Search Publications
X-Ray Observations of Solar Long-Duration Flares
Phillips, K. J. H.; Harra, L. K.; Feldman, U.
Yohkoh X-ray observations during the several-hour decay of six large solar flares show that the main emitting region is in the form of a bright loop-top source whose spatial extent well after the impulsive stage explains most of the broadening of S XV and Ca XIX X-ray lines, which would otherwise imply nonthermal velocities of 100 km s-1
Irregular Mass Transfer in the Polars VV Puppis and V393 Pavonis during the Low State
Pandel, Dirk; Córdova, France A.
The polars VV Pup and V393 Pav were observed with XMM-Newton during states of low accretion with peak X-ray luminosities of ~1×1030 and ~1×1031 ergs s-1, respectively. In both polars, accretion onto the white dwarf was extremely irregular, and the accretion rate varied by more than 1 order of magnitude on timescale…
Rotation Rates of Particles in Saturn's Rings
Ohtsuki, Keiji
Rotational states of particles in Saturn's rings are not directly observable but have been inferred from spacecraft and ground-based observations of their thermal emission. A temperature contrast between night- and daysides of particles in Saturn's C ring during crossing of the planetary shadow has been detected and interpreted as indicating the p…
Is the INTEGRAL IBIS Source IGR J17204-3554 a Gamma-Ray-emitting Galaxy Hidden behind the Molecular Cloud NGC 6334?
Gehrels, N.; Walter, R.; Bird, A. J. +9 more
We report on the identification of a soft gamma-ray source, IGR J17204-3554, detected with IBIS, the Imager on Board the INTEGRAL Satellite. The source has a 20-100 keV flux of ~3×10-11 ergs cm-2 s-1 and is spatially coincident with NGC 6334, a molecular cloud located in the Sagittarius arm of the Milky Way. Diffus…
Dust in the Host Galaxies of Supernovae
Chary, R.; Pope, A.; Ravindranath, S. +2 more
We present Spitzer MIPS 24 µm observations of 50 supernova host galaxies at 0.1<z<1.7 in the Great Observatories Origins Deep Survey (GOODS) fields. We also discuss the detection of SN host galaxies in SCUBA/850 µm observations of GOODS-N and Spitzer Infrared Spectrograph (IRS) 16 µm observations of GOODS-S. About 60% of th…
A Variability Study of the Seyfert 2 Galaxy NGC 6300 with XMM-Newton
Awaki, Hisamitsu; Hayashida, Kiyoshi; Leighly, Karen M. +3 more
We present the results of timing analysis of the XMM-Newton observation of the Seyfert 2 galaxy NGC 6300. The hard X-ray spectrum above 2 keV consists of a Compton-thin absorbed power law, as is often seen in Seyfert 2 galaxies. We clearly detected rapid time variability on a timescale of about 1000 s from the light curve above 2 keV. The excess v…
Large-Amplitude Velocity Fluctuations in Coronal Loops: Flare Drivers?
Veltri, P.; Malara, F.; Nigro, G.
Recent space observations of coronal lines broadening during a flare occurrence suggest that unresolved nonthermal velocity rises well above the background level before the start of the flare, defined as the start of hard X-ray emission. Using a new shell model to describe the Alfvénic turbulence inside a coronal loop, it is shown that the occurre…
Nonthermal Velocities in Different Temperature Regions of the Solar Lower Transition Region
Doschek, G. A.; Mariska, J. T.; Akiyama, S.
We analyze the relationship between nonthermal velocities derived from spectral lines of ions formed at different temperatures in the solar lower transition region, using spectra from the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer on board the Solar and Heliospheric Observatory (SOHO). We find a high degree of correla…
Oxygen Abundance in Coronal Streamers
Raymond, John C.; Vásquez, Alberto M.
In a previous work we developed a stationary proton-electron MHD model of the solar corona, suitable for the minimum-activity epochs. In the present work, we use empirically derived information from the past solar minimum for the oxygen parameters (temperatures and outflow velocity) to develop an oxygen model in the frame of our previous model. So…
Spatial Evidence for Transition Radiation in a Solar Radio Burst
Fleishman, Gregory D.; Nita, Gelu M.; Gary, Dale E.
Microturbulence, i.e., enhanced fluctuations of plasma density and electric and magnetic fields, is of great interest in astrophysical plasmas, but occurs on spatial scales far too small to resolve by remote sensing, e.g., at ~1-100 cm in the solar corona. This Letter reports spatially resolved observations that offer strong support for the presen…