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NASA NTRS2003

RGS Spectroscopy of the Cygnus Loop XA Knot

The observations were performed at the end of April 2002, and the data were received in July 2002. Unfortunately, the observations were badly compromised by high levels of background radiation; one the three observations lost entirely. Two replacement observations were scheduled for November 2002, and were only made available in January of 2003. Consequently, we have had little time to grapple with the unusual data analysis challenges. The search for a postdoctoral fellow has been successfully concluded, and Manami Sasaki began working for us in January 2003. She will be supported in part by these funds, and will be working to help understand these data. Examination of the RGS 'Orders' images indicate the presence of broad emission lines (as expected for the diffuse XA knot). However, examination of the 'Spatial' dispersion/cross-dispersion images indicate that the emission is also broad in the cross-dispersion direction. (As a crosscheck, some of the 'Lockman Hole' datasets were also examined as representative 'sky background' datasets; in these, both types of images are relatively flat (outside the calibration source regions). The quicklook plots of the spectra show the expected O VII and O VIII lines, in addition to a complex around 35 Angstroms; the approx. 35 Angstrom line is likely the C V He-beta line at 34.97 Angstrom, but identifying the additional line(s) will require a more careful reduction of the data. Consequently, there is valuable information to be extracted from these data, but it is complicated by diffuse nature of the emission. Because the angular scale is large, we will have to make use of sky background datasets in order to do the background fitting. A color composite image of OM data in the three UV bands was presented at the 'How does the Galaxy Work?' meeting, and compared to optical and X-ray imaging data. Quantitative analysis will require obtaining the effective bandpasses of the UV filters so that the predominant line and continuum contributions can be identified using plasma shock emission models. In view of the facts that the data were only obtained relatively recently, and the complexity of the data analysis, we request a one year no-cost extension on the grant.

Gaetz, Terrance J.↗
NASA NTRS2002

Cometary Silicates: Interstellar and Nebular Materials

Evidence for interstellar material in comets is deduced from IR spectra, insitu measurements of Halley, and chondritic porous interplanetary dust particles (CP IDPs). IR spectra of comets reveal the spectrally active minerals: amorphous carbon, amorphous silicates, and (in some comets) crystalline silicates. Evidence suggests amorphous silicates are of interstellar origin while crystalline silicates are of nebular origin. 10 microns spectra of comets and submicron amorphous silicate spherules in CP IDPs have shapes similar to lines-of-sight through the ISM. Thermal emission models of cometary IR spectra require Fe-bearing amorphous silicates. Fe-bearing amorphous silicates may be Fe-bearing crystalline silicates formed in AGB outflows that are amorphized through He+ ion bombardment in supernova shocks in the ISM. Crystalline silicates in comets, as revealed by IR spectra, and their apparent absence in the ISM, argues for their nebular origin. The high temperatures (less than l000 K) at which crystals form or are annealed occur in the inner nebula or in nebular shocks in the 5-10 AU region. Oxygen isotope studies of CP IDPs show by mass only 1 % of the silicate crystals are of AGB origin. Together this suggests crystalline silicates in comets are probably primitive grains from the early solar nebula.

Wooden, Diane H.↗
NASA NTRS2002

Disappearance of 19P/Borrelly's Silicate Feature in 2001 Apparition Is Attributed to Increase in Grain Size

We report on observations and analysis of HIFOGS 10 microns spectrophotometry of short period comet 19P/Borrelly on 2003 October 13, 15 UT at the NASA IRTF. 19P/Borrelly is one of two short period comets, comet 4PIFaye being the other, to have a silicate feature detected. During Borrelly s perihelion passage in 1994 December, a silicate feature was present with a flux-to-continuum ratio of 0.25. Two apparitions later in 2003 October, the silicate feature is absent. Thermal emission modeling using amorphous olivine and amorphous carbon shows that a slight increase in grain size accounts for the disappearance of the silicate feature. Analysis of 19P/Borrelly suggests grain size, and not the absence of olivine minerals, may be responsible for the absence of silicate features in most short period comets. 19P/Borrelly is one of the more active short period comets. However, short period comets as a family are less active than long period comets. Short period comets probably originated in the Kuiper Belt and suffered collisions while in residence in the outer solar system. Upon evolution into orbits that take them through the inner solar system, the surfaces of short period comets are exposed to sunlight through their many perihelion passages. This is in contrast to long period comets which probably originated near Jupiter and were expelled to the Oort cloud where they have existed and been exposed to cosmic ray processing. By studying the grain properties in short period comets and comparing to long period comets, we compare the effects on the grain populations of different parent body evolution histories. Upcoming opportunities to study short and long period comets will be advertised.

Wooden, D. H.↗
NASA NTRS2004

High Energy Astrophysics Tests of Lorentz Invariance Violation

Observations of the multi-TeV spectra of the Mkn 501 and other nearby BL Lac objects exhibit the high energy cutoffs predicted to be the result of intergalactic annihilation interactions, primarily with IR photons having a flux level as determined by various astronomical observations. After correcting for such intergalactic absorption, these spectra can be explained within the framework of synchrotron self-Compton emission models. Stecker and Glashow have shown that the existence of this annihilation via electron-positron pair production puts strong constraints on Lorentz invariance violation. Such constraints have important implications for some quantum gravity and large extra dimension models. A much smaller amount of Lorentz invariance violation has potential implications for understanding the spectra of ultrahigh energy cosmic rays.

Stecker, F. W.↗
NASA NTRS2004

High Energy Astrophysics Tests of Lorentz Invariance Violation

Observations of the multi-TeV spectra of the nearby BL Lac objects Mkn 421 and Mkn 501 exhibit the high energy cutoffs predicted to be the result of intergalactic annihilation interactions, primarily with IR photons having a flux level as determined by various astronomical observations. After correcting for such intergalactic absorption, these spectra can be explained within the framework of synchrotron self-Compton emission models. Stecker & Glashow have shown that the existence of this annihilation via electron-positron pair production puts strong constraints on Lorentz violation. We will show that such constraints have important implications for some quantum gravity models and large extra dimension models. We will also discuss the potentially important effects of a smaller Lorentz violation which is consistent with these constraints on the propagation and spectra of ultrahigh energy cosmic rays.

Stecker, Floyd W.↗
NASA NTRS2004

High Silicate Crystalline-to-Amorphous Ratios in Comets C/2001 Q4 (NEAT) and Hale-Bopp

Crystalline silicates, by their apparent absence in the ISM, are dust grains that experienced high temperatures in the solar nebula. Mg-rich crystalline silicates formed either by condensation from hot nebular gases (1450 K) or by the annealing of Mg-rich amorphous silicates (approx. 1000 K) in shocks in the 5-10 AU region or by radial transport into and out of the hot inner zones, e.g., T(sub d) > 1000 K at r(sub h) < 5 AU, 10(exp -6) - 10(exp -5) M(sub O)/yr, alpha = 10(exp -4) of the early solar nebula. Mg-rich crystalline silicates are found in interplanetary dust particles (IDPs) and produce IR spectral features in many Oort cloud comets. In May 2004, we discovered strong crystalline silicate features in the dynamically new Oort cloud comet C/2001 Q4 (NEAT). Thermal emission modeling of comets Q4 and C/1995 O1 (Hale-Bopp) demonstrate that both these comets have similar, high silicate crystalline-to-amorphous ratios of 2.4 and 2.1, respectively, indicating that these icy planetesimals aggregated from similar reservoirs of material or that crystalline silicates were widely distributed within the comet-forming zone. This argues for efficient annealing mechanisms and radial mixing.

Wooden, D. H.↗
NASA NTRS2004

High Silicate Crystalline-to-Amorphous Ratios in Comets C/2001 Q4 (NEAT) and Hale-Bopp

Crystalline silicates, by their apparent absence in the ISM, are dust grains that experienced high temperatures in the solar nebula. Mg-rich crystalline silicates formed either by condensation from hot nebular gases (1450 K) or by the annealing of Mg-rich amorphous silicates (approximately 1000 K) in shocks in the 5-10AU region or by radial transport into and out of the hot inner zones, e.g., T(sub d) greater than 1000K at r(sub h) less than 5AU, 10(exp -6) -10(exp -5) solar mass per year, alpha = 10(exp -4) of the early solar nebula. Mg-rich crystalline silicates are found in interplanetary dust particles (IDPs) and produce IR spectral features in many Oort cloud comets. In May 2004, we discovered strong crystalline silicate features in the dynamically new Oort cloud comet C/2001 Q4 (NEAT). Thermal emission modeling of comets Q4 and C/1995 O1 (Hale-Bopp) demonstrate that both these comets have similar, high silicate crystalline-toamorphous ratios of 2.4 and 2.1, respectively, indicating that these icy planetesimals aggregated from similar reservoirs of material or that crystalline silicates were widely distributed within the comet-forming zone. This argues for efficient annealing mechanisms and radial mixing.

Wooden, D. H.↗
NASA NTRS2006

Confirmation of the E(sup src)(sub Peak)-E(sub iso) (Amati) relation from the x-ray flash XRF 050416A observed by the Swift burst alert telescope

We report Swift Burst Alert Telescope (BAT) observations of the X-ray flash (XRF) XRF 050416A. The fluence ratio between the 15-25 and 25-50 keV energy bands of this event is 1.5, thus making it the softest gamma-ray burst (GRB) observed by BAT so far. The spectrum is well fitted by a Band function with E(sup obs)(sub peak) of 15.0(sup +2.3)(sub -2.7) keV. Assuming the redshift of the host galaxy (z = 0.6535), the isotropic equivalent radiated energy E(sub iso) and the peak energy at the GRB rest frame (E(sup src)(sub peak)) of XRF 050416A are not only consistent with the correlation found by Amati et al. and extended to XRFs by Sakamoto et al. but also fill in the gap of this relation around the 30-80 keV range of E(sup src)(sub peak). This result tightens the validity of the E(sup src)(sub Peak)-E(sup src)(sub peak) relation from XRFs to GRBs. We also find that the jet break time estimated using the empirical relation between E(sup src)(sub peak) and the collimation corrected energy E(sub gamma), is inconsistent with the afterglow observation by the Swift X-Ray Telescope. This could be due to the extra external shock emission overlaid around the jet break time or to the nonexistence of a jet break feature for XRFs, which might be a further challenge for GRB jet emission models and XRF/GRB unification scenarios.

Sakamoti, T.↗
NASA NTRS1993

Polarimetric Passive Remote Sensing of Wind-generated Sea Surfaces and Ocean Wind Vectors

This paper investigates the theory of polarimetric passive remote sensing of wind-generated sea surfaces. A two-scale polarimetric scattering and emission model of sea surfaces is developed to interpret existing active and passive remote sensing microwave signatures of sea surfaces, and to investigate the potential application of polarimetic radiometry to ocean surface winds.

Polarimetric Remote Sensing↗
NASA NTRS2006

Comet Mineralogy as Inferred from Infrared Spectra of Comets

For most comets, infrared (IR) spectroscopy (remote sensing) is the method through which we diagnose the mineralogy and size distribution of dust in their comae. The shape and contrast of the IR spectral features depend on the particle size: optically active minerals (absorbing of visible and near-IR solar photons) and submicron solid grains or highly porous (> 90% vacuum) grains primarily contribute to the shapes of the observed resonances. Comet mineralogies typically are determined by fitting thermal emission models of ensembles of discrete mineral grains to observed IR spectral energy distributions. The absorptivities (Q-abs) and scattering efficiencies (Q-scat) of the discrete mineral grains are computed using Mie scattering, Maxwell-Garnet mixing, Discrete Dipole Approximation, and Multi-Layered Sphere codes. These techniques when applied to crystalline minerals, specifically olivine (Mg_x, Fe_1-x)2 Si04, x>0.9, require the use of ellipsoidal shaped particles with elongated axial ratios or hollow spheres to produce the shapes of the resonances observed both from comet comae and laboratory samples. The wavelength positions of the distinct resonances from submicron-radii crystalline silicates, as well as their thermal equilibrium temperatures, constrain the crystalline olivine to have a relatively high Mg-content (x>0.9, or Fo>90). Only resonances computed for submicron Mg-rich crystalline olivine and crystalline orthopyroxene match the observed IR spectral features. However, this has led to the interpretation that micron-radii and larger crystals are absent from comet comae. Furthermore, the mass fraction of silicate crystals is dependent upon whether just the submicron portion of the size distribution is being compared or the submicron crystals compare to the aggregates of porous amorphous silicates that are computationally tractable as porous spheres. We will discuss the Deep Impact results as examples of these challenges to interpreting mid-IR spectra of short-period comets.

Wooden, Diane H.↗
NASA NTRS2004

Observing NGC 4151 with the Keck Interferometer

Observations of the nucleus of NGC 4151 at 2.2 microns using the two 10-meter Keck telescopes as an interferometer show a marginally resolved source less than or equal to 0.1 pc in diameter. These observations are the first measurement of an extragalactic source with an optical/IR interferometer. These observations represent a ten-fold improvement in angular resolution when compared to previous near-infrared measurements of AGN and make it possible to test the subparsecscale, near-infrared emission models of NGC 4151.

interferometry↗
NASA NTRS2010

Spitzer Observations of Dust Destruction in the Puppis A Supernova Remnant

Imaging and spectral observations of the Puppis A supernova remnant (SNR) with the Spitzer Space Telescope confirm that its IR emission is dominated by the thermal continuum emission of swept-up interstellar dust which is collisionally heated by the X-ray emitting gas of the SNR. Line emission is too weak to affect the fluxes measured in broadband observations, and is poorly correlated with the IR or X-ray emission. Modeling of spectra from regions both in the SNR and in the associated ISM show that the ubiquitous polycyclic aromatic hydrocarbons (PAHs) of the ISM are destroyed within the SNR, along with nearly 25% of the mass of graphite and silicate dust grains.

Arendt, Richard G.↗
NASA NTRS2011

On the Location of the gamma-Ray Outburst Emission in the BL Lacertae Object AO 0235 + 164 Through Observations Across the Electromagnetic Spectrum

We present observations of a major outburst at centimeter, millimeter, optical, X-ray, and gamma-ray wavelengths of the BL Lacertae object AO 0235+164. We analyze the timing of multi-waveband variations in the flux and linear polarization, as well as changes in Very Long Baseline Array images at A = 7 mm with approx.0.15 milliarcsec resolution. The association of the events at different wavebands is confirmed at high statistical significance by probability arguments and Monte Carlo simulations. A series of sharp peaks in optical linear polarization, as well as a pronounced maximum in the 7 mm polarization of a superluminal jet knot, indicate rapid fluctuations in the degree of ordering of the magnetic field. These results lead us to conclude that the outburst occurred in the jet both in the quasi-stationary "core" and in the superluminal knot, both parsecs downstream of the supermassive black hole. We interpret the outburst as a consequence of the propagation of a disturbance, elongated along the line of sight by light-travel time delays, that passes through a standing recollimation shock in the core and propagates down the jet to create the superluminal knot. The multi-wavelength light curves vary together on long timescales (months/ years), but the correspondence is poorer on shorter timescales. This, as well as the variability of the polarization and the dual location of the outburst, agrees with the expectations of a multi-zone emission model in which turbulence plays a major role in modulating the synchrotron and inverse Compton fluxes.

Agudo, Ivan↗
NASA NTRS2012

X-Ray Emission from the Wolf-Rayet Bubble S 308

The Wolf-Rayet (WR) bubble S 308 around the WR star HD 50896 is one of the only two WR bubbles known to possess X-ray emission. We present XMM-Newton observations of three fields of this WR bubble that, in conjunction with an existing observation of its Northwest quadrant (Chu et al. 2003), map most of the nebula. The X-ray emission from S 308 displays a limb-brightened morphology, with a 22' in size central cavity and a shell thickness of approx. 8'. This X-ray shell is confined by the optical shell of ionized material. The spectrum is dominated by the He-like triplets of N VI at approx.0.43 keV and O VII at approx.0.5 keV, and declines towards high energies, with a faint tail up to 1 keV. This spectrum can be described by a two-temperature optically thin plasma emission model (T1 approx.1.1 x 10(exp 6) K, T2 approx.13 x 10(exp 6) K), with a total X-ray luminosity approx.3 x 10(exp 33) erg/s at the assumed distance of 1.8 kpc. Qualitative comparison of the X-ray morphology of S 308 with the results of numerical simulations of wind-blown WR bubbles suggests a progenitor mass of 40 Stellar mass and an age in the WR phase approx.20,000 yrs. The X-ray luminosity predicted by simulatioms including the effects of heat conduction is in agreement with the observations, however, the simulated X-ray spectrum indicates generally hotter gas than is derived from the observations. We suggest that non-equilibrium ionization (NEI) may provide an explanation for this discrepancy.

Toala, J. A.↗
NASA NTRS2011

A Critical Examination of Spatial Biases Between MODIS and MISR Aerosol Products - Application for Potential AERONET Deployment

AErosol RObotic NETwork (AERONET) data are the primary benchmark for evaluating satellite-retrieved aerosol properties. However, despite its extensive coverage, the representativeness of the AERONET data is rarely discussed. Indeed, many studies have shown that satellite retrieval biases have a significant degree of spatial correlation that may be problematic for higher-level processes or inverse-emissions-modeling studies. To consider these issues and evaluate relative performance in regions of few surface observations, cross-comparisons between the Aerosol Optical Depth (AOD) products of operational MODIS Collection 5.1 Dark Target (DT) and operational MODIS Collection 5.1 Deep Blue (DB) with MISR version 22 were conducted. Through such comparisons, we can observe coherent spatial features of the AOD bias while side-stepping the full analysis required for determining when or where either retrieval is more correct. We identify regions where MODIS to MISR AOD ratios were found to be above 1.4 and below 0.7. Regions where lower boundary condition uncertainty is likely to be a dominant factor include portions of Western North America, the Andes mountains, Saharan Africa, the Arabian Peninsula, and Central Asia. Similarly, microphysical biases may be an issue in South America, and specific parts of Southern Africa, India Asia, East Asia, and Indonesia. These results help identify high-priority locations for possible future deployments of both in situ and ground based remote sensing measurements. The Supplement includes a km1 file.

Shi, Y.↗
NASA NTRS2012

Soil Moisture Active/Passive (SMAP) Forward Brightness Temperature Simulator

The SMAP is one of four first-tier missions recommended by the US National Research Council's Committee on Earth Science and Applications from Space (Earth Science and Applications from Space: National Imperatives for the Next Decade and Beyond, Space Studies Board, National Academies Press, 2007) [1]. It is to measure the global soil moisture and freeze/thaw from space. One of the spaceborne instruments is an L-band radiometer with a shared single feedhorn and parabolic mesh reflector. While the radiometer measures the emission over a footprint of interest, unwanted emissions are also received by the antenna through the antenna sidelobes from the cosmic background and other error sources such as the Sun, the Moon and the galaxy. Their effects need to be considered accurately, and the analysis of the overall performance of the radiometer requires end-to-end performance simulation from Earth emission to antenna brightness temperature, such as the global simulation of L-band brightness temperature simulation over land and sea [2]. To assist with the SMAP radiometer level 1B algorithm development, the SMAP forward brightness temperature simulator is developed by adapting the Aquarius simulator [2] with necessary modifications. This poster presents the current status of the SMAP forward brightness simulator s development including incorporating the land microwave emission model and its input datasets, and a simplified atmospheric radiative transfer model. The latest simulation results are also presented to demonstrate the ability of supporting the SMAP L1B algorithm development.

Peng, Jinzheng↗
NASA NTRS2010

On the Phase-Averaged Spectrum of Pulsars and Shape of Their Cutoffs

All gamma ray pulsars exhibit an exponential cutoff in their spectra and for bright pulsars the statistics are sufficiently high to study the detailed shape of the cutoff. The phase averaged spectra of some pulsars exhibit a sub-exponential cutoff, not predicted by any single physical mechanism. Further studies clarified that (his gentler average cutoff is a consequence of having significant variations of the cutoff energy in the phase-resolved spectrum. In conclusion, the phase-averaged spectrum of a pulsar is not a physical quantity to test high-energy emission models.

Celik, O.↗
NASA NTRS2013

Spatial and Temporal Dust Source Variability in Northern China Identified Using Advanced Remote Sensing Analysis

The aim of this research is to provide a detailed characterization of spatial patterns and temporal trends in the regional and local dust source areas within the desert of the Alashan Prefecture (Inner Mongolia, China). This problem was approached through multi-scale remote sensing analysis of vegetation changes. The primary requirements for this regional analysis are high spatial and spectral resolution data, accurate spectral calibration and good temporal resolution with a suitable temporal baseline. Landsat analysis and field validation along with the low spatial resolution classifications from MODIS and AVHRR are combined to provide a reliable characterization of the different potential dust-producing sources. The representation of intra-annual and inter-annual Normalized Difference Vegetation Index (NDVI) trend to assess land cover discrimination for mapping potential dust source using MODIS and AVHRR at larger scale is enhanced by Landsat Spectral Mixing Analysis (SMA). The combined methodology is to determine the extent to which Landsat can distinguish important soils types in order to better understand how soil reflectance behaves at seasonal and inter-annual timescales. As a final result mapping soil surface properties using SMA is representative of responses of different land and soil cover previously identified by NDVI trend. The results could be used in dust emission models even if they are not reflecting aggregate formation, soil stability or particle coatings showing to be critical for accurately represent dust source over different regional and local emitting areas.

spectral mixing analysis↗