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Ultraviolet and Multiwavelength Variability of the Blazar 3C 279: Evidence for Thermal Emission
Maraschi, L.; Chiappetti, L.; Pian, E. +13 more
The γ-ray blazar 3C 279 was monitored on a nearly daily basis with IUE, ROSAT, and EGRET for 3 weeks between 1992 December and 1993 January. During this period, the blazar was at a historical minimum at all wavelengths. Here we present the UV data obtained during this multiwavelength campaign. A maximum UV variation of ~50% is detected, while duri…
Analysis of Transition-Region Emission-Line Profiles from Full-Disk Scans of the Sun Using the SUMER Instrument on SOHO
Peter, H.
We examine statistical properties of line profiles seen in full-disk observations with the UV spectrograph SUMER on board SOHO. In the SUMER data archive, full-disk data with complete spectral information are available only for wavelength regions including the He I (584 Å), Ne VIII (770 Å), C III (977 Å) and C IV (1548 Å) emission lines. In this p…
Interstellar Abundances in the Magellanic Clouds. II. The Line of Sight to SN 1987A in the Large Magellanic Cloud
Sonneborn, G.; Frisch, P. C.; York, D. G. +1 more
We have analyzed both high-resolution optical absorption-line spectra and UV spectra obtained with IUE of the LMC SN 1987A, in order to determine abundances and physical conditions in the various neutral interstellar clouds along the line of sight to the supernova (SN). We have used a flat-fielding procedure to enhance the signal-to-noise ratios (…
Ring Diagram Analysis of Near-Surface Flows in the Sun
Basu, Sarbani; Antia, H. M.; Tripathy, S. C.
Ring diagram analysis of solar oscillation power spectra obtained from Michelson Doppler Imager data is carried out to study the velocity fields in the outer part of the solar convection zone. The three-dimensional power spectra are fitted to a model that has a Lorentzian profile in frequency and includes the advection of the wave front by horizon…
Properties of Quiet-Sun Coronal Plasmas at Distances of 1.03<=Rsolar<=1.50 along the Solar Equatorial Plane
Wilhelm, K.; Schühle, U.; Doschek, G. A. +1 more
We determine the physical properties, i.e., electron temperature, density, line-of-sight emission measure, and element-abundance variation with height, in the Sun's equatorial west limb streamer region from extreme-ultraviolet (EUV) spectra recorded by the Solar Ultraviolet Measurements of Emitted Radiation (SUMER) spectrometer on the Solar and He…
The Fading Optical Counterpart of GRB 970228, 6 Months and 1 Year Later
Fruchter, Andrew S.; Mutchler, Max; Livio, Mario +20 more
We report on observations of the fading optical counterpart of the gamma-ray burst GRB 970228, made with the Hubble Space Telescope (HST) and the Keck I telescope. The gamma-ray burst (GRB) was observed approximately 6 months after outburst, on 1997 September 4, using the HST/STIS CCD, and approximately 1 year after outburst, on 1998 February 24, …
Plasma Diagnostics of Transition Region ``Moss'' using SOHO/CDS and TRACE
De Pontieu, Bart; Fletcher, Lyndsay
Recent observations of solar active regions with the Transition Region and Coronal Explorer (TRACE) have revealed finely textured, low-lying EUV emission, called the ``moss,'' appearing as a bright dynamic pattern with dark inclusions. The moss has been interpreted as the upper transition region by Berger and coworkers. In this study we use SOHO C…
Nuclear Disks of Gas and Dust in Early-Type Galaxies and the Hunt for Massive Black Holes: Hubble Space Telescope Observations of NGC 6251
Ferrarese, Laura; Ford, Holland C.
We discuss Hubble Space Telescope (HST) optical images and spectra of NGC 6251, a giant E2 galaxy and powerful radio source at a distance of 106 Mpc (for H0=70 km s-1 Mpc-1). The galaxy is known to host a very well-defined dust disk; the exceptional resolution of our V and I images allows a detailed study of the di…
ISO LWS Spectroscopy of M82: A Unified Evolutionary Model
Smith, Howard A.; Satyapal, Shobita; Spinoglio, Luigi +9 more
We present the first complete far-infrared spectrum (43-197 µm) of M82, the brightest infrared galaxy in the sky, taken with the Long Wavelength Spectrometer of the Infrared Space Observatory (ISO). We detected seven fine structure emission lines, [O I] 63 and 145 µm, [O III] 52 and 88 µm , [N II] 122 µm, [N III] 57 µ…
High-Redshift Supernovae in the Hubble Deep Field
Phillips, M. M.; Gilliland, Ronald L.; Nugent, Peter E.
Two supernovae detected in the Hubble Deep Field (HDF) using the original 1995 December epoch and data from a shorter (63,000 s in F814W) 1997 December visit with HST are discussed. The supernovae (SNe) are both associated with distinct galaxies at redshifts of 0.95 (spectroscopic) from Cohen et al. and 1.32 (photometric) from the work of Fernánde…