Search Publications
On the Absence of Wind Signatures in GRB Afterglow Spectra: Constraints on the Wolf-Rayet Winds of GRB Progenitors
Foley, Ryan J.; Ramirez-Ruiz, Enrico; Chen, Hsiao-Wen +3 more
We investigate available constraints on the circumstellar medium (CSM) around long-duration γ-ray burst (GRB) progenitors from afterglow spectra. We first establish a statistical sample of five GRB afterglow spectra that have been collected and analyzed with no prior knowledge of the line-of-sight properties. This sample is then adopted for a unif…
Static and Dynamic Modeling of a Solar Active Region
Winebarger, Amy R.; Warren, Harry P.
Recent hydrostatic simulations of solar active regions have shown that it is possible to reproduce both the total intensity and the general morphology of the high-temperature emission observed at soft X-ray wavelengths using static heating models. These static models, however, cannot account for the lower temperature emission. In addition, there i…
X-Ray Timing of PSR J1852+0040 in Kesteven 79: Evidence of Neutron Stars Weakly Magnetized at Birth
Camilo, F.; Gotthelf, E. V.; Halpern, J. P. +1 more
The 105 ms X-ray pulsar J1852+0040 is the central compact object (CCO) in supernova remnant Kes 79. We report a sensitive upper limit on its radio flux density of 12 µJy at 2 GHz using the NRAO Green Bank Telescope. Timing using the Newton X-Ray Multi-Mirror Mission (XMM-Newton) and the Chandra X-Ray Observatory over a 2.4 yr span reveals no…
The Black Hole Mass and Extreme Orbital Structure in NGC 1399
Filippenko, Alexei V.; Ho, Luis C.; Gebhardt, Karl +12 more
The largest galaxies, and in particular central galaxies in clusters, offer unique insight into understanding the mechanism for the growth of nuclear black holes. We present Hubble Space Telescope kinematics for NGC 1399, the central galaxy in Fornax. We find the best-fit model contains a black hole of (5.1+/-0.7)×108 Msolar …
Detailed Far-Ultraviolet to Optical Analysis of Four [WR] Stars
Pereira, C. B.; Hillier, D. J.; Marcolino, W. L. F. +1 more
We present far-UV to optical analyses of four hydrogen-deficient central stars of planetary nebulae: BD +30 3639, NGC 40, NGC 5315, and NGC 6905. Using the radiative transfer code CMFGEN, we determined new physical parameters and chemical abundances for these stars. The results were analyzed in the context of the [WR]-->PG 1159 evolution via th…
First X-Ray Observations of the Young Pulsar J1357-6429
Zavlin, Vyacheslav E.
The first short Chandra and XMM-Newton observations of the young and energetic pulsar J1357-6429 provided indications of a tail-like pulsar wind nebula associated with this object as well as pulsations of its X-ray flux with a pulsed fraction pf>~50% and a thermal component dominating at energies E<~2 keV. The putative nebula is v…
Ram Pressure Stripping of an Isolated Local Group Dwarf Galaxy: Evidence for an Intragroup Medium
McConnachie, Alan W.; Venn, Kim A.; Young, Lisa M. +2 more
We compare the stellar structure of the isolated, Local Group dwarf galaxy Pegasus (DDO 216) with low-resolution H I maps from L. M. Young et al. Our comparison reveals that Pegasus displays the characteristic morphology of ram pressure stripping; in particular, the H I has a ``cometary'' appearance that is not reflected in the regular, elliptical…
Vector Spectropolarimetry of Dark-cored Penumbral Filaments with Hinode
Lites, B. W.; Ichimoto, K.; Bellot Rubio, L. R. +9 more
We present spectropolarimetric measurements of dark-cored penumbral filaments taken with Hinode at a resolution of 0.3". Our observations demonstrate that dark-cored filaments are more prominent in polarized light than in continuum intensity. Far from disk center, the Stokes profiles emerging from these structures are very asymmetric and show evid…
Two SMC Symbiotic Stars Undergoing Steady Hydrogen Burning
Zezas, A.; Munari, U.; Orio, M. +2 more
Two symbiotic stars in the Small Magellanic Cloud (SMC), Lin 358 and SMC 3, have been supersoft X-ray sources (SSSs) for more than 10 years. We fit atmospheric and nebular models to their X-ray, optical, and UV spectra obtained at different epochs. The X-ray spectra are extremely soft and appear to be emitted by the white dwarf atmosphere, not by …
Forward Modeling of Hot Loop Oscillations Observed by SUMER and SXT
Erdélyi, R.; Wang, T. J.; Bradshaw, S. J. +1 more
An example of hot active region loop oscillations observed by SUMER and SXT is presented. The hypothesis that a fundamental mode standing slow sausage (acoustic) wave is initiated by a footpoint microflare is tested and confirmed using a forward modeling approach. The oscillation is set up immediately after the heating pulse. The duration, tempora…