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Cosmic ray hazards in the solar system.
Cosmic ray hazards in solar system considered from measurements of cosmic ray energy and charge spectra near Earth and in interplanetary space near Earth, together with interaction of cosmic rays with Moon surface
Physics and astrophysics from a lunar base; Proceedings of the 1st NASA Workshop, Stanford, CA, May 19, 20, 1989
The present conference on physics and astrophysics from a lunar base encompasses space physics, cosmic ray physics, neutrino physics, experiments in gravitation and general relativity, gravitational radiation physics, cosmic background radiation, particle astrophysics, surface physics, and the physics of gamma rays and X-rays. Specific issues addressed include space-plasma physics research at a lunar base, prospects for neutral particle imaging, the atmosphere as particle detector, medium- and high-energy neutrino physics from a lunar base, muons on the moon, a search for relic supernovae antineutrinos, and the use of clocks in satellites orbiting the moon to test general relativity. Also addressed are large X-ray-detector arrays for physics experiments on the moon, and the measurement of proton decay, arcsec-source locations, halo dark matter and elemental abundances above 10 exp 15 eV at a lunar base.
THE CRAB NEBULA SUPER-FLARE IN 2011 APRIL: EXTREMELY FAST PARTICLE ACCELERATION AND GAMMA-RAY EMISSION
We report on the extremely intense and fast gamma-ray flare above 100 MeV detected by AGILE from the Crab Nebula in mid-April 2011. This event is the fourth of a sequence of reported major gamma-ray flares produced by the Crab Nebula in the period 2007/mid-2011. These events are attributed to strong radiative and plasma instabilities in the inner Crab Nebula, and their properties are crucial for theoretical studies of fast and efficient particle acceleration up to 10{sup 15} eV. Here we study the very rapid flux and spectral evolution of the event that on 2011 April 16 reached the record-high peak flux of F = (26 {+-} 5) x 10{sup -6} photons cm{sup -2} s{sup -1} with a rise-time timescale that we determine to be in the range 6-10 hr. The peak flaring gamma-ray spectrum reaches a distinct maximum near 500 MeV with no substantial emission above 1 GeV. The very rapid rise time and overall evolution of the Crab Nebula flare strongly constrain the acceleration mechanisms and challenge MHD models. We briefly discuss the theoretical implications of our observations.
Galactic cosmic ray transport methods and radiation quality issues
An overview of galactic cosmic ray (GCR) interaction and transport methods, as implemented in the Langley Research Center GCR transport code, is presented. Representative results for solar minimum, exo-magnetospheric GCR dose equivalents in water are presented on a component by component basis for various thicknesses of aluminum shielding. The impact of proposed changes to the currently used quality factors on exposure estimates and shielding requirements are quantified. Using the cellular track model of Katz, estimates of relative biological effectiveness (RBE) for the mixed GCR radiation fields are also made.
The electromagnetic radiation associated with the energy dissipated by cosmic rays in interstellar hydrogen
Electromagnetic radiation due to cosmic ray energy dissipation in interstellar hydrogen
Cosmological implication of a new measurement of the submillimeter background radiation
A new submillimeter measurement of the cosmic background radiation (T. Matsumoto et al., 1988) reveals excess brightness between 1000 and 300 microns. The excess corresponds to about 10 percent of the undistorted blackbody radiation. The observed excess is consistent with thermal emission from dust with a relative density of 0.0001-0.00001, if the dust is heated at a redshift z of about 10-40.
Progenitors of type Ia supernovae in elliptical galaxies
Although there is a nearly universal agreement that type Ia supernovae are associated with the thermonuclear disruption of a CO white dwarf, the exact nature of their progenitors is still unknown. The single degenerate scenario envisages a white dwarf accreting matter from a non-degenerate companion in a binary system. Nuclear energy of the accreted matter is released in the form of electromagnetic radiation or gives rise to numerous classical nova explosions prior to the supernova event. We show that combined X-ray output of supernova progenitors and statistics of classical novae predicted in the single degenerate scenario are inconsistent with X-ray and optical observations of nearby early type galaxies and galaxy bulges. White dwarfs accreting from a donor star in a binary system and detonating at the Chandrasekhar mass limit can account for no more than {approx}5% of type Ia supernovae observed in old stellar populations.
Transition radiation as a source of cosmic X-rays.
It is shown that transition radiation generated during the passage of relativistic charged particles through interstellar grains can be an important source of cosmic X-rays. In order to account for recent X-ray observations below 300 eV by transition radiation, an energy density in interstellar space of about 10 eV per cu cm in 10 MeV electrons is required. This seems to rule out transition radiation as an important source of diffuse cosmic X-rays in any energy region.
Natural transfer of viable microbes in space
The possibility and probability of natural transfer of viable microbes from Mars to Earth and Earth to Mars traveling in meteoroids during the first 0.5 Ga and the following 4 Ga are investigated, including: --radiation protection against the galactic cosmic ray nuclei and the solar rays, dose rates as a function of the meteorite's radial column mass (radius x density), combined with dose rates generated by natural radioactivity within the meteorite; and survival curves for some bacterial species using NASA's HZETRN transport code --other factors affecting microbe survival: vacuum; central meteorite temperatures at launch, orbiting, and arrival; pressure and acceleration at launch; spontaneous DNA decay; metal ion migration --mean sizes and numbers of unshocked meteorites ejected and percentage falling on Earth, using current semiempirical results --viable flight times for the microbe species Bacillus subtilis and Deinococcus radiodurans R1 --the approximate fraction of microbes (with properties like the two species studied) viably arriving on Earth out of those ejected from Mars during the period 4 Ga BP to the present time, and during the 700 Ma from 4.5 to 3.8 Ga. Similarly, from Earth to Mars. The conclusion is that if microbes existed or exist on Mars, viable transfer to Earth is not only possible but also highly probable, due to microbes' impressive resistance to the dangers of space transfer and to the dense traffic of billions of martian meteorites which have fallen on Earth since the dawn of our planetary system. Earth-to-Mars transfer is also possible but at a much lower frequency.
Flux and Photon Spectral Index Distributions of Fermi-LAT Blazars and Contribution to the Extragalactic Gamma-ray Background
We present a determination of the distributions of gamma-ray flux - the so called LogN-LogS relation - and photon spectral index for the 352 blazars detected with a greater than approximately seven sigma detection threshold and located above {+-} 20{sup o} Galactic latitude by the Large Area Telescope of the Fermi Gamma-ray Space Telescope in its first year catalog. Because the flux detection threshold depends on the photon index, the observed raw distributions do not provide the true LogN-LogS counts or the true distribution of the photon index. We use the non-parametric methods developed by Efron and Petrosian to reconstruct the intrinsic distributions from the observed ones which account for the data truncations introduced by observational bias and includes the effects of the possible correlation among the two variables. We demonstrate the robustness of our procedures using a simulated data set of blazars and then apply these to the real data and find that for the population as a whole the intrinsic flux distribution can be represented by a broken power law of slopes -2.37 {+-} 0.13 and -1.70 {+-} 0.26, and the intrinsic photon index distribution can be represented by a Gaussian with mean 2.41 {+-} 0.13 and 1{sigma} width of 0.25 {+-} 0.03. We also find the intrinsic distributions for the sub-populations of BL Lac and FSRQs type blazars separately. We then calculate the contribution of blazars to the diffuse cosmic gamma-ray background radiation to be 28% {+-} 19%.
Simulated Galactic Cosmic Ray and Solar Particle Event Radiation Effects on Inflatable Habitat, Composite Habitat, Space Suit and Space Hatch Cover Materials
The effect of particle radiation representative of galactic cosmic ray (GCR) and solar particle event (SPE) radiation on polymeric materials used in deep space mission environments is largely unknown. For NASA, this uncertainty represents an unquantified mission risk. To better quantify this risk, selected polymeric materials used in inflatable habitats, composite habitats, space suits and space hatch covers are irradiated at the Brookhaven National Laboratory, after which changes in relevant end-use properties are measured. The irradiated materials are lightweight candidates having critical functions such as ripstops, permeation barriers, micrometeoroids and orbital debris (MMOD) shield layers and restraint layers.The effect of several types of particle radiation are evaluated. To evaluate GCR effects, high-energy (1 GeV) protons and iron nucleons are used. To evaluate SPE effects, intermediate energy (ca. 20 to 40 MeV) protons are used. In addition, two mission scenarios are evaluated: a Mars mission cycle (space suit materials) and a worst-case 50 year deep space mission cycle (all materials). Lastly, a common polymer (high density polyethylene (HDPE)) is subjected to accelerated aging and radiation exposure to determine if a combined physical aging/radiation effect exists.The level of radiation induced property change observed in this study after exposure of polymers to kGy levels of intermediate and high energy ions is often significant and is quantitatively comparable to the level of change reported for similar materials exposed to MGy levels of low energy protons, electrons and gamma-radiation. This suggests that intermediate and high energy ions encountered in space may cause more damage than low energy forms of radiation due to displacement and linear energy transfer (LET) effects. For these reasons, it is recommended that final approval for mission use be made by the appropriate NASA material and structural review boards to ensure radiation induced changes in candidate materials do not interfere with their engineering function in the intended mission application. Since the materials tested in this report received doses exceeding actual mission doses, the results are considered conservative as a first approximation. However, caution must be exercised when evaluating radiation effects in the absence of other secondary factors know to contribute to degradation. In the addition to radiation type and energy, the results presented in this study show that molecular composition, orientation, stress and physical aging can also contribute to or influence degradation. Other factors such as polymer formulation, secondary radiation effects, stress, exposure to elevated temperature, thermal cycling and exposure to ozone were not investigated here, but must be considered when performing a comprehensive evaluation of a polymeric materials suitability for service in a space radiation environment. Only when the total sum of these factors operating in concert with radiation are accounted for, can accurate assessments of a material's suitability be made.
A PHOTOMETRIC REDSHIFT OF z {approx} 9.4 FOR GRB 090429B
Gamma-ray bursts (GRBs) serve as powerful probes of the early universe, with their luminous afterglows revealing the locations and physical properties of star-forming galaxies at the highest redshifts, and potentially locating first-generation (Population III) stars. Since GRB afterglows have intrinsically very simple spectra, they allow robust redshifts from low signal-to-noise spectroscopy, or photometry. Here we present a photometric redshift of z {approx} 9.4 for the Swift detected GRB 090429B based on deep observations with Gemini-North, the Very Large Telescope, and the GRB Optical and Near-infrared Detector. Assuming a Small Magellanic Cloud dust law (which has been found in a majority of GRB sight lines), the 90% likelihood range for the redshift is 9.06 < z < 9.52, although there is a low-probability tail toward somewhat lower redshifts. Adopting Milky Way or Large Magellanic Cloud dust laws leads to very similar conclusions, while a Maiolino law does allow somewhat lower redshift solutions, though in all cases the most likely redshift is found to be z > 7. The non-detection of the host galaxy to deep limits (Y(AB) {approx} 28, which would correspond roughly to 0.001L* at z = 1) in our late-time optical and infrared observations with the Hubble Space Telescope strongly supports the extreme-redshift origin of GRB 090429B, since we would expect to have detected any low-z galaxy, even if it were highly dusty. Finally, the energetics of GRB 090429B are comparable to those of other GRBs and suggest that its progenitor is not greatly different from those of lower redshift bursts.
QSO's to B less than 22 and the cosmic x ray background radiation: A fluctuations correlation approach
The contribution of faint Quasi Stellar Objects (QSO's) and other discrete sources to the cosmic X-Ray Background (XRB) is estimated using an optically selected QSO sample in SA 68.2 in conjunction with archived x-ray images from the Einstein Image Proportional Counter (IPC). A new generalization of the 'x-ray image stacking' technique is employed; this new approach tests for a positional 'correlation' between positive x-ray fluctuations in the IPC images, and the locations of the optically selected QSO's. Correlation with thirty SA 68.2 QSO's permits a highly sensitive measurement of the ensemble mean x-ray flux for QSO's with 19 less than B(sub J) less than 22. Although the IPC images are of modest depth, a limiting sensitivity 1.2 times 10 to the minus 14th power erg/sec/sq cm (0.3 to 3.5 keV) is effectively archieved comparable to that of the Rosat medium deep surveys.
REPLY TO THE DISCUSSION BY W. N. HESS
Increased intensity of inner radiation belt, cosmic rays, atmospheric density, trapped particle
IMPLICATIONS OF UNDERSTANDING SHORT GAMMA-RAY BURSTS DETECTED BY SWIFT
In an effort to understand the puzzle of classifying gamma-ray bursts (GRBs), we perform a systematic study of Swift GRBs and investigate several short GRB issues. Though short GRBs have a short ({approx}< 2 s) prompt duration as monitored by the Burst Alert Telescope, the composite light curves including both the prompt and afterglow emission suggest that most of the short GRBs have a similar radiative feature to long GRBs. Furthermore, some well-studied short GRBs might also have an intrinsically long prompt duration, which renders them as a type of short GRB imposters. Genuine short GRBs detected by Swift might be rare, so determining the observed short GRBs is, not surprisingly, troublesome. In particular, the observational biases in the host identification and redshift measurement of GRBs should be taken with great caution. The redshift distribution, which has been found to be different for long and short GRBs, might have been strongly affected by the measurement methods. We find that the redshifts measured from the presumed host galaxies of long and short GRBs appear to have a similar distribution.
On Influence of Neutrals on Dust Particle Charging in Complex Plasmas in the Presence of Electromagnetic Radiation
Effects associated with neutral component of complex (dusty) ionospheric plasmas which affect dust particle charging are studied. Microscopic ion currents on dust particles with taking into account ion-neutral interaction are presented. Calculations are performed both for the case of negative charges of dust particles, when the influence of Solar radiation on dust particle charging processes is negligible, and for the case of positive charges which is realized in the presence of sufficiently intensive UV or X-ray radiation. We also carry out investigation of the electron heating due to the photoelectric effect. We show that the efficiency of electron heating depends on the density of neutral component of the plasma. As result, we determine altitudes where the influence of the neutral plasma component on dust particle charging processes as well as the electron heating effect are significant and should be taken into account under consideration of the ionospheric complex plasmas. In particular, we show that the effects considered could be important for the description of noctilucent clouds, polar mesosphere summer echoes, and some other physical phenomena associated with dust particles in the ionosphere.
NASA’s Galactic Cosmic Ray Simulator – How we study the effects of space radiation on Earth
Earth’s atmosphere and natural magnetic field do a good job protecting us from space radiation. Space radiation is different from radiation on Earth, which mostly comes from isotopes found in rock and soil or from medical procedures like an Xray. Ionizing space radiation comes from particles ejected from the Sun, or solar particle events, and from supernovae outside our solar system making up a background of galactic cosmic radiation. These particles, representing the elements of the periodic table, have been stripped of their electrons as they are accelerated in interstellar space to almost the speed of light. One of NASA’s biggest challenges is protecting astronauts from these high energy particles of galactic cosmic radiation which can cause cancer and other diseases. To understand the biological damage imparted to living systems and to develop protective countermeasures, NASA has built a galactic cosmic ray simulator on Earth.