Search Publications
Saturn's north polar cyclone and hexagon at depth revealed by Cassini/VIMS
Nicholson, Philip D.; Fletcher, Leigh N.; Baines, Kevin H. +6 more
A high-speed cyclonic vortex centered on the north pole of Saturn has been revealed by the visual-infrared mapping spectrometer (VIMS) onboard the Cassini-Huygens Orbiter, thus showing that the tropospheres of both poles of Saturn are occupied by cyclonic vortices with winds exceeding 135 m/s. High-spatial-resolution (~200 km per pixel) images acq…
Kinetic Alfvén Wave Turbulence and Transport through a Reconnection Diffusion Region
Acuna, M.; Reme, H.; Goldstein, M. L. +3 more
We demonstrate from observations that kinetic Alfvén waves may play an important role in facilitating magnetic reconnection. These waves radiate outwards from the diffusion region oblique to the magnetic field in a conelike pattern delimited by the X line separatrices with outward energy fluxes equivalent to that contained in the outstreaming ions…
Short-Term Solar Flare Prediction Using a Sequential Supervised Learning Method
Huang, Xin; Yu, Daren; Wang, Huaning +1 more
Solar flares are powered by the energy stored in magnetic fields, so evolutionary information of the magnetic field is important for short-term prediction of solar flares. However, the existing solar flare prediction models only use the current information of the active region. A sequential supervised learning method is introduced to add the evolu…
On the HI content, dust-to-gas ratio and nature of MgII absorbers
Ménard, Brice; Chelouche, Doron
We estimate the mean dust-to-gas ratio of MgII absorbers as a function of rest equivalent width W0 and redshift over the range 0.5 < z < 1.4. Using the expanded Sloan Digital Sky Survey/Hubble Space Telescope sample of low-redshift Lyman-α absorbers, we first show the existence of a 8σ correlation between the mean hydrogen column …
Strong Bursts from the Anomalous X-Ray Pulsar 1E 1547.0-5408 Observed with the INTEGRAL/SPI Anti-Coincidence Shield
Tiengo, A.; Götz, D.; Mereghetti, S. +9 more
In 2009 January, multiple short bursts of soft gamma rays were detected from the direction of the anomalous X-ray pulsar 1E 1547.0-5408 by different satellites. Here we report on the observations obtained with the Anti Coincidence Shield (ACS) of the SPI instrument on INTEGRAL during the period with the strongest bursting activity. More than 200 b…
Spectral States and Evolution of Ultraluminous X-Ray Sources
Feng, Hua; Kaaret, Philip
We examined spectral evolution in ultraluminous X-ray sources (ULXs) with apparent luminosities of about 1040 erg s-1. Based on new results in this paper, and those reported in the literature, two common spectral behaviors were found. Some ULXs in starburst galaxies have varying luminosity (L) but remain in the hard state wit…
The size-density relation of extragalactic H II regions
Hunt, L. K.; Hirashita, H.
Aims: We investigate the size-density relation in extragalactic H ii regions, with the aim of understanding the role of dust and different physical conditions in the ionized medium.
Methods: First, we compiled several observational data sets for Galactic and extragalactic H ii regions and confirm that extragalactic H ii regions follow the same…
Early Optical Observations of Gamma-Ray Bursts by the TAROT Telescopes: Period 2001-2008
Klotz, A.; Gendre, B.; Atteia, J. L. +1 more
The Télescopes à Action Rapide pour les Objets Transitoires telescopes are two robotic observatories designed to observe the prompt optical emission counterpart and the early afterglow of gamma-ray bursts (GRBs). We present data acquired between 2001 and 2008 and discuss the properties of the optical emission of GRBs, noting various interesting re…
Chandra Localizations and Spectra of Integral Sources in the Galactic Plane: The Cycle 9 Sample
Kaaret, Philip; Walter, Roland; Tomsick, John A. +2 more
We report on 0.3-10 keV X-ray observations by the Chandra X-ray Observatory of the fields of 22 sources that were discovered as hard X-ray (20-100 keV) sources by the International Gamma-Ray Astrophysics Satellite ("IGR" sources). The observations were made during Chandra's 9th observing cycle, and their purpose is to localize the sources and to m…
Testing the E peak-E iso Relation for GRBs Detected by Swift and Suzaku-WAM
Sakamoto, T.; Yamauchi, M.; Yamaoka, K. +12 more
One of the most prominent, yet controversial associations derived from the ensemble of prompt-phase observations of gamma-ray bursts (GRBs) is the apparent correlation in the source frame between the peak energy (E peak) of the νF(ν) spectrum and the isotropic radiated energy, E iso. Since most GRBs have E peak abo…