Search Publications
Coronal Heating and Photospheric Turbulence Parameters: Observational Aspects
Romano, P.; Abramenko, V. I.; Pevtsov, A. A.
In this study, the soft X-ray luminosity of the solar corona, measured by the Yohkoh spacecraft for 104 well-developed and decaying active regions, is compared to the magnetic field parameters determined from SOHO MDI high-resolution magnetograms. We calculate and compare (1) two area-independent characteristics of the magnetic field: the index (α…
A Spectroscopic Study of the Star-Forming Properties of the Center of NGC 4194
Kaiser, M. E.; Weistrop, D.; Nelson, C. H. +1 more
We have obtained Space Telescope Imaging Spectrograph long-slit spectra of the central region of the advanced merger NGC 4194. The spectra cover the wavelength ranges 1150-1750 Å in the UV and 2900-10270 Å in the visible. Results from the study of the properties of 14 star-forming regions (knots) are presented. If the [N II] contribution is 40% of…
The weak INTEGRAL bursts GRB 040223 and GRB 040624 : an emerging population of dark afterglows
Covino, S.; D'Avanzo, P.; Campana, S. +18 more
We report here γ-ray, X-ray and near-infrared observations of
Evolution of depressions on Comet 67P/Churyumov Gerasimenko: Role of ice metamorphism
Kossacki, Konrad J.; Leliwa-Kopystyński, Jacek; Szutowicz, Slawomira
This work is intended to investigate the influence of temperature-dependent metamorphism of ice on the shape of small depressions in the surface of cometary nuclei. We are mainly interested in the role of initial cohesivity of a nucleus. For this purpose we simulate sublimation of ice from the facets of initially cylindrical depressions in ice of …
Tracing the Dynamical History of the Globular Cluster 47 Tucanae
Sills, Alison; Beccari, Giacomo; Guhathakurta, Puragra +3 more
We use two stellar populations in the globular cluster 47 Tucanae to trace its dynamical history: blue stragglers and low-mass main-sequence stars. We assumed that the blue stragglers were formed through stellar collisions in all regions of the cluster. We find that in the core of the cluster, models of collisional blue stragglers agree well with …
X-rays from the radio-quiet quasar PG 1407+265: relativistic jet or accretion disc emission?
Gallo, L. C.
We present two XMM-Newton observations of the luminous (Lx > 1046ergs-1), radio-quiet quasar PG 1407+265, separated by 11 months. The data indicate two distinct states: a highly variable, bright state (first epoch); and a quiescent, low-flux one (second epoch). During the low-flux state the spectrum is consisten…
Bistatic observations of Titan's surface with the Huygens probe radio signal
Lorenz, R. D.; Lebreton, J. -P.; Floury, N. +2 more
Huygens provided an unanticipated bistatic radio scattering experiment from Titan's surface. After a successful entry and descent on Titan, on 14 January 2005, the probe remarkably survived the landing and continued radioing from the surface to the overflying Cassini, until the orbiter set below Titan's local horizon. Here we report high-quality m…
On the Fraction of X-Ray-obscured Quasars in the Local Universe
Wang, J. X.; Jiang, P.
Recent wide-area hard X-ray and soft gamma-ray surveys have shown that the fraction of X-ray-obscured active galactic nuclei (AGNs) in the local universe significantly decreases with intrinsic luminosity. In this Letter we point out that two corrections have to be made to the samples: (1) radio-loud AGNs have to be excluded, since their X-ray emis…
Multiwavelength Studies of the Optically Dark Gamma-Ray Burst 001025A
Cline, T.; Hurley, K.; Schartel, N. +18 more
We identify the fading X-ray afterglow of GRB 001025A from XMM-Newton observations obtained 1.9-2.3 days, 2 yr, and 2.5 yr after the burst. The nondetection of an optical counterpart to an upper limit of R=25.5, 1.20 days after the burst, makes GRB 001025A a ``dark'' burst. Based on the X-ray afterglow spectral properties of GRB 001025A, we argue …
Variable Unidentified Emission near 6307 Å in η Carinae
Weis, K.; Stahl, O.; Davidson, K. +2 more
We have discovered a conspicuous unidentified variable feature near 6307 Å in the spectrum of η Carinae that is spatially unresolved from the central star and its wind (r<~200-300 AU). It is significant for two reasons: first, such prominent unidentified lines are now rare in this object, and second, this feature varies strongly and systematica…