Search Publications
Evidence of an Intermediate-Mass Black Hole: Chandra and XMM-Newton Observations of the Ultraluminous Supersoft X-Ray Source in M101 during Its 2004 Outburst
Kong, A. K. H.; Yuan, F.; Di Stefano, R.
We report the results of Chandra and XMM-Newton observations of a new outburst of an ultraluminous supersoft X-ray source in M101. CXOU J140332.3+542103 was observed in a low-luminosity state (LX~1037 ergs s-1) between 2004 January and May. The low-state X-ray spectra were relatively hard; the combined low-state sp…
NGC 3125-1: The Most Extreme Wolf-Rayet Star Cluster Known in the Local Universe
Leitherer, Claus; Chandar, Rupali; Tremonti, Christy A.
We use Space Telescope Imaging Spectrograph long-slit ultraviolet spectroscopy of local starburst galaxies to study the massive star content of a representative sample of super-star clusters, with a primary focus on their Wolf-Rayet (W-R) content as measured from the He II λ1640 emission feature. The goals of this work are threefold. First, we qua…
An X-Ray Jet from a White Dwarf: Detection of the Collimated Outflow from CH Cygni with Chandra
Sokoloski, J. L.; Galloway, Duncan K.
Most symbiotic stars consist of a white dwarf accreting material from the wind of a red giant. An increasing number of these objects have been found to produce jets. Analysis of archival Chandra data of the symbiotic system CH Cygni reveals faint extended emission to the south, aligned with the optical and radio jets seen in earlier Hubble Space T…
Helicity Patterns of Coronal Mass Ejection-associated Active Regions
Zhang, Jun; Wang, Jingxiu; Zhou, Guiping
Coronal mass ejections (CMEs) are thought to originate from the overaccumulation of magnetic helicity. While recent studies have revealed the inability of active region (AR) fields to create enough helicity for CMEs, we have tried, on the other hand, to examine whether particular helicity patterns are retained by CME-associated ARs. Nine ARs, whos…
Unveiling the Central Parsec Region of an Active Galactic Nucleus: The Circinus Nucleus in the Near-Infrared with the Very Large Telescope
Lutz, D.; Rouan, D.; Meisenheimer, K. +12 more
VLT J- to M'-band adaptive optics observations of the Circinus galaxy on parsec scales resolve a central bright Ks-band source with a FWHM size of 1.9+/-0.6 pc. This source is only visible at wavelengths longward of 1.6 µm and coincides in position with the peak of the [Si VII] 2.48 µm coronal line emission. With respect to …
Green Bank Telescope Discovery of Two Binary Millisecond Pulsars in the Globular Cluster M30
Ransom, Scott M.; Kaspi, Victoria M.; Hessels, Jason W. T. +4 more
We report the discovery of two binary millisecond pulsars in the core-collapsed globular cluster M30 using the Green Bank Telescope (GBT) at 20 cm. PSR J2140-2310A (M30A) is an eclipsing 11 ms pulsar in a 4 hr circular orbit, and PSR J2140-23B (M30B) is a 13 ms pulsar in an as yet undetermined but most likely highly eccentric (e>0.5) and relati…
Location of the Optical Reverse Shock in the Cassiopeia A Supernova Remnant
Chevalier, Roger A.; Borkowski, Kazimierz J.; van den Bergh, Sidney +4 more
We use two epochs of Hubble Space Telescope WFPC2 images separated by 2 yr to determine the location and propagation of the reverse shock (RS) in the young supernova remnant Cassiopeia A (Cas A). The images trace optical line emission from fast-moving knots and filaments of highly processed ejecta as they cross the RS, become heated and compressed…
RHESSI e+-e- Annihilation Radiation Observations: Implications for Conditions in the Flaring Solar Chromosphere
Smith, David M.; Lin, Robert P.; Share, Gerald H. +2 more
RHESSI has measured the positron-electron annihilation line and continuum in three solar flares: 2002 July 23, 2003 October 28, and 2003 November 2. The 511 keV line was broad (~4-8 keV) in all three flares, consistent with annihilations in an ambient ionized medium at temperatures above 105 K. The measured continuum from positronium an…
XMM-Newton Observations of PSR B1706-44
Cropper, M.; McGowan, K. E.; Kennea, J. A. +5 more
We report on the XMM-Newton observations of the young 102 ms pulsar PSR B1706-44. We have found that both a blackbody plus power law and a magnetized atmospheric model plus power law provide an excellent fit to the European Photon Imaging Camera (EPIC) spectra. The two scenarios are therefore indistinguishable on a statistical basis, although we a…
The Dynamical Distance to M15: Estimates of the Cluster's Age and Mass and of the Absolute Magnitude of Its RR Lyrae Stars
Baumgardt, H.; Harrison, T. E.; McNamara, B. J.
Newly determined high-precision relative proper motions determined from the Hubble Space Telescope Wide Field Planetary Camera 2 are used along with radial velocity measurements to determine the dynamical distance to the globular cluster M15. A comparison of the proper motion and radial velocity dispersions from a sample of 237 stars, located at a…