Search Publications
Swift and XMM-Newton Observations of the Extraordinary Gamma-Ray Burst 060729: More than 125 Days of X-Ray Afterglow
Sakamoto, Takanori; Cummings, Jay; Gronwall, Caryl +24 more
We report the results of the Swift and XMM-Newton observations of the Swift -discovered GRB 060729 (T90=115 s). The afterglow of this burst was exceptionally bright in X-rays as well as at UV/optical wavelengths, showing an unusually long slow decay phase (α=0.14+/-0.02), suggesting a larger energy injection phase at early times than in…
GRB 061121: Broadband Spectral Evolution through the Prompt and Afterglow Phases of a Bright Burst
Troja, E.; Sakamoto, T.; Melandri, A. +33 more
Swift triggered on a precursor to the main burst of GRB 061121 (z=1.314), allowing observations to be made from the optical to gamma-ray bands. Many other telescopes, including Konus-Wind, XMM-Newton, ROTSE, and the Faulkes Telescope North, also observed the burst. The gamma-ray, X-ray, and UV/optical emission all showed a peak ~75 s after the tri…
A Morphological Study of Gamma-Ray Burst Host Galaxies
Berger, E.; Penprase, B. E.; Wainwright, C.
We present a comprehensive study of the morphological properties of 42 γ-ray burst (GRB) host galaxies imaged with the Hubble Space Telescope in the optical band. The purpose of this study is to understand the relation of GRBs to their macroenvironments and to compare the GRB-selected galaxies to other high-redshift samples. We perform both qualit…
The Coronal Heating Paradox
Peter, Hardi; Aschwanden, Markus J.; Winebarger, Amy +1 more
The ``coronal heating problem'' has been with us over 60 years, and hundreds of theoretical models have been proposed without an obvious solution in sight. In this paper we point out that observations show no evidence for local heating in the solar corona, but rather for heating below the corona in the transition region and upper chromosphere, wit…
Super Star Cluster Velocity Dispersions and Virial Masses in the M82 Nuclear Starburst
Graham, James R.; McCrady, Nate
We use high-resolution near-infrared spectroscopy from Keck Observatory to measure the stellar velocity dispersions of 19 super star clusters (SSCs) in the nuclear starburst of M82. The clusters have ages on the order of 10 Myr, which is many times longer than the crossing times implied by their velocity dispersions and radii. We therefore apply t…
Why Haven't Loose Globular Clusters Collapsed Yet?
Paresce, Francesco; De Marchi, Guido; Pulone, Luigi
We report on the discovery of a surprising observed correlation between the slope of the low-mass stellar global mass function (GMF) of globular clusters (GCs) and their central concentration parameter c=log(rt/rc), i.e., the logarithmic ratio of tidal and core radii. This result is based on the analysis of a sample of 20 Gal…
The ACS Fornax Cluster Survey. II. The Central Brightness Profiles of Early-Type Galaxies: A Characteristic Radius on Nuclear Scales and the Transition from Central Luminosity Deficit to Excess
Jordán, Andrés; Infante, Leopoldo; Tonry, John L. +9 more
We analyze brightness profiles for 143 early-type galaxies in the Virgo and Fornax Clusters, observed with the Advanced Camera for Surveys on the Hubble Space Telescope. Sérsic models are found to provide accurate representations of the global profiles with a notable exception: the observed profiles deviate systematically inside a characteristic `…
Simultaneous Multiwavelength Observations of the Low/Hard State of the X-Ray Transient Source SWIFT J1753.5-0127
D'Avanzo, P.; Frontera, F.; Goldoni, P. +11 more
We report the results of simultaneous multiwavelength observations of the X-ray transient source SWIFT J1753.5-0127 performed with INTEGRAL, RXTE, NTT, REM, and VLA on 2005 August 10-12. The source, which underwent an X-ray outburst since 2005 May 30, was observed during the INTEGRAL Target of Opportunity program dedicated to new X-ray novae locat…
Interaction between a Fast Rotating Sunspot and Ephemeral Regions as the Origin of the Major Solar Event on 2006 December 13
Zhang, Jun; Li, Leping; Song, Qiao
The major solar event on 2006 December 13 is characterized by the approximately simultaneous occurrence of a heap of hot ejecta, a great two-ribbon flare, and an extended Earth-directed coronal mass ejection. We examine the magnetic field and sunspot evolution in NOAA AR 10930, the source region of the event, while it transited the solar disk cent…
The Discovery of Cepheids and a Distance to NGC 5128
Ajhar, Edward A.; Stetson, Peter B.; Tonry, John L. +3 more
We discuss a new distance to NGC 5128 (Centaurus A) based on Cepheid variables observed with the Hubble Space Telescope. Twelve F555W (V) and six F814W (I) epochs of cosmic-ray-split WFPC2 observations were obtained. A total of 56 bona fide Cepheids were discovered, with periods ranging from 5 to ~50 days; five of these are likely Population II Ce…