Search Publications
Revisiting the population of Galactic open clusters
Scholz, R. -D.; Piskunov, A. E.; Kharchenko, N. V. +2 more
We present results of a study of the galactic open cluster population based on the all-sky catalogue ASCC-2.5 (I/280A) compiled from Tycho-2, Hipparcos and other catalogues. The sample of optical clusters from ASCC-2.5 is complete up to about 850 pc from the Sun. The symmetry plane of the clusters' distribution is determined to be at Z_0=-22±4 pc,…
Local structure of the magnetotail current sheet: 2001 Cluster observations
Sauvaud, J. -A.; Balogh, A.; Zhang, T. L. +10 more
Thirty rapid crossings of the magnetotail current sheet by the Cluster spacecraft during July-October 2001 at a geocentric distance of 19 RE are examined in detail to address the structure of the current sheet. We use four-point magnetic field measurements to estimate electric current density; the current sheet spatial scale is estimate…
The soft X-ray/NLR connection: a single photoionized medium?
Bianchi, S.; Guainazzi, M.; Chiaberge, M.
We present a sample of 8 nearby Seyfert 2 galaxies observed by HST and Chandra. All of the sources present soft X-ray emission which is coincident in extension and overall morphology with the [O iii] emission. The spectral analysis reveals that the soft X-ray emission of all the objects is likely to be dominated by a photoionized gas. This is stro…
Stringent Constraint on Galactic Positron Production
Beacom, John F.; Yüksel, Hasan
The intense 0.511 MeV gamma-ray line emission from the Galactic Center observed by INTEGRAL requires a large annihilation rate of nonrelativistic positrons. If these positrons are injected at even mildly relativistic energies, higher-energy gamma rays will also be produced. We calculate the gamma-ray spectrum due to inflight annihilation and compa…
Variations in solar luminosity and their effect on the Earth's climate
Fröhlich, C.; Foukal, P.; Spruit, H. +1 more
Variations in the Sun's total energy output (luminosity) are caused by changing dark (sunspot) and bright structures on the solar disk during the 11-year sunspot cycle. The variations measured from spacecraft since 1978 are too small to have contributed appreciably to accelerated global warming over the past 30 years. In this Review, we show that …
X-ray spectral survey with XMM-Newton of a complete sample of nearby Seyfert galaxies
Cappi, M.; Filippenko, A. V.; Piconcelli, E. +15 more
Results obtained from an X-ray spectral survey of nearby Seyfert galaxies using XMM-Newton are reported. The sample was optically selected, well defined, complete in B magnitude, and distance limited: it consists of the nearest (D ⪉22 Mpc) 27 Seyfert galaxies (9 of type 1, 18 of type 2) taken from the Ho et al. (1997a, ApJS, 112, 315) sample. This…
Constraints on sterile neutrinos as dark matter candidates from the diffuse X-ray background
Neronov, A.; Boyarsky, A.; Ruchayskiy, O. +1 more
Sterile neutrinos with masses in the kilo-electronvolt range are viable candidates for the warm dark matter. We analyse existing data for the extragalactic diffuse X-ray background for signatures of sterile neutrino decay. The absence of a detectable signal within current uncertainties of background measurements puts model-independent constraints …
2MASS wide field extinction maps. I. The Pipe nebula
Alves, J.; Lombardi, M.; Lada, C. J.
Context: .
Aims: . We present a 8°×6°, high resolution extinction map of the Pipe nebula using 4.5 million stars from the Two Micron All Sky Survey (2MASS) point source catalog.
Methods: . The use of Nicer (Lombardi & Alves 2001, A&A, 377, 1023), a robust and optimal technique to map the dust column density, allows us to detect a…
Strategy for Searching for a Dark Matter Sterile Neutrino
Neronov, A.; Boyarsky, A.; Ruchayskiy, O. +2 more
We propose a strategy for how to look for dark matter particles possessing a radiative decay channel and derive constraints on their parameters from observations of x rays from our own Galaxy and its dwarf satellites. When applied to sterile neutrinos in the keV mass range this approach gives a significant improvement to restrictions on neutrino p…
Discovery of Luminous Pulsed Hard X-Ray Emission from Anomalous X-Ray Pulsars 1RXS J1708-4009, 4U 0142+61, and 1E 2259+586 by INTEGRAL and RXTE
Kuiper, L.; Hermsen, W.; den Hartog, P. R. +1 more
We investigated the time-averaged high-energy spectral characteristics of the persistent anomalous X-ray pulsars (AXPs) 1RXS J1708-4009, 4U 0142+61, 1E 2259+586, and 1E 1048.1-5937, using RXTE PCA (2-60 keV), RXTE HEXTE (15-250 keV), and INTEGRAL IBIS ISGRI (20-300 keV) data. We discovered hard spectral tails for energies above 10 keV in the total…