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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 631 records · Page 35
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

Magnetic diffusion effects on the ultra-high energy cosmic ray spectrum and composition

We discuss the effects of diffusion of high energy cosmic rays in turbulent extra-galactic magnetic fields. We find an approximate expression for the low energy suppression of the spectrum of the different mass components (with charge Z) in the case in which this suppression happens at energies below ∼ Z EeV, so that energy losses are dominated by the adiabatic ones. The low energy suppression appears when cosmic rays from the closest sources take a time comparable to the age of the Universe to reach the Earth. This occurs for energies E < Z EeV (B/nG)√(l{sub c}/Mpc)(d{sub s}/70Mpc) in terms of the magnetic field RMS strength B, its coherence length l{sub c} and the typical separation between sources d{sub s}. We apply this to scenarios in which the sources produce a mixed composition and have a relatively low maximum rigidity (E{sub max} ∼ (2–10)Z EeV), finding that diffusion has a significant effect on the resulting spectrum, the average mass and on its spread, in particular reducing this last one. For reasonable values of B and l{sub c} these effects can help to reproduce the composition trends observed by the Auger Collaboration for source spectra compatible with Fermi acceleration.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

The morphology of the Anomalous Microwave Emission in the Planck 2015 data release

We calculate weighted mosaic correlations between the recently published Planck 2015 foreground maps— both anomalous microwave emission (AME) maps, free-free emission, synchrotron radiation and thermal dust emission. The weighting coefficients are constructed taking account of the signal-to-error ratio given by the data product. Positive correlation is found for AME compared with thermal dust emission as well as synchrotron radiation. We find AME and free-free emission tending to be anti-correlated, however, when investigating different scales, their relationship appears to be more complex. We argue that dust particles responsible for AME are pushed out of hot zones in the interstellar medium (ISM)

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

PPPC 4 DM secondary: a Poor Particle Physicist Cookbook for secondary radiation from Dark Matter

We enlarge the set of recipes and ingredients at disposal of any poor particle physicist eager to cook up signatures from weak-scale Dark Matter models by computing two secondary emissions due to DM particles annihilating or decaying in the galactic halo, namely the radio signals from synchrotron emission and the gamma rays from bremsstrahlung. We consider several magnetic field configurations and propagation scenarios for electrons and positrons. We also provide an improved energy loss function for electrons and positrons in the Galaxy, including synchrotron losses in the different configurations, bremsstrahlung losses, ionization losses and Inverse Compton losses with an updated InterStellar Radiation Field.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Gamma-ray bounds from EAS detectors and heavy decaying dark matter constraints

The very high energy Galactic γ-ray sky is partially opaque in the (0.1–10) PeV energy range. In the light of the recently detected high energy neutrino flux by IceCube, a comparable very high energy γ-ray flux is expected in any scenario with a sizable Galactic contribution to the neutrino flux. Here we elaborate on the peculiar energy and anisotropy features imposed upon these very high energy γ-rays by the absorption on the cosmic microwave background photons and Galactic interstellar light. As a notable application of our considerations, we study the prospects of probing the PeV-scale decaying DM scenario, proposed as a possible source of IceCube neutrinos, by extensive air shower (EAS) cosmic ray experiments. In particular, we show that anisotropy measurements at EAS experiments are already sensitive to τ{sub DM}∼O(10{sup 27}) s and future measurements, using better gamma/hadron separation, can improve the limit significantly.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2015

Testing a generalized cubic Galileon gravity model with the Coma Cluster

We obtain a constraint on the parameters of a generalized cubic Galileon gravity model exhibiting the Vainshtein mechanism by using multi-wavelength observations of the Coma Cluster. The generalized cubic Galileon model is characterized by three parameters of the turning scale associated with the Vainshtein mechanism, and the amplitude of modifying a gravitational potential and a lensing potential. X-ray and Sunyaev-Zel'dovich (SZ) observations of the intra-cluster medium are sensitive to the gravitational potential, while the weak-lensing (WL) measurement is specified by the lensing potential. A joint fit of a complementary multi-wavelength dataset of X-ray, SZ and WL measurements enables us to simultaneously constrain these three parameters of the generalized cubic Galileon model for the first time. We also find a degeneracy between the cluster mass parameters and the gravitational modification parameters, which is influential in the limit of the weak screening of the fifth force.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Secondary antiprotons as a Galactic Dark Matter probe

We present a novel determination of the astrophysical uncertainties associated to the secondary antiproton flux originating from cosmic-ray spallation on the interstellar gas. We select a set of propagation models compatible with the recent B/C data from PAMELA, and find those providing minimal and maximal antiproton fluxes in different energy ranges. We use this result to determine the most conservative bounds on relevant Dark Matter (DM) annihilation channels: we find that the recent claim of a DM interpretation of a gamma-ray excess in the Galactic Center region cannot be ruled out by current antiproton data. Finally, we discuss the impact of the recently released preliminary data from AMS-02. In particular, we provide a reference model compatible with proton, helium and B/C spectra from this experiment. Remarkably, the main propagation parameters of this model are in agreement with the best fit presented in our earlier statistical analyses. We also show that the antiproton-to-proton ratio does not exhibit any significant anomaly at high energy with respect to our predictions.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Extragalactic magnetic fields unlikely generated at the electroweak phase transition

In this paper we show that magnetic fields generated at the electroweak phase transition are most likely too weak to explain the void magnetic fields apparently observed today unless they have considerable helicity. We show that, in the simplest estimates, the helicity naturally produced in conjunction with the baryon asymmetry is too small to explain observations, which require a helicity fraction at least of order 10{sup −14}–10{sup −10} depending on the void fields constraint used. Therefore new mechanisms to generate primordial helicity are required if magnetic fields generated during the electroweak phase transition should explain the extragalactic fields.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Dark matter properties implied by gamma ray interstellar emission models

We infer dark matter properties from gamma ray residuals extracted using eight different interstellar emission scenarios proposed by the Fermi-LAT Collaboration to explain the Galactic Center gamma ray excess. Adopting the most plausible simplified ansatz, we assume that the dark matter particle is a Majorana fermion interacting with standard fermions via a scalar mediator. To trivially respect flavor constraints, we only couple the mediator to third generation fermions. Using this theoretical hypothesis, and the Fermi residuals, we calculate Bayesian evidences, including Fermi-LAT exclusion limits from 15 dwarf spheroidal galaxies as well. Our evidence ratios single out one of the Fermi scenarios as most compatible with the simplified dark matter model. In this scenario the dark matter (mediator) mass is in the 25-200 (1-1000) GeV range and its annihilation is dominated by bottom quark final state. Our conclusion is that the properties of dark matter extracted from gamma ray data are highly sensitive to the modeling of the interstellar emission.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

New X-ray bound on density of primordial black holes

We set a new upper limit on the abundance of primordial black holes (PBH) based on existing X-ray data. PBH interactions with interstellar medium should result in significant fluxes of X-ray photons, which would contribute to the observed number density of compact X-ray objects in galaxies. The data constrain PBH number density in the mass range from a few M {sub ⊙} to 2× 10{sup 7} M {sub ⊙}. PBH density needed to account for the origin of black holes detected by LIGO is marginally allowed.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

ON THE POSSIBLE PRESENCE OF WEAKLY BOUND FULLERENE-H{sub 2} COMPLEXES IN THE INTERSTELLAR MEDIUM

The possible contribution of fullerenes and their derivatives to the diffuse interstellar bands (DIBs) has been discussed for some time. Bare fullerenes have been identified in the interstellar medium but they explain few, if any, of the DIBs. In this contribution we show that C{sup +}{sub 60} and C{sup +}{sub 70} will physisorb copious amounts of molecular hydrogen at low temperature. H{sub 2} forms an ordered layer around the fullerene ion; the first coordination shell closes when each carbon ring is decorated with one H{sub 2}. We estimate that fullerenes in dense clouds may very well be complexed with H{sub 2}. The occurrence of H{sub 2}-fullerene complexes in translucent clouds is less likely but cannot be ruled out. They are unlikely to occur in diffuse clouds, which are the major sources of DIBs.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2011

ORTHO-H{sub 2} AND THE AGE OF INTERSTELLAR DARK CLOUDS

Interstellar dark clouds are the sites of star formation. Their main component, dihydrogen, exists under two states, ortho and para. H{sub 2} is supposed to form in the ortho:para ratio (OPR) of 3:1 and to subsequently decay to almost pure para-H{sub 2} (OPR {<=} 0.001). Only if the H{sub 2} OPR is low enough, will deuteration enrichment, as observed in the cores of these clouds, be efficient. The second condition for strong deuteration enrichment is the local disappearance of CO, which freezes out onto grains in the core formation process. We show that this latter condition does not apply to DCO{sup +}, which, therefore, should be present all over the cloud. We find that an OPR {>=} 0.1 is necessary to prevent DCO{sup +} large-scale apparition. We conclude that the inevitable decay of ortho-H{sub 2} sets an upper limit of {approx}6 million years to the age of starless molecular clouds under usual conditions.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

CO ICE PHOTODESORPTION: A WAVELENGTH-DEPENDENT STUDY

UV-induced photodesorption of ice is a non-thermal evaporation process that can explain the presence of cold molecular gas in a range of interstellar regions. Information on the average UV photodesorption yield of astrophysically important ices exists for broadband UV lamp experiments. UV fields around low-mass pre-main-sequence stars, around shocks and in many other astrophysical environments are however often dominated by discrete atomic and molecular emission lines. It is therefore crucial to consider the wavelength dependence of photodesorption yields and mechanisms. In this work, for the first time, the wavelength-dependent photodesorption of pure CO ice is explored between 90 and 170 nm. The experiments are performed under ultra high vacuum conditions using tunable synchrotron radiation. Ice photodesorption is simultaneously probed by infrared absorption spectroscopy in reflection mode of the ice and by quadrupole mass spectrometry of the gas phase. The experimental results for CO reveal a strong wavelength dependence directly linked to the vibronic transition strengths of CO ice, implying that photodesorption is induced by electronic transition (DIET). The observed dependence on the ice absorption spectra implies relatively low photodesorption yields at 121.6 nm (Ly{alpha}), where CO barely absorbs, compared to the high yields found at wavelengths coinciding with transitions into the first electronic state of CO (A{sup 1}{Pi} at 150 nm); the CO photodesorption rates depend strongly on the UV profiles encountered in different star formation environments.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2011

ON WATER FORMATION IN THE INTERSTELLAR MEDIUM: LABORATORY STUDY OF THE O+D REACTION ON SURFACES

In the interstellar medium (ISM), an important channel of water formation is the reaction of atoms on the surface of dust grains. Here, we report on a laboratory study of the formation of water via the O+D reaction network. While prior studies were done on ices, as appropriate to the formation of water in dense clouds, we explored how water formation occurs on bare surfaces, i.e., in conditions mimicking the transition from diffuse to dense clouds (Av {approx} 1-5). Reaction products were detected during deposition and afterward when the sample is brought to a high temperature. We quantified the formation of water and intermediary products, such as D{sub 2}O{sub 2}, over a range of surface temperatures (15-25 K). The detection of OD on the surface signals the importance of this reactant in the overall scheme of water formation in the ISM.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

THE EXTREMELY HIGH VELOCITY OUTFLOW FROM THE LUMINOUS YOUNG STELLAR OBJECT G5.89-0.39

We have imaged the extremely high velocity outflowing gas in CO (2-1) and (3-2) associated with the shell-like ultracompact H II region G5.89-0.39 at a resolution of {approx}3'' (corresponding to {approx}4000 AU) with the Submillimeter Array. The integrated high-velocity ({approx}>45 km s{sup -1}) CO emission reveals at least three blueshifted lobes and two redshifted lobes. These lobes belong to two outflows, one oriented N-S, the other NW-SE. The NW-SE outflow is likely identical to the previously detected Br{gamma} outflow. Furthermore, these outflow lobes all clearly show a Hubble-like kinematic structure. For the first time, we estimate the temperature of the outflowing gas as a function of velocity with large velocity gradient calculations. Our results reveal a clear increasing trend of temperature with gas velocity. The observational features of the extremely high velocity gas associated with G5.89-0.39 qualitatively favor the jet-driven bow shock model.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

FULLERENES AND PROTO-FULLERENES IN INTERSTELLAR CARBON DUST

Laboratory spectra of hydrogenated amorphous carbon (HAC) particles prepared under a variety of conditions show spectral features at 7.05, 8.5, 17.4, and 18.9 {mu}m (1418, 1176, 575, and 529 cm{sup -1}) that have been associated with emission from C{sub 60} molecules. These lines occur in the spectra even though C{sub 60} molecules as such are not present in our samples. It appears that these four spectral lines in HAC can instead be associated with precursor molecules or 'proto-fullerenes' (PFs) that subsequently react to yield C{sub 60}. We develop a model tracing the evolution and de-hydrogenation of HAC dust and show that the observation of an emission feature at 16.4 {mu}m (610 cm{sup -1}) in astronomical spectra signals the presence of the pentagonal carbon rings required for the formation of fullerenes. We suggest that the set of four IR emission lines previously identified with C{sub 60} in many objects that also show the 16.4 {mu}m feature and other polycyclic aromatic hydrocarbon bands arise from PFs rather than C{sub 60}. Tc1 is an example of a source in which de-hydrogenation has proceeded to the point where only fullerenes are present.

36 MATERIALS SCIENCE↗
DOE OSTI2012

THE INTRACLUSTER PLASMA: A UNIVERSAL PRESSURE PROFILE?

The pressure profiles of the intracluster plasma in galaxy clusters show a wide variance when observed in X-rays at low redshifts, z {approx}< 0.2. We find the profiles to follow two main patterns, featuring either a steep or a shallow shape throughout both core and outskirts. We trace these shapes back to a physical dichotomy of clusters into two classes, marked by either low entropy (LE) or high entropy (HE) throughout. From X-ray observations and Sunyaev-Zel'dovich (SZ) stacked data at higher redshifts 0.2 {approx}< z {approx}< 0.4, we obtain evidence of an increasing abundance of HEs relative to LEs. We propose this to constitute a systematic trend toward high z; specifically, we predict the pressure profiles to converge into a truly universal HE-like template for z {approx}> 0.5. We submit our physical templates and converging trend for further observational tests, in view of current and upcoming measurements of individual, stacked, and integrated SZ signals.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

BARYON CONTENT OF MASSIVE GALAXY CLUSTERS AT z = 0-0.6

We study the relationship between two major baryonic components in galaxy clusters, namely the stars in galaxies and the ionized gas in the intracluster medium (ICM), using 94 clusters that span the redshift range 0-0.6. Accurately measured total and ICM masses from Chandra observations and stellar masses derived from the Wide-field Infrared Survey Explorer and the Two Micron All Sky Survey allow us to trace the evolution of cluster baryon content in a self-consistent fashion. We find that, within r{sub 500}, the evolution of the ICM-mass-total-mass relation is consistent with the expectation of the self-similar model, while there is no evidence for redshift evolution in the stellar-mass-total-mass relation. This suggests that the stellar mass and ICM mass in the inner parts of clusters evolve differently.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

SOFT X-RAY IRRADIATION OF PURE CARBON MONOXIDE INTERSTELLAR ICE ANALOGUES

There is an increasing evidence for the existence of large organic molecules in the interstellar and circumstellar medium. Very few among such species are readily formed in conventional gas-phase chemistry under typical conditions of interstellar clouds. Attention has therefore focused on interstellar ices as a potential source of these relatively complex species. Laboratory experiments show that irradiation of interstellar ice analogues by fast particles or ultraviolet radiation can induce significant chemical complexity. However, stars are sources of intense X-rays at almost every stage of their formation and evolution. Such radiation may thus provide chemical changes in regions where ultraviolet radiation is severely inhibited. After H{sub 2}O, CO is often the most abundant component of icy grain mantles in dense interstellar clouds and circumstellar disks. In this work we present irradiation of a pure carbon monoxide ice using a soft X-ray spectrum peaked at 0.3 keV. Analysis of irradiated samples shows formation of CO{sub 2}, C{sub 2}O, C{sub 3}O{sub 2}, C{sub 3}, C{sub 4}O, and CO{sub 3}/C{sub 5}. Comparison of X-rays and ultraviolet irradiation experiments, of the same energy dose, shows that X-rays are more efficient than ultraviolet radiation in producing new species. With the exception of CO{sub 2}, X-ray photolysis induces formation of a larger number of products with higher abundances, e.g., C{sub 3}O{sub 2} column density is about one order of magnitude higher in the X-ray experiment. To our knowledge this is the first report on X-ray photolysis of CO ices. The present results show that X-ray irradiation represents an efficient photo-chemical way to convert simple ices to more complex species.

79 ASTRONOMY AND ASTROPHYSICS↗