Search Publications
A Galactic Origin for the Local Ionized X-Ray Absorbers
Canizares, Claude R.; Wolfire, Mark; Fang, Taotao +1 more
Recent Chandra and XMM-Newton observations of distant quasars have shown strong local (z~0) X-ray absorption lines from highly ionized gas, primarily He-like oxygen. The nature of these X-ray absorbers, i.e., whether they are part of the hot gas associated with the Milky Way or part of the intragroup medium in the Local Group, remains a puzzle due…
XMM-Newton Observations of Four Millisecond Pulsars
Zavlin, Vyacheslav E.
I present an analysis of the XMM-Newton observations of four millisecond pulsars, J0437-4715, J2124-3358, J1024-0719, and J0034-0534. The new data provide strong evidence of thermal emission in the X-ray flux detected from the first three objects. This thermal component is best interpreted as radiation from pulsar polar caps covered with a nonmagn…
XTE J1739-302 as a Supergiant Fast X-Ray Transient
Negueruela, I.; Swank, J. H.; Markwardt, C. B. +4 more
XTE J1739-302 is a transient X-ray source with unusually short outbursts, lasting on the order of hours. Here we give a summary of X-ray observations we have made of this object in outburst with the Rossi X-Ray Timing Explorer (RXTE) and at a low level of activity with the Chandra X-Ray Observatory, as well as observations made by other groups. Vi…
Discovery of a Population of Pre-Main-Sequence Stars in NGC 346 from Deep Hubble Space Telescope ACS Images
Tosi, M.; Sabbi, E.; Nota, A. +9 more
We report the discovery of a rich population of low-mass stars in the young, massive NGC 346 star-forming region in the Small Magellanic Cloud from deep V, I, and Hα images taken with the Hubble Space Telescope Advanced Camera for Surveys. These stars have likely formed together with the NGC 346 cluster, ~=3-5 Myr ago. Their magnitudes and colors …
Evolution of the Color-Magnitude Relation in High-Redshift Clusters: Blue Early-Type Galaxies and Red Pairs in RDCS J0910+5422
Demarco, R.; Infante, L.; Zheng, W. +43 more
The color-magnitude relation has been determined for the RDCS J0910+5422 cluster of galaxies at redshift z=1.106. Cluster members were selected from the Hubble Space Telescope Advanced Camera for Surveys (HST ACS) images, combined with ground-based near-IR imaging and optical spectroscopy. The observed early-type color-magnitude relation (CMR) in …
A Persistent High-Energy Flux from the Heart of the Milky Way: INTEGRAL's View of the Galactic Center
Terrier, R.; Lund, N.; Bélanger, G. +6 more
Highly sensitive imaging observations of the Galactic center (GC) at high energies with an angular resolution of order 10' is a very recent development in the field of high-energy astrophysics. The IBIS/ISGRI imager on the INTEGRAL observatory detected for the first time a hard X-ray source, IGR J17456-2901, located within 1' of Sagittarius A* (Sg…
Molecular Gas Dynamics in NGC 6946: A Bar-driven Nuclear Starburst ``Caught in the Act''
Böker, Torsten; Schinnerer, Eva; Emsellem, Eric +1 more
We present high angular resolution (~1" and 0.6") millimeter interferometric observations of the 12CO(1-0) and 12CO(2-1) line emission in the central 300 pc of the late-type spiral galaxy NGC 6946. The data, obtained with the IRAM Plateau de Bure Interferometer (PdBI), allow the first detection of a molecular gas spiral in th…
The Magnetic Structure of Coronal Loops Observed by TRACE
López Fuentes, M. C.; Klimchuk, J. A.; Démoulin, P.
Previous studies have found that coronal loops have a nearly uniform thickness, which seems to disagree with the characteristic expansion of active region magnetic fields. This is one of the most intriguing enigmas in solar physics. We here report on the first comprehensive one-to-one comparison of observed loops with corresponding magnetic flux t…
Data-driven Magnetohydrodynamic Model for Active Region Evolution
Liu, Yang; Wu, S. T.; Hoeksema, J. Todd +1 more
We present a self-consistent, three-dimensional, magnetohydrodynamics model together with time-dependent boundary conditions based on the projected method of characteristics at the source surface (photosphere) to accommodate the observations. The new physics included in this model are differential rotation, meridional flow, effective diffusion, an…
RHESSI Observation of Chromospheric Evaporation
Liu, Wei; Liu, Siming; Jiang, Yan Wei +1 more
We present analyses of the spatial and spectral evolution of hard X-ray emission observed by RHESSI during the impulsive phase of an M1.7 flare on 2003 November 13. In general, as expected, the loop top (LT) source dominates at low energies, while the footpoint (FP) sources dominate the high-energy emission. At intermediate energies, both the LT a…