J. C. Raymond

The Ultraviolet Coronagraph Spectrometer for the Solar and Heliospheric Observatory

The SOHO Ultraviolet Coronagraph Spectrometer (UVCS/SOHO) is composed of three reflecting telescopes with external and internal occultation and a spectrometer assembly consisting of two toric grating spectrometers and a visible light polarimeter. The purpose of the UVCS instrument is to provide a body of data that can be used to address a broad range of scientific questions regarding the nature of the solar corona and the generation of the solar wind. The primary scientific goals are the following: to locate and characterize the coronal source regions of the solar wind, to identify and understand the dominant physical processes that accelerate the solar wind, to understand how the coronal plasma is heated in solar wind acceleration regions, and to increase the knowledge of coronal phenomena that control the physical properties of the solar wind as determined by in situ measurements. To progress toward these goals, the UVCS will perform ultraviolet spectroscopy and visible polarimetry to be combined with plasma diagnostic analysis techniques to provide detailed empirical descriptions of the extended solar corona from the coronal base to a heliocentric height of 12 solar radii.

Chandra/high energy transmission grating spectrometer spectroscopy of the galactic black hole GX 339-4: A relativistic iron emission line and evidence for a Seyfert-like warm absorber

We observed the Galactic black hole GX 339-4 with the Chandra High Energy Transmission Grating Spectrometer (HETGS) for 75 ks during the decline of its 2002-2003 outburst. The sensitivity of this observation provides an unprecedented glimpse of a Galactic black hole at about a tenth of the luminosity of the outburst peak. The continuum spectrum is well described by a model consisting of multicolor disk blackbody (kT~=0.6 keV) and power-law (Gamma~=2.5) components. X-ray reflection models yield improved fits. A strong, relativistic Fe Kalpha emission line is revealed, indicating that the inner disk extends to the innermost stable circular orbit. The breadth of the line is sufficient to suggest that GX 339-4 may harbor a black hole with significant angular momentum. Absorption lines from H- and He-like O and He-like Ne and Mg are detected, as well as lines that are likely due to Ne II and Ne III. The measured line properties make it difficult to associate the absorption with the coronal phase of the interstellar medium. A scenario wherein the absorption lines are due to an intrinsic AGN-like warm-absorber geometry-perhaps produced by a disk wind in an extended disk-dominated state-may be more viable. We compare our results to Chandra observations of the Galactic black hole candidate XTE J1650-500 and discuss our findings in terms of prominent models for Galactic black hole accretion flows and connections to supermassive black holes.

Elemental Abundances and Post-Coronal Mass Ejection Current Sheet in a Very Hot Active Region

A peculiar young active region was observed in 1998 March with the Ultraviolet Coronagraph Spectrometer (UVCS) over the southwest limb. The spectra showed strong emission in the λ974 line of fluorine-like iron, [Fe XVIII], which is brightest at an electron temperature of 106.8 K, and lines of Ne IX, [Ca XIV], [Ca XV], Fe XVII, [Ni XIV], and [Ni XV]. It is the only active region so far observed to show such high temperatures 0.5 R☉ above the solar limb. We derive the emission measure and estimate elemental abundances. The active region produced a number of coronal mass ejections (CMEs). After one CME on March 23, a bright post-CME arcade was seen in EIT and Yohkoh/SXT images. Between the arcade and the CME core, UVCS detected a very narrow, very hot feature, most prominently in the [Fe XVIII] line. This feature seems to be the reconnection current sheet predicted by flux rope models of CMEs. Its thickness, luminosity, and duration seem to be consistent with the expectations of the flux rope models for CME. The elemental abundances in the bright feature are enhanced by a factor of 2 compared to those in the surrounding active region, i.e., a first ionization potential enhancement of 7-8 compared to the usual factor of 3-4.

The Current Sheet Associated with the 2003 November 4 Coronal Mass Ejection: Density, Temperature, Thickness, and Line Width

In the wake of the 2003 November 4 coronal mass ejection associated with the largest solar flare of the last sunspot cycle, a current sheet (CS) was observed by the Ultraviolet Coronagraph Spectrometer (UVCS) as a narrow bright feature in the [Fe XVIII] (106.8 K) line. This is the first UV observation in which the CS evolution is followed from its onset. UV spectra provide diagnostics of electron temperature, emission measure, Doppler shift, line width, and size of the CS as function of time. Since the UVCS slit was inside the Mark IV K-coronameter (MK4) field of view, the combination of UV spectra and MK4 white light data provides estimates of the electron density and depth along the line of sight of the CS. The thickness of the CS in the [Fe XVIII] line is far larger than classical or anomalous resistivity would predict, and it might indicate an effective resistivity much larger than anomalous resistivity, such as that due to hyperdiffusion. The broad [Fe XVIII] line profiles in the CS cannot be explained as thermal widths. They result from a combination of bulk motions and turbulence. The Petschek reconnection mechanism and turbulent reconnection may be consistent with the observations.

The Role of Magnetic Reconnection in the Observable Features of Solar Eruptions

There are two competing classes of models for coronal mass ejections (CMEs): those that assume a preexisting magnetic flux rope and those that can make a flux rope during the eruption by magnetic reconnection. The present work is based on the model with a preexisting flux rope. We investigate the evolution of morphological features of the magnetic configuration in a CME according to a catastrophe model of flux rope CMEs developed previously. For the parameters chosen for the present work, roughly half of the total mass and magnetic flux are contained in the initial flux rope, while the remaining plasma and poloidal magnetic flux are brought by magnetic reconnection from the corona into the current sheet and from there into the CME bubble. These features and the corresponding physical processes are identical to those described by the non-flux rope models. Thus, the flux rope and non-flux rope models are less distinct than is generally assumed. The reconnected magnetic flux can account for the rapid expansion of the ejecta, and the plasma flowing out of the current sheet fills the outer shell of the ejecta. We tentatively identify the outer shell, the expanded bubble, and the flux rope with the leading edge, void, and core of the three-component CME structure, respectively. Thus, the final mass, speed, and magnetic energy—the quantities that determine the geoeffectiveness of the CME—are determined not in the initial eruption but during the CME expansion, at heights of a few solar radii. The aspects of this explanation that need improvement are also discussed.

The extreme ultraviolet spectrum of Alpha Aurigae (Capella)

Extreme ultraviolet spectra (λλ 70-740) of the bright spectroscopic binary system, Capella (Alpha Aurigae) obtained with the Extreme Ultraviolet Explorer satellite (EUVE), show a rich emission spectrum dominated by iron emission lines: Fe XV-XXIV. The emission measure for the system reveals a continuous distribution of plasma temperatures between 10 5 and 10 7.8 K, with a clear minimum near 10 6 K and a local maximum at 6×10 6 K. Electron density diagnostics based on Fe XXI indicate N e ≃4×10 11 -10 13 cm 3 at T e =10 7 K

Simultaneous chandra and rxte spectroscopy of the microquasar H1743-322 : Clues to disk wind and jet formation from a variable ionized outflow

We observed the bright phase of the 2003 outburst of the Galactic black hole candidate H1743-322 in X-rays simultaneously with Chandra and RXTE on four occasions. The Chandra HETGS spectra reveal narrow, variable (He-like) Fe XXV and (H-like) Fe XXVI resonance absorption lines. In the first observation, the Fe XXVI line has a FWHM of 1800 ? 400 km s-1 and a blueshift of 700 ? 200 km s-1, suggesting that the highly ionized medium is an outflow. Moreover, the Fe XXV line is observed to vary significantly on a timescale of a few hundred seconds in the first observation, which corresponds to the Keplerian orbital period at approximately 104rg (where rg = GM/c2). Our models for the absorption geometry suggest that a combination of changing ionizing flux and geometric effects are required to account for the large changes in line flux observed between observations and that the absorption likely occurs at a radius between 102rg and 104rg for a 10 M? black hole. We suggest that the absorption occurs in an inhomogeneous accretion disk wind. If the wind in H1743-322 has unity filling factor, the highest implied mass outflow rate is 5% of the Eddington mass accretion rate. The observed wind may be a hotter, more ionized version of the Seyfert-like, outflowing warm absorber geometries recently found in the Galactic black holes GX 339-4 and XTE J1650-500. We discuss these findings in the context of ionized Fe absorption lines found in the spectra of other Galactic sources, and connections to warm absorbers, winds and jets in other accreting systems.

Spatial and spectral interpretation of a bright filament in the Cygnus Loop

A comparison is made of optical and UV line intensities and spatial and spectral optical line profiles of a well-defined Cygnus Loop filament with theoretical models. It is found that the sharp filament is due to the tangency to the line of sight of a large, thick sheet of emitting gas. The emitting region associated with the spur is very deep, and there is substantial gradient in shock velocity along the filament. Severe incompleteness of the recombination zone is found at the high-velocity end, and resonance scattering in the emitting region attenuates C IV and other resonance lines, as expected. There is evidence for depletion of Si and Fe relative to other elements. Nonthermal pressure apparently dominates the recombination zone of the filament. New techniques are introduced for determining the completeness of a shock and for determining the preshock density without recourse to the standard density diangostic line ratios.

Far-ultraviolet spectra of fast coronal mass ejections associated with X-class flares

The Ultraviolet Coronagraph Spectrometer (UVCS) on board the Solar and Heliospheric Observatory satellite has observed very fast coronal mass ejections (CMEs) associated with X-class flares. These events show spectral signatures different from those seen in most other CMEs in terms of very rapid disruption of the pre-CME streamer, very high Doppler shifts, and high-temperature plasma visible in the [Fe XVIII] emission line. This paper describes three very similar events on 2002 April 21, July 23, and August 24 associated with X-class flares. We determine the physical parameters of the pre-CME streamers and discuss the geometric and physical nature of the streamer blowouts. In the April 21 event, the hot plasma seen as [Fe XVIII] is not related to the structure seen in [Fe XXI] by the Solar Ultraviolet Measurement of Emitted Radiation (SUMER) instrument at lower heights. It has the form of a rapidly expanding fan, quite likely a current sheet. In the August event, on the other hand, the [Fe XVIII] is probably a bubble of hot plasma formed by reconnection in the wake of the CME. C III emission from the July 23 flare is detected as stray light in the UVCS aperture. It precedes the hard X-ray brightening by about 2 minutes.

Observational Signatures of Particle Acceleration in Supernova Remnants

We evaluate the current status of supernova remnants as the sources of Galactic cosmic rays. We summarize observations of supernova remnants, covering the whole electromagnetic spectrum and describe what these observations tell us about the acceleration processes by high Mach number shock fronts. We discuss the shock modification by cosmic rays, the shape and maximum energy of the cosmic-ray spectrum and the total energy budget of cosmic rays in and surrounding supernova remnants. Additionally, we discuss problems with supernova remnants as main sources of Galactic cosmic rays, as well as alternative sources.