Enhanced X-ray Emission Research Articles

A 12CO $J = 1 \hbox{--} 0$) Survey of Molecular Clouds toward the Vela Supernova Remnant with NANTEN

Abstract The molecular distribution toward the whole extent of the Vela SNR has been obtained at a linear resolution of 0.15 pc in 12CO ($J = 1 \hbox{--} 0$) emission with the NANTEN telescope. The CO distribution is generally anti-correlated with the SNR. The X-ray distribution has a sharp boundary toward the CO clouds, especially in the east, suggesting an interaction between them. There is only weak CO emission in the west, and the X-ray emission extends smoothly toward this direction. This indicates that the absence of dense gas probably allowed hot gas to escape freely. The CO clouds are highly filamentary, exhibiting a spatial correlation with regions of optical shocked features on a large scale. In the north of the SNR, enhanced X-ray emission is found toward network-like optical filaments. We suggest that this enhancement is due to the evaporation of molecular gas by shock heating caused by the interaction between the blast wave and the molecular gas. Comparisons with a few simple theoretical models of SNR evolution and expansion indicate that the clouds are mostly pre-existent, are being accelerated, and are evaporating now.

Enhancement of X-ray Emission from a Cooled Kr Gas Jet Irradiated by an Ultrashort KrF Laser Pulse

X-ray emission from a cooled Kr gas jet irradiated by an ultrashort KrF laser pulse (10 mJ in 500 fs) was investigated. When the Kr gas temperature was -100°C, the yields of X-rays with wavelengths of 2–18 and 0.5–0.9 nm were estimated to be 0.53 mJ and 0.44 µJ per pulse, respectively. By decreasing the gas temperature from 20 to -100°C, the yields of the sub-keV and keV X-rays increased by factors of 1.8 and 6.5, respectively. The enhancement of the X-ray yields for the larger clusters formed by gas cooling was caused by the more efficient collisional ionization and excitation brought about by the longer period for which the high local density of the cluster was maintained.

Laboratory simulation of the collision of supernova 1987A with its circumstellar ring nebula

The collision of the remnant of supernova 1987A with its circumstellar ring is laboratory-simulated by using the Gekko XII laser fusion facility at the Institute of Laser Engineering, Osaka University. The pure hydrodynamic approximation was applied using the invariance of the Euler equations. The basic properties of the formation of a young supernova remnant and its collision with the ring are illustrated. Shock wave propagation and plasma flow with triple wavy, vortex ringlike structures were observed using gated X-ray shadowgraphy. The observed hydrodynamic behaviors compare favorably with one-and two-dimensional numerical simulations and further illustrate important qualitative trends. Our experiments suggest the shock reverberation between the ring and the contact discontinuity in the supernova remnant 1987A and resultant oscillation and enhancement of X-ray emission, as well as the emergence of downstream vortex structures.

Distance Limits on the Bright X‐Ray Emission toward the Galactic Center: Evidence for a Very Hot Interstellar Medium in the Galactic X‐Ray Bulge

Observations of the diUuse X-ray background at energies and 1.5 keV show a large region of D3 enhanced emission around the Galactic center. The origin of this X-ray enhancement is not known, but the best candidates are the nearby Loop I superbubble and a Galactic X-ray bulge. To diUerentiate between these two possibilities, the distance scales to the X-rayemitting material along the line of sight must be established. A mosaic of 13 ROSAT PSPC pointings in the direction of l D 337i, b D 4i reveals X-ray shadows in the and 1.5 keV bands cast by a distant molecular cloud complex. Analysis of the 3 shadows indicates that a large fraction (45% ^ 9%) of the observed emission in this direction originates beyond the cloud complex, located at d D 2 kpc. The implied surface brightness of this distant emission source can account for D70% of the enhanced emission away from the absorption trough in the Galac- tic plane. This result indicates that the Loop I bubble cannot be the principal source of the enhanced X-ray emission, and suggests the existence of a bright X-ray source occupying the central region of the Galaxy, with a radial extent of D6 kpc and an X-ray luminosity of D1039 ergs s~1. We examine some simple models of the emission region and compare them to the ROSAT all-sky survey. A thermal origin for the emission implies a plasma temperature of D4 ) 106 K and a total thermal energy in the range of 6¨9 ) 1055 ergs. Subject headings: Galaxy: structureISM: cloudsISM: structureX-rays: ISM

Radial Evolution and Turbulence Characteristics of a Coronal Mass Ejection

We investigate a coronal mass ejection (CME) associated with an X3.9 solar flare that occurred on 1992 June 25. This long-duration event showed a system of large postflare loops at the activity site throughout the period of the enhanced X-ray emission. The drift rate of the metric type IV radio burst observed near the X-ray maximum suggests the speed of the ejecta to be ~350 km s-1 at heights ≤2 solar radii. The solar proton intensities, in the energy range 1-100 MeV observed in the interplanetary medium, show gradual-decay profiles lasting for more than two days and suggest CME-driven acceleration near the Sun. The inference on the spatial and kinematical characteristics of the propagating CME in the inner heliosphere (0.2-1 AU) is primarily based on the interplanetary scintillation observations at 327 MHz, obtained from the Ooty Radio Telescope and the Solar-Terrestrial Environment Laboratory. The scintillation data show the deceleration of propagating disturbance speed, VCME ~ R-0.8, in the interplanetary medium. The speeds obtained from the radio and scintillation measurements also suggest that the coronal shock may not be directly related to the interplanetary shock. The size of the CME in the interplanetary medium seems to follow a simple scaling with distance from the Sun, indicating the pressure balance maintained between the ejecta and the ambient solar wind. The density turbulence spectrum of the plasma carried by the propagating disturbance seems to be flat, Φ ~ κ-2.8, also having a small dissipative scale length, Si(IPD) ≤ 5 km. The spectrum is significantly different from that of high-speed flow from coronal holes and low-speed wind originating above closed-field coronal streamers.

Enhanced X-ray emission in the 1-keV range from a laser-irradiated gas puff target produced using the double-nozzle setup

X-ray emission from a double-stream gas puff target irradiated with a nanosecond Nd:glass laser pulse was studied for the first time. The target was formed by pulsed injection of a high-density gas into a gas cloud by using the double-nozzle setup. This new concept allows a high-density gaseous target to be formed at a relatively large distance from the nozzle output. Enhanced X-ray emission in the 1-keV energy range and a smaller source size were observed as compared to the ordinary gas puff target created by pulsed injection of gas into vacuum. This new approach should be useful in the development of a laser-produced X-ray source for various applications.

X-Ray and Radio Interactions in the Cores of Cooling Flow Clusters

We present high-resolution ROSAT X-ray and radio observations of three cooling flow clusters containing steep-spectrum radio sources at their cores. All three systems exhibit strong signs of interaction between the radio plasma and the hot intracluster medium. Two clusters, A133 and A2626, show enhanced X-ray emission spatially coincident with the radio source, whereas the third cluster, A2052, exhibits a large region of X-ray excess surrounding much of the radio source. Using three-dimensional numerical simulations, we show that a perturbed jet propagating through a cooling flow atmosphere can give rise to amorphous radio morphologies, particularly in the case where the jet was "turned off" and allowed to age passively. In addition, the simulated X-ray surface brightness produced both excesses and deficits as seen observationally.

Cluster effects in deuterium cluster ion implantation on solids

Atomic and nuclear cluster effects of (D3+) were studied by alternative implantation of deuterium cluster ion beam and isolated deuteron (D+) beam on metal targets. The beam energy was adjusted from 10 keV/d to 100 keV/d in experiment. The atomic cluster effect was shown by the enhancement of x-ray emission induced by cluster deuteron. The average ratio of x-ray intensity induced by each cluster deuteron to that induced by each isolated deuteron is about 2.6 in the experimental energy region. The nuclear cluster effect is shown by the difference of D-D fusion rates induced by two kinds of deuterons under the same experimental conditions. The ratio of the D-D fusion rates induced by the two kinds of deuterons is energy dependent.

Multifrequency observations of the interacting galaxy NGC 4922 (UCM 1259 + 2934)

Multifrequency observations of the interacting galaxy NGC 4922 (UCM 1259 + 2934)

An x-ray biplanar photodiode and the x-ray emission from magnetically confined laser produced plasma

Development of a single and multichannel biplanar vacuum photodiode for x-ray detection is reported, which has been used to study the x-ray emission from laser produced plasma expanding across an externally applied magnetic field. Two to three times enhancement in x-ray emission has been observed which was found correlated with decrease in size of the x-ray emitting plasma plume (expansion velocity of plasma). Experimental observations were found in close agreement with the analytical model based on an increase in plasma density as a result of plasma confinement in magnetic field. Temporal evolution of x-ray emission indicates that recombination radiation seems to be playing an important role in x-ray enhancement.

Some studies on picosecond laser produced plasma expanding across a uniform external magnetic field

Some characteristics of the picosecond laser produced plasma expanding across an externally applied magnetic field (0.6T) have been reported. Two to three times enhancement in X-ray emission from copper plasma has been observed for the laser intensity range ∼5 X 1011 to 5 X 1012 W/cm2. The X-ray yield has been found to increase with an increase in the magnetic field intensity. Enhancement in X-ray emission is correlated with confinement of expanding plasma either in external magnetic field or in high ambient gas pressure. Generation of some highfrequency instability and fast ions was also observed in the plasma along with bouncing of plasma near the β = 1 surface where kinetic pressure of plasma equals magnetic pressure.

New data on space and time scales of relativistic runaway electron avalanche for thunderstorm environment: Monte Carlo calculations

Time and space scales of a relativistic runaway electron avalanche (RREA) t i and l i for a thunderstorm environment were calculated by means of a simplified MC code and a standard VNIIEF MC code ELISA, with all possible kinds of elementary interactions being taken into account. The effect of elastic scattering on RREA was analyzed. New values of t i and l i were used to simulate the enhancement of X-ray emission inside thunderstorm clouds due to energization and avalanche multiplication of cosmic-ray produced electrons. Results appeared to be consistent with published data obtained during flight observations inside thunderclouds.

Behavior of expanding laser produced plasma in a magnetic field

Characteristics of a laser produced plasma expanding across an externally applied magnetic field (0.6 T) have been reported. Two to three times enhancement in x-ray emission from copper plasma has been observed for the laser intensity range ∼5 × 1011–5 × 1012 W/cm2. The x-ray yield has been found to increase with an increase in the magnetic field intensity. Enhancement in x-ray emission is correlated with confinement of an expanding plasma in an external magnetic field. Generation of fluid instability has been found at the expanding plasma surfaces where the kinetic pressure of the plasma equals the magnetic pressure.

Supernova Remnants in the Magellanic Clouds. I. The Colliding Remnants DEM L316

The Large Magellanic Cloud (LMC) supernova remnant (SNR) DEM L316 is of considerable interest, as it shows two overlapping shells at radio and optical wavelengths. This morphology suggests that DEM L316 is in fact two SNRs, which may or may not be spatially connected. We have observed the DEM L316 remnants at optical, radio, and X-ray wavelengths in order to address the question of whether the SNRs are interacting, and if so, whether a tunnel might have formed between the remnants, allowing them to equilibrate. Besides the connecting shell morphologies at optical and radio wavelengths, our observations show enhanced [O III] emission at the juncture between the shells, enhanced X-ray emission from one shell at that juncture, and a change in the structure of the magnetic field near the interaction region. These factors strongly imply that the two remnants are indeed colliding. In addition, we have done a detailed study on the physical properties of the remnants, including an examination of thermal and kinetic energies and of the balance of thermal and magnetic pressures.

Corona(e) of AR Lacertae. II. The Spatial Structure

The X-ray light curves in the 0.4-1.5 keV and 2-7 keV bands of the RS CVn binary AR Lacertae observed on 1993 June 1-3 over one full orbital cycle with the ASCA satellite have been used to map the spatial structure of AR Lac's coronae. We find that both stars are X-ray active, that the corona of the K-type secondary star appears to be hotter than that of the G-type primary star, that X-ray emission is concentrated on the sides of the stars facing each other, and that there are compact and well-localized regions of enhanced X-ray emission with heights much smaller than the stellar radii. In one class of solutions there are additional extended regions with dimensions similar to or greater then the radii of the underlying stars which may be structures that interconnect the two stars. There are also other acceptable models without extended structures, however our analysis indicates that solutions with extended sources are more probable. Also, about 50% of the X-ray emission is unmodulated and could come from either an extended halo region, from the poles of the larger K star, or from other symmetric or uneclipsed structures in the orbital plane. We compare the coronal structures inferred from the ASCA observations with those inferred using the same technique from an EXOSAT observation of AR Lac made in 1984 and find that there are substantial differences between the coronal structures at these two epochs. For the solution with extended material in the orbital plane, we have derived the rough physical parameters for the X-ray-emitting plasma, using the derived information on the spatial sizes of the various spatial components together with information about the emission measure and temperatures obtained from a simple spectral analysis of the ASCA data.

Ultraviolet prepulse for enhanced x-ray emission and brightness from droplet-target laser plasmas

We show that an ultraviolet prepulse significantly enhances the water-window x-ray emission and brightness for a droplet-target laser plasma. By combining a 65 mJ, 120 ps, λ=532 nm main pulse with an up to 3 mJ prepulse, the emitted x-ray photon flux may be increased more than eight times. The resulting C VI λ=3.37 nm line emission is more than 3×1012 photons/sr⋅pulse, corresponding to a conversion efficiency above 3%/line. The integrated spectral brightness is increased two times and is found to reach its maximum for different prepulse parameters than those resulting in maximum photon flux.

Enhanced x-ray emission from the valence states to the 1s and 2s levels in metallic Mo and several Mo compounds

The influence of solid and chemical effects on photo-induced x-ray transitions from the valence states was investigated by means of high-resolution x-ray diffractometry. The study was devoted to metallic Mo and , and compounds. A significant enhancement of the emission rate of the 4d - 1s and 4d - 2s quadrupole-allowed transitions was found for the targets studied. The change of the transition probability is interpreted as being due to the mixing of the 4d states with p character orbitals. Further, the effect of exchange interaction between the 4p core level and the

ASCA X-Ray Observations of the Vela Pulsar Jet

AbstractAn X-ray jet-like outflow, beginning at the Vela pulsar and extending about seven parsecs along the pulsar spin axis direction has recently been discovered (Markwardt & Ögelman 1995). We present data obtained by the X-ray ASCA satellite which confirms the enhanced X-ray emission at the jet head and discuss the allowable spectral models. The jet parameters are updated according to the combined ROSAT and ASCA results.

ROSAT Observations of X-ray Emissions from Jupiter During the Impact of Comet Shoemaker-Levy 9

Röntgensatellit (ROSAT) observations made shortly before and during the collision of comet Shoemaker-Levy 9 with Jupiter show enhanced x-ray emissions from the planet's northern high latitudes. These emissions, which occur at System III longitudes where intensity enhancements have previously been observed in Jupiter's ultraviolet aurora, appear to be associated with the comet fragment impacts in Jupiter's southern hemisphere and may represent brightenings of the jovian x-ray aurora caused either by the fragment impacts themselves or by the passage of the fragments and associated dust clouds through Jupiter's inner magnetosphere.

Mass concentrations associated with extended X-ray sources in the core of the Coma cluster

Using a deep (approx. 20,200 s) ROSAT Position Sensitive Proportional Counter (PSPC) image we have examined the central region of the Coma cluster. Two extended regions of enhanced X-ray emission are found, centered at the positions of the brightest elliptical galaxies in the cluster: NGC 4874 and NGC 4889. Spectral analysis of the sources reveals no evidence of any difference between the spectra of these sources and that of the surrounding cluster emission. We assume that the enhancement in the X-ray surface brightness results from gas density enhancements and also that the underlying mass concentrations lie either at the cluster center or 1 core radius out of the center (420 kpc). With these assumptions, we derive total masses of 1.2 x 10(exp 13) - 1.6 x 10(exp 13), and 0.9 x 10(exp 13) - 1.8 x 10(exp 13) Solar mass within 2 min (80 kpc) of NGC 4874 and NGC 4889, respectively, assuming a Hubble constant H(sub 0) = 50 km/s/Mpc. Corresponding mass-to-light ratios for the galaxies are 30-40 and 25-50 in solar units, increasing at larger radii and approaching the values derived for the entire cluster at distances of more than approximately 150 kpc from the galaxies.