flows. The generation of magnetic fields by dynamo mechanisms, the development of turbulent flows or the topological change of magnetic fields by reconnection, are just a few examples. First, we describe the basic features of the MHD framework. Second, we make a brief introduction to the physical processes listed above, namely: dynamo action, MHD turbulence, and magnetic reconnection. Finally, we show the results arising from numerical simulations of these processes, for a number of configurations of astrophysical interest.     

XANES analysis of organic residues produced from the UV irradiation of astrophysical ice analogs

Organic residues formed in the laboratory from the ultraviolet (UV) photo-irradiation or ion bombardment of astrophysical ice analogs have been extensively studied for the last 15 years with a broad suite of techniques, including infrared (IR) and UV spectroscopies, as well as mass spectrometry. Analyses of these materials show that they consist of complex mixtures of organic compounds stable at room temperature, mostly soluble, that have not been fully characterized. However, the hydrolysis products of these residues have been partly identified using chromatography techniques, which indicate that they contain molecular precursors of prebiotic interest such as amino acids, nitrile-bearing compounds, and amphiphilic compounds. In this study, we present the first X-ray absorption near-edge structure (XANES) spectroscopy measurements of three organic residues made from the UV irradiation of ices having different starting compositions. XANES spectra confirm the presence of different chemical functions in these residues, and indicate that they are rich in nitrogen- and oxygen-bearing species. These data can be compared with XANES measurements of extraterrestrial materials. Finally, this study also shows how soft X rays can alter the chemical composition of samples.     

The gas pixel detector as a solar X-ray polarimeter and imager

The Sun is the nearest astrophysical source with a very intense emission in the X-ray band. The study of energetic events, such as solar flares, can help us to understand the behaviour of the magnetic field of our star. There are in the literature numerous studies published about polarization predictions, for a wide range of solar flares models involving the emission from thermal and/or non-thermal processes, but observations in the X-ray band have never been exhaustive.The gas pixel detector (GPD) was designed to achieve X-ray polarimetric measurements as well as X-ray images for far astrophysical sources. Here we present the possibility to employ this instrument for the observation of our Sun in the X-ray band.     

Study of fast atoms in molecular gas plasma via emission spectroscopy

Fast atoms are generated in reactions of ions with the molecular gas in laboratory and astrophysical plasma. In hydrogen they are observed in the emission spectra via Excessive line broadening. Energetic atoms also occur in astrophysical plasma in hydrogen, nitrogen and oxygen. The proposal here is that low pressure discharges can be used to simulate the phenomena in certain space plasma. In this study, we have used a special configuration of the electrode system, to obtain energetic atoms in plasma of three types of diatomic gases (H₂, O₂, N₂). Emission spectroscopy was used to detect the atoms and measure their velocity. Energy analysis was performed to obtain atoms’ distributions and evaluate the mean energy of atoms. This was compared to the potential energy available from the electric field. The field acceleration model, previously established for hydrogen, was extended to nitrogen and oxygen. We suggest, that the same method of analysis can be applied for astrophysical plasma spectrum.     

Dynamics of stellar systems: Violent relaxation and gravothermal catastrophe

The gravitational evolution of stellar systems exhibit collective and collisional effects. Collective effects (Violent Relaxation) seems to be unefficient to create any structure or to relax the distribution function. Gravothermal Catastrophe is shown to be a real instability driven by collisions, but its time scale is very long compared to astrophysical times. It is suggested that intermediate range perturbations may modify these conclusions.     

Status and perspectives of indirect and direct dark matter searches

In this review article the current status of particle dark matter is addressed. We discuss the main theoretical extensions of the standard model which allow to explain dark matter in terms of a (yet undiscovered) elementary particle. We then discuss the theoretical predictions for the searches of particle dark matter: direct detection in low-background underground experiments and indirect detection of neutrinos, gamma-rays and antimatter with terrestrial and space-borne detectors. Attention will be placed also on the discussion of the uncertainties, mainly of astrophysical origin, which affect the theoretical predictions. The constraints placed by these searches on the extensions of the standard models will be briefly addressed.     

Local stability analysis of interface region of astrophysical viscous shear flows with a gradual velocity gradient

In this paper, we extend the stability analysis of cold sharp shear flows to warm astrophysical cases with, inevitable, gradual velocity gradient in the interface region in the presence of viscosity effect. Using linear perturbation theory as well as the local approximation method, the instability growth rate of the excited electromagnetic modes has been investigated for the relativistic and non-relativistic cases of solar wind interacting with interstellar plasma medium. Results show that astrophysical shear systems with a small velocity gradient in the transition region are more stable rather than larger ones. Moreover, dependent on the viscosity coefficient value, the viscosity effects could have a positive role on the instability growth rate of the system in some range of initial bulk velocity, while it plays a destructive role in other velocity ranges.     

Infrared observations of contaminants from shuttle flight 51-F

A small helium cooled infrared telescope, IRT, was flown on the Shuttle in July/August 1985. The principle astrophysical objectives were to measure the large scale structure of sources and the background radiation. A cold shutter was incorporated to permit absolute flux measurements. Additionally, the engineering objectives included setting upper limits on the infrared radiation from the local environment. Even though the local background overwhelmed the astrophysical background, astronomical sources were still detectable superimposed on this background radiation. Data are presented covering the spectral range from 2μm to 120μm. The spatial, spectral and temporal variations are described. Based on the spectral character and variability in different wavelength bands, the background radiation does not appear to have a single origin. In this paper the results on the Shuttle environment will be presented. The astrophysical results will be presented elsewhere.     

MultiWaveLink: An interactive data base for the coordination of multiwavelength and multifacility observations

MultiWaveLink is an interactive, computerized data base that was developed to facilitate a multiwavelength approach to studying astrophysical sources. It can be used to access information about multiwavelength resources (observers, telescopes, data bases and analysis facilities) or to organize observing campaigns that require either many telescopes operating in different spectral regimes or a network of similar telescopes circumspanning the Earth.     

Limits of photosynthesis in extrasolar planetary systems for earth-like planets.

We present a general modeling scheme for investigating the possibility of photosynthesis-based life on extrasolar planets. The scheme focuses on the identification of the habitable zone in main-sequence-star planetary systems with planets of Earth mass and size. Our definition of habitability is based on the long-term possibility of photosynthetic biomass production as a function of mean planetary surface temperature and atmospheric CO2-content. All the astrophysical, climatological, biogeochemical, and geodynamic key processes involved in the generation of photosynthesis-driven life conditions are taken into account. Implicitly, a co-genetic origin of the central star and the orbiting planet is assumed. The numerical solution of an advanced geodynamic model yields realistic look-up diagrams for determining the limits of photosynthesis in extrasolar planetary systems, assuming minimum CO2 levels set by the demand of C4 photosynthesis.     

Radiation-induced apoptosis in scid mice spleen after low dose irradiation.

To assess the radioadaptive response of the whole body system in mice, we examined the temporal effect of low dose priming as an indicator of challenging irradiation-induced apoptosis through a p53 tumor suppressor protein- mediated signal transduction pathway. The p53 protein also plays an important role both in cell cycle control and DNA repair through cellular signal transduction. Using severe combined immunodeficiency mice defective in DNA-dependent protein kinase catalytic subunit, we examined the role of DNA-dependent protein kinase activity in radioadaptation induced by low dose irradiation. Specific pathogen free 5-week-old female severe combined immunodeficiency mice and the parental mice (CB- 17 Icr +/+) were irradiated with X-ray at 3.0 Gy at 1, 2, 3 or 4 weeks after the conditioning irradiation at 0.15, 0.30, 0.45 or 0.60 Gy. The mice spleens were fixed for immunohistochemistry 12 h after the challenging irradiation. The p53-dependent apoptosis related Bax proteins on formalin-fixed paraffin-embedded sections were stained by the avidin-biotin peroxidase complex method. The apoptosis incidence in the sections was measured by hematoxylin-eosin staining. The frequency of Bax- and apoptosis-positive cells increased up to 12 h after the challenging irradiation in the spleen of both mice. However, these cells were not observed after a low dose irradiation at 0.15-0.60 Gy. When pre-irradiation at 0.45 Gy 2 weeks before the challenging irradiation at 3.0 Gy was performed, Bax accumulation and apoptosis induced by challenging irradiation were depressed in the spleens of CB-17 Icr +/+ mice, but not in severe combined immunodeficiency mice. These data suggest that DNA-dependent protein kinase might play a major role in radioadaptation induced by pre-irradiation with a low dose in mice spleen. We expect that the present findings will provide useful information in the health care of space crews.     

From the interstellar clouds, through the inner to the outer solar system: a universally distributed complex organic chemistry. Preface.

High molecular weight organic compounds are involved in the chemistry and physics of many astrophysical and planetary objects. They are or should be present in interstellar dust, in comets and meteorites, in the Giant planets and Titan, in asteroids Triton and icy satellites. They represent a class of very complex organic material, part of which may have played a role in the origin of life on Earth. Thus they directly concern prebiotic chemistry and exobiology.     

GRB 980425, SN1998BW and the EMBH model

The EMBH model, previously developed using GRB 991216 as a prototype, is here applied to GRB 980425. We fit the luminosity observed in the 40–700 keV, 2–26 keV and 2–10 keV bands by the BeppoSAX satellite. In addition we present a novel scenario in which the supernova SN1998bw is the outcome of an “induced gravitational collapse” triggered by GRB 980425, in agreement with the GRB-Supernova Time Sequence (GSTS) paradigm [Ruffini, R., Bianco, C.L., Chardonnet, P., Fraschetti, F., Xue, S.-S. On a possible GRB-supernova time sequence. Astrophys. J. 555, L117–L120, 2001c]. A further outcome of this astrophysically exceptional sequence of events is the formation of a young neutron star generated by the SN1998bw event. A coordinated observational activity is recommended to further enlighten the underlying scenario of this most unique astrophysical system.     

Detection of microlesions induced by heavy ions using liposomes filled with fluorescent dye.

In cells irradiation by heavy ions has been hypothesized to produce microlesions, regions of local damage. In cell membranes this damage is thought to manifest itself in the form of holes. The primary evidence for microlesions comes from morphological studies of cell membranes, but this evidence is still controversial, especially since holes also have been observed in membranes of normal, nonirradiated, cells. However, it is possible that damage not associated with histologically discernable disruptions may still occur. In order to resolve this issue, we developed a system for detecting microlesions based on liposomes filled with fluorescent dye. We hypothesized that if microlesions form in these liposomes as the result of irradiation, then the entrapped dye will leak out into the surrounding medium in a measurable way. Polypropylene vials containing suspensions of vesicles composed of either dipalmitoyl phosphatidylcholine, or a combination of egg phosphatidylcholine and cholesterol were irradiated at the Brookhaven National Laboratory using 56Fe ions at 1 GeV/amu. In several cases we obtained a significant loss of the entrapped dye above the background level. Our results suggest that holes may form in liposomes as the result of heavy ion irradiation, and that these holes are large enough to allow leakage of cell internal contents that are at least as large as a 1 nm diameter calcein molecule.     

Organic solids produced from simple C/H/O/N ices by charged particles: applications to the outer solar system.

CH4, CO, and CO2 are all potential one-carbon molecular repositories in primitive icy objects. These molecules are all found in the Comet Halley coma, and are probable but, (except for CH4 detected on Triton and Pluto) undetected subsurface constituents in icy outer solar system objects. We have investigated the effects of charged particle irradiation by cold plasma discharge upon surfaces of H2O:CH4 clathrate having a 200:1 ratio, as well as upon ices composed of H2O plus C2H6 or C2H2 (sometimes plus NH3) which are also plausible constituents. These materials color and darken noticeably after a dose 10(9) - 10(10) erg cm-2, which is deposited rapidly (< or = 10(4) yr.) in solar system environments. The chromophore is a yellowish to tan organic material (a tholin) which we have studied by UV-VIS reflection and transmission, and IR transmission spectroscopy. Its yield, -1 C keV-1, implies substantial production of organic solids by the action of cosmic rays and radionuclides in cometary crusts and interiors, as well as rapid production in satellite surfaces. This material shows alkane bands which Chyba and Sagan have shown to well match the Halley infrared emission spectrum near 3.4 microns, and also bands due to aldehyde, alcohol and perhaps alkene/aromatic functional groups. We compare the IR spectral properties of these tholins with the spectra of others produced by irradiation of gases and ices containing simple hydrocarbons.