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Longitudinal Magnetic Field Changes Accompanying Solar Flares
Harvey, J. W.; Sudol, J. J.
We have used Global Oscillation Network Group (GONG) magnetograms to characterize the changes in the photospheric longitudinal magnetic field during 15 X-class solar flares. An abrupt, significant, and persistent change in the magnetic field occurred in at least one location within the flaring active region during each event. We have identified a …
Radio and Plasma Wave Observations at Saturn from Cassini's Approach and First Orbit
Gurnett, D. A.; Persoon, A. M.; Hospodarsky, G. B. +24 more
We report data from the Cassini radio and plasma wave instrument during the approach and first orbit at Saturn. During the approach, radio emissions from Saturn showed that the radio rotation period is now 10 hours 45 minutes 45 +/- 36 seconds, about 6 minutes longer than measured by Voyager in 1980 to 1981. In addition, many intense impulsive rad…
The Local Group and Other Neighboring Galaxy Groups
Karachentsev, I. D.
Over the last few years, rapid progress has been made in distance measurements for nearby galaxies based on the magnitude of stars on the tip of the red giant branch. Current CCD surveys with the Hubble Space Telescope (HST) and large ground-based telescopes bring ~10% accurate distances for roughly a hundred galaxies within 5 Mpc. The new data on…
Cassini Radar Views the Surface of Titan
Stiles, B.; Kelleher, K.; Callahan, P. +32 more
The Cassini Titan Radar Mapper imaged about 1% of Titan's surface at a resolution of ~0.5 kilometer, and larger areas of the globe in lower resolution modes. The images reveal a complex surface, with areas of low relief and a variety of geologic features suggestive of dome-like volcanic constructs, flows, and sinuous channels. The surface appears …
Gamma-Ray Constraint on Galactic Positron Production by MeV Dark Matter
Bertone, Gianfranco; Beacom, John F.; Bell, Nicole F.
The Galactic positrons, as observed by their annihilation gamma-ray line at 0.511 MeV, are difficult to account for with astrophysical sources. It has been proposed that they are produced instead by dark matter annihilation or decay in the inner Galactic halo. To avoid other constraints, these processes are required to occur “invisibly,” such that…
Spectroscopy of polycyclic aromatic hydrocarbons and very small grains in photodissociation regions
Joblin, C.; Rapacioli, M.; Boissel, P.
We have coupled a singular value decomposition method with a Monte Carlo search algorithm to analyse the mid-infrared ISOCAM spectral maps of photodissociation regions (PDRs) in NGC 7023 and ρ Oph-SR3.Three different spectra and their associated spatial distribution were extracted from this analysis. It is shown that they can be associated with po…
Evolution since z = 1 of the Morphology-Density Relation for Galaxies
Smith, Graham P.; Treu, Tommaso; Ellis, Richard S. +2 more
We measure the morphology-density relation of galaxies at z=1 across the full 3 orders of magnitude in projected galaxy density available in low-redshift studies. Our study adopts techniques that are comparable with those applied at lower redshifts, allowing a direct investigation of how the morphological segregation of galaxies has evolved over t…
The unresolved hard X-ray background: the missing source population implied by the Chandra and XMM-Newton deep fields
Alexander, D. M.; Bauer, F. E.; Brandt, W. N. +6 more
We extend our earlier work on X-ray source stacking in the deep XMM-Newton observation of the Lockman Hole, to the 2-Ms Chandra Deep Field North (CDF-N) and the 1-Ms Chandra Deep Field South (CDF-S). The XMM-Newton work showed the resolved fraction of the X-ray background (XRB) to be ~80-100 per cent at <~ 2keV but this decreased to only ~50 pe…
INTEGRAL observations of recurrent fast X-ray transient sources
Hill, A. B.; Bird, A. J.; Ubertini, P. +9 more
Fast X-ray Transients (FXTs) are believed to be non-recurrent bright X-ray sources lasting less than a day and occuring at serendipitous positions, they can best be detected and discovered by instruments having a sufficiently wide field of view and high sensitivity. The IBIS/ISGRI instrument onboard INTEGRAL is particularly suited to detect new or…
A Deep Chandra Survey of the Globular Cluster 47 Tucanae: Catalog of Point Sources
Heinke, C. O.; Cohn, H. N.; Lugger, P. M. +5 more
We have detected 300 X-ray sources within the half-mass radius (2.79 arcmin) of the globular cluster 47 Tucanae in a deep (281 ks) Chandra exposure. We perform photometry and simple spectral fitting for our detected sources and construct luminosity functions, X-ray color-magnitude, and color-color diagrams. Eighty-seven X-ray sources show variabil…