X-ray and optical observations of Nova Muscae 1983 during its nebular stage

The detection of X-rays from Nova Muscae 1983 (discovered on January 18, 1983) constitutes the first detection of X-rays from a classical nova during outburst. X-ray observations were carried out on 1984 April 20 and July 14 when Nova Mus had entered the nebular stage. During both observations no significant flux was observed with the medium energy detectors (2–50 keV). The source was detected with the low energy detector (.04–2 keV) using 3000 Å Lexan and Parlene- N-Aluminium filters; counting rates of (3.4 ± 1.2) × 10³ and (3.7 ± 1.2 × 10^-3 counts/sec were measured with the respective filters. The source was detected again on July 14 with about the same intensity. Either a shocked shell of circumstellar gas emitting 10⁷ thermal bremsstrahlung at 10³⁵ erg/sec intensity or a white dwarf remnant emitting 3.5 × 10⁵ blackbody radiation at 10³⁷ erg/sec luminosity are compatible with the measurements.Spectra taken in the visual spectral range show strong forbidden coronal emission lines of [FeVII] 6085, [FeX] 6374, and as never observed before in such a strength, [FeXIV] 5303 requiring excitation temperatures of 2 × 10⁶ °K.     

LMC X-4: 13.5 s pulsations and an X-ray flare observed by EXOSAT

EXOSAT observed LMC X-4 on November 17/19, 1983 for one 1.4 day binary period during the high state of the 30.5 day cycle. An eclipse with sharp ingress and slow egress was detected with an eclipse angle of 27.1±1.0 dgr. In the medium energy experiment the source showed a hard power law spectrum. Outside eclipse the source was remarkably constant and only one flare was detected on November 17 at 19 UT lasting for about 1 h. The energy spectrum of the source softens considerably during that time and shows an emission line of cold iron. 13.5 sec pulsations are strongly present during the flare and have also been detected during the quiescent period and during several 1 min flares in another EXOSAT LMC X-4 observation on November 22, 1983. A pulse delay time analysis results in the determination of the pulse period (13.5019±0.0002) s and of the semimajor axis of the orbit of the X-ray star (26.0±0.6) It-sec. These results, together with other available information on LMC X-4, allowed to improve the binary parameters. The mass of the neutron star is found to be 1.34 _±0.44 ^0.48 M_o (95% confidence errors).     

Composition of anomalous cosmic rays and implications for the heliosphere

We use energy spectra of anomalous cosmic rays (ACRs) measured with the Cosmic Ray instrument on the Voyager 1 and 2 spacecraft during the period 1994/157-313 to determine several parameters of interest to heliospheric studies. We estimate that the strength of the solar wind termination shock is 2.42 (–0.08, +0.04). We determine the composition of ACRs by estimating their differential energy spectra at the shock and find the following abundance ratios: H/He = 5.6 (–0.5, ⁺0.6), C/He = 0.00048 ± 0.00011, N/He = 0.011 ± 0.001, O/He = 0.075 ± 0.006, and Ne/He = 0.0050 ± 0.0004. We correlate our observations with those of pickup ions to deduce that the long-term ionization rate of neutral nitrogen at 1 AU is 8.3 × 10^–7 s^–1 and that the charge-exchange cross section for neutral N and solar wind protons is 1.0 × 10^–15 cm² at 1.1 keV. We estimate that the neutral C/He ratio in the outer heliosphere is 1.8(–0.7, +0.9) × 10^–5. We also find that heavy ions are preferentially injected into the acceleration process at the termination shock.     

Spectral observation of the composite supernova remnant G 29.7-0.3

The X-ray properties of the supernova remnant G 29.7-0.3 are discussed based on spectral data from the EXOSAT satellite. In the 2 to 10 keV range a featureless power-law spectrum is obtained, the best-fit parameters being: energy spectral index =-0.77, hydrogen column density on the line of sight N_H=2.3.10²² cm^–2. The incident X-ray flux from the source is (3.6±0.1) 10¹¹ erg cm^–2 s^–1 in the 2 to 10 keV range corresponding to an intrinsic luminosity of about 2. 10³⁶ erg s^–1 for a distance of 19 kpc. The source was not seen with the imaging instrument thus constraining the hydrogen column density to be N_H=(3.3 ±0.3) 10²² cm^–2 and the energy spectral index =1.0±0.15. This new observation is consistent with emission by a synchroton nebula presumably fed by an active pulsar. An upper limit of 1.5% for the pulsed fraction in the range of periods 32ms to 10⁴ s has been obtained.     

Simultaneous EXOSAT-IUE observations of NGC 4151

NGC 4151 was observed four times in Nov. 83. The results indicate that: a) there exists a correlation between the X-ray and UV fluxes on the long term; b) the soft X-ray excess between 0.1 and 1 keV is probably steeper than expected from the leaky absorber model by Holt et al (1980); c)the spectral fit to the ME data, after correction for a soft component, yields =1,73±0.27, N_H=(15.2±2.2)×10²² cm^–2, E.W.(Fe line)=0.208±0.084 keV, and does not require a strong overabundance of Fe in the absorber. The relationship between N_H and the strength of the broad emission lines is commented.     

COS-B views on the diffuse galactic gamma-ray emission and some point sources

The correlation between diffuse galactic gamma rays and gas tracers is studied using the final COS-B database and H i and CO surveys covering the entire galactic plane. A good quantitative fit to the gamma rays is obtained, with a small galacto-centric gradient in the gamma-ray emissivity per hydrogen atom. The average ratio of H₂ column density to integrated CO temperature is determined, the best estimate being (2.3 ± 0.3) × 10² molecules cm^–2 (K km s^–1)^–1. Strictly taken, this value is an upper limit. The corresponding mass of molecular hydrogen in the inner galaxy, derived using both 1st and 4th quadrants, is 1.0 × 10⁹ M .The softer gamma-ray spectrum towards the inner galaxy found in previous work can be attributed to a steeper emissivity gradient at low energies and/or to a softer gamma-ray spectrum of the emission distributed like molecular gas. A steeper emissivity gradient at low energies could be related to cosmic-ray spectral variations in the Galaxy, to different distributions of cosmic-ray electrons and nuclei, or to a contribution from discrete sources. A softer spectrum for the emission associated with molecular clouds may be physically related to the clouds themselves (i.e., cosmic-ray spectral variations) or to an associated discrete source distribution.New results on the temporal and spectral characteristics of the high-energy (50 MeV to 5 GeV) gammaray emission from the Vela pulsar are presented. The whole pulsed flux is found to exhibit long-term variability. Five discrete emission regions within the pulsar lightcurve have been identified, with the spectral characteristics and long-term behaviour being different. These characteristics differ significantly from those reported earlier for the Crab pulsar. However, geometrical pulsar models have been proposed (e.g., Morini, 1983; Smith, 1986) which could explain many of these features.     

Instability characteristics of a co-rotating wingtip vortex pair based on bi-global linear stability analysis

The Stereo Particle Image Velocimetry (SPIV) technology is applied to measure the wingtip vortices generated by the up-down symmetrical split winglet. Then, the temporal bi-global Linear Stability Analysis (bi-global LSA) is performed on this nearly equal-strength co-rotating vortex pair, which is composed of an upper vortex (vortex-u) and a down vortex (vortex-d). The results show that the instability eigenvalue spectrum illustrated by (ω_r, ω_i) contains two types of branches: discrete branch and continuous branch. The discrete branch contains the primary branches of vortex-u and vortex-d, the secondary branch of vortex-d and coupled branch, of which all of the eigenvalues are located in the unstable half-plane of ω_i > 0, indicating that the wingtip vortex pair is temporally unstable. By contrast, the eigenvalues of the continuous branch are concentrated on the half-plane of ω_i < 0 and the perturbation modes correspond to the freestream perturbation. In the primary branches of vortex-u and vortex-d, Mode P_u and Mode P_d are the primary perturbation modes, which exhibit the structures enclosed with azimuthal wavenumber m and radial wavenumber n, respectively. Besides, the results of stability curves for vortex-u and vortex-d demonstrate that the instability growth rates of vortex-u are larger than those of vortex-d, and the perturbation energy of Mode P_u is also larger than that of Mode P_d. Moreover, the perturbation energy of Mode P_u is up to 0.02650 and accounts for 33.56% percent in the corresponding branch, thereby indicating that the instability development of wingtip vortex is dominated by Mode P_u. By further investigating the topological structures of Mode P_u and Mode P_d with streamwise wavenumbers, the most unstable perturbation mode with a large azimuthal wavenumber of m = 5–6 is identified, which imposes on the entire core region of vortex-u. This large azimuthal wavenumber perturbation mode can suggest the potential physical-based flow control strategy by manipulating it.     

The primordial Helium-4 abundance determination: systematic effects

By extrapolating to O/H = N/H = 0 the empirical correlations Y–O/H and Y–N/H defined by a relatively large sample of 45 Blue Compact Dwarfs (BCDs), we have obtained a primordial ⁴Helium mass fraction Y _p=0.2443±0.0015 with dY/dZ=2.4±1.0. This result is in excellent agreement with the average Y _p=0.2452±0.0015 determined in the two most metal-deficient BCDs known, I Zw 18 (Z /50) and SBS 0335–052 (Z /41), where the correction for He production is smallest. The quoted error (1) of 1% is statistical and does not include systematic effects. We examine various systematic effects including collisional excitation of hydrogen lines, ionization structure and temperature fluctuation effects, and underlying stellar Hei absorption, and conclude that combining all systematic effects, our Y _p may be underestimated by 2–4%. Taken at face value, our Y _p implies a baryon-to-photon number ratio =(4.7^+1.0 _–0.8)×10^–10 and a baryon mass fraction _b h ² ₁₀₀=0.017±0.005 (2), consistent with the values obtained from deuterium and Cosmic Microwave Background measurements. Correcting Y _p upward by 2–4% would make the agreement even better.     

The variable X-ray spectrum of Cyg XR-1

The variability of the X-ray spectrum of the discrete source Cyg XR-1 (α = 19^h 56^m δ = +35°.1) is reviewed. The variations observed in the energy region accessible to balloon borne detectors (energies greater than 20 keV) can be explained by assuming them to be caused by the eclipsing properties of a binary system. It is suggested that the system is composed of a source of small angular extent having a spectrum similar to that of a black body at approximately 1.5 × 10⁸ K (kT= 12.5 keV) and a non X-radiating companion which eclipses it at intervals of 2.9850 days. The system would be surrounded by an X-radiating plasma whose photon flux between 1 and 100 keV can be approximated by a power law spectrum whose exponent is — 1.7.     

Thermophysics of the planet Mercury

Recent observations of the thermal emission of Mercury at microwave and infrared frequencies now permit a determination of the thermal and electrical properties of the subsurface of the planet. Radar and optical measurements show that the rotation period is 58.65 days, 2/3 of the orbital period. Several negative spectrographic searches verify that the effects of an atmosphere need not be taken into account in computing surface and subsurface temperatures. The observed thermal emission from the planet can then be interpreted from models similar to those developed for study of the Moon but adapted to the peculiar diurnal insolation of Mercury. The observations of Epstein et al. (1970) at 3.3 mm and of Klein (1970a) at 3.75 cm, when interpreted together with recent laboratory measurements of thermal properties of terrestrial and lunar rock powders, indicate that the ratio of electrical to thermal skin depth is 0.9 ± 0.3 times the wavelength in centimeters. Further results of this analysis of the subsurface are: Density = 1.5 ± 0.4 g cm^-3; Electric loss tangent = 0.009 ± 0.004; Inverse thermal inertia = (15 ± 6) × 10^–6 erg^-1 cm² s^1/2 K; Equatorial midnight temperature = 100 ± 15K.The microwave data generally conform to the predictions of the thermophysical models of Mercury developed by Morrison and Sagan (1967), including a suggestion that variations having mean periods of 50 days and 35 days are present in addition to the classical phase effect with period about 116 days. The time-averaged microwave temperature of the planet appears to increase 25 % from millimeter to decimeter wavelengths; this increase suggests that radiation plays an important role in the transport of heat in the subsurface. All of the conclusions of this review indicate that the thermophysical behavior of Mercury closely approximates that expected for the Moon, were it placed in the orbit of Mercury.     

Helium in the terrestrial atmosphere

After a brief historical review of the discovery of helium in the terrestrial atmosphere, the production mechanisms of the isotopes He⁴ and He³ are discussed. Although the radioactive production of He⁴ in the Earth is well understood, some uncertainty still exists for the degassing process leading to an atmospheric influx of (2.5 ±1.5) × 10⁶ atoms cm^–2 s^–1. Different production mechanisms are possible for He³ leading to an influx of (7.5±2.5) atoms cm^–2 s^–1. Observations of helium in the thermosphere show a great variability of this constituent. The different mechanisms proposed to explain the presence of the winter helium bulge are discussed. Since helium ions are present in the topside ionosphere and in the magnetosphere, ionization mechanisms are analyzed. Owing to possible variations and uncertainties in the solar UV flux, the photoionization coefficient is (8±4) × 10^–8 s^–1. Finally, the helium balance between production in the earth and loss into the interplanetary space is discussed with respect to the different processes which can play an effective role.     

Ulysses-Voyager study of energetic particles associated with the intense solar activity of March/June 1991

The intense solar activity centered in March and June 1991 produced some of the largest interplanetary disturbances over the past several solar cycles. For these events the Ulysses EPAC energetic particle observations near 3 AU are compared with those of the Voyager 2 CRS experiment near 35 AU. At Voyager 2 there is a single long-lived event extending over a period of some 6 months while the Ulysses data shows the imprint of individual events as well as the formative stages of the longer lived structure. The average intensity gradient is –17% AU between the 2 spacecraft. At both locations the energy spectra can be represented by an exponential in momentum. The characteristic momentum for protons, (P_o)_H is on the average 4–5 times larger at 35 AU than at 3 AU and there is a significant change in the (P_o)_He/(P_o)_H ratio. However the average H to He ratio is in the range 20–25 for both sets of measurements.     

Pulsars as gamma ray sources: Nebular shocks and magnetospheric gaps

I summarize the results of recent research on the structure and particle acceleration properties of relativistic shock waves in which the magnetic field is transverse to the flow direction in the upstream medium, and whose composition is primarily electrons and positrons with an admixture of heavy ions. Shocks which contain heavy ions that are a minority constituent by number but which carry most of the energy density in the upstream medium put 20% of the flow energy into a nonthermal population of pairs downstream, whose distribution in energy space is N(E) E ^-2, where N(E)dE is the number of particles with energy between E and E+dE. Synchrotron maser activity in the shock front, stimulated by the quasi-coherent gyration of the whole particle population as the plasma flowing into the shock reflects from the magnetic field in the shock front, provides the mechanism of thermalization and non-thermal particle acceleration. The maximum energy achievable by the pairs is _± m _± c ² = m _i c ² ₁/Z _i, where ₁ is the Lorentz factor of the upstream flow and Z _i is the atomic number of the ions. The shock's spatial structure contains a series of overshoots in the magnetic field, regions where the gyrating heavy ions compress the magnetic field to levels in excess of the eventual downstream value. These overshoots provide a new interpretation of the structure of the inner regions of the Crab Nebula, in particular of the wisps, surface brightness enhancements near the pulsar. The wisps appear brighter because the small Larmor radius pairs are compressed and radiate more efficiently in the regions of more intense magnetic field. This interpretation suggests that the structure of the shock terminating the pulsar's wind in the Crab Nebula is spatially resolved, and allows one to measure ₁ 4 × 10⁶, the upstream magnetic field B ₁ to be 3 × 10^-5 Gauss, as well as to show that the total ion flow is 3 × 10³⁴ elementary charges/sec, in good agreement with the total current flow predicted by the early Goldreich and Julian (1969) model. The total pair outflow is shown to be about 5 × 10³⁷ pairs per second, in good agreement with the particle flux required to explain the nebular X—ray source.The energetics of particle acceleration within the magnetospheres of rotation powered pulsars and the consequences for pulsed gamma ray emission are also briefly discussed. The gamma ray luminosity above 100 MeV is shown to scale in proportion to _R ^1/2 , as is in accord with some of the simplest ideas about polar cap models. Models based on acceleration in the outer magnetosphere are also briefly discussed.     

High energy X-ray spectrum of her X-1

Summary On May 8, 1980, we conducted a 90 minute observation on hard X-ray emission (15-200 keV) from Her X-1, using a large area ( 1500 cm²), low background balloon borne X-ray telescope. The energy resolution of the telescope was 17% FWHM at 60 keV. Her X-1 was at binary phase 0.0725 and 2.7 ± 0.5 days after turn on in the 35 day cycle.Average pulsation light curves were obtained by sorting data into 25 equal bins, according to pulse arrival time, modulo the 1.24 sec pulsation period. The width of the main pulse is energy dependent and in the 45–75 keV region about 30% smaller than in the range from 15 to 30 keV.The data have been analyzed by taking the Her X-1 pulse minus background spectrum, where the pulse count rate is defined in a pulse phase interval around the pulse maximum of the 1.24 sec period. The background spectrum was intermittently obtained by a chopping collimator system.A spectral feature is present in emission at an energy of 49.5 (+ 1.5, -3) keV and a FWHM of 18 (+ 6, -3) keV and in absorption at an energy of 29.5 (+ 1.7, -1.5) keV and a FWHM of 17.0 (+ 2.6, -2.8) keV. The intensity of this line feature in emission is (1.8 ± 0.4) photons/cm sec. The line excess in emission over the continuum (with kT = 6.75 (+ 0.2, -0.4) keV) is 7.     

Development of a 1m-normal-incidence-EUV telescope

Astrophysical plasmas at temperatures in the range (0.5–5)×10⁵ K that occur e.g. in interstellar space, in the extended atmospheres around stars of essentially all spectral types, including the numerous late-type stars with low photospheric temperatures, and in the atmospheres of highly evolved stars, can best be studied at extreme ultraviolet wavelengths where they release the bulk of their energy. We report here the current development status of a 1m-normal-incidence-EUV-telescope that will be flown on an ARIES rocket to observe the spectra of nearby stars in the 350 – 700 mm range.     

Energetics of the magnetosphere

Energy flow in various large-scale processes of the Earth's magnetosphere is examined. This energy comes from the solar wind, via the dawn-to-dusk convection electric field, a field established primarily by magnetic merging but with viscous-like boundary interaction as a possible contributor. The convection field passes about 5 × 10¹¹ W to the near-Earth part of the plasma sheet, and also moves the plasma earthward. In addition, 1–3 × 10¹¹ W are given to the complex system of the Birkeland currents: about 4 × 10¹⁰ of this, on the average, goes to parallel acceleration, chiefly of auroral electrons, about 2–3 times that amount to joule heating of the ionosphere, and the rest heats the ring current. The ring current stores energy (mainly as kinetic energy of particles) of the order of 2 × 10¹⁵ J, and this value rises and decays during magnetic storms, on time scales ranging from a fraction of a day to several days. The tail can store comparable amounts as magnetic energy, and appreciable fractions of its energy may be released in substorms, on time scales of tens of minutes. The sporadic power level of such events reaches the order of 3 × 10¹² W. The role of magnetic merging in such releases of magnetic energy is briefly discussed, as is the correlation between properties of the solar wind and magnetospheric power levels.     

Measurement of the Abundance of Helium-3 in the Sun and in the Local Interstellar Cloud with SWICS on Ulysses

The abundance of 3He in the present day local interstellar cloud (LIC) and in the sun has important implications for the study of galactic evolution and for estimating the production of light nuclei in the early universe. Data from the Solar Wind Ion Composition Spectrometer (SWICS) on Ulysses is used to measure the isotopic ratio of helium (3He/4He = ) both in the solar wind and the local interstellar cloud. For the solar wind, the unique high-latitude orbit of Ulysses allows us to study this ratio in the slow and highly dynamic wind in the ecliptic plane as well as the steady high-latitude wind of the polar coronal holes. The 3He+/4He+ ratio in the local cloud is derived from the isotopic ratio of pickup helium measured in the high-speed solar wind. In the LIC the ratio is found to be (2.48 _-0.62 ^+0.68 ) × 10^-4 with the 1- uncertainty resulting almost entirely from statistical error. In the solar wind, is determined with great statistical accuracy but shows systematic differences between fast and slow solar wind streams. The slow wind ratio is variable. Its weighted average value (4.08 ± 0.25) × 10-4 is, within uncertainties, in agreement with the Apollo SWC results. The high wind ratio is less variable but smaller. The average in the fast wind is (3.3 ± 0.3) × 10-4.     

High and medium resolution spectroscopy of the X-ray transient 4U1543-47

Preliminary results of an EXOSAT observation of the transient X-ray source 4U1543-47 are presented. The source was observed in August 1983, during a high state, following a Tenma alert that the source was again active. Results from the GSPC and the LE 1000 l/mm grating are presented. The spectrum is complex, but in the 2–10 keV energy range can be well described by a Comptonised thermal distribution. Extrapolating the same model into the lower energy band of the grating requires an absorption column density equivalent to 2 × 10²¹ H cm². A marked under-abundance of Oxygen and overabundance of Nitrogen, along with a strong, unidentified line feature at 9.8 Å, are necessary to model the grating data.     

Particle measurements on an ESRO satellite (Neutral-1) in a highly eccentric Polar orbit

Conclusion A satellite such as Neutral-1 should be instrumented with magnetometers, plasma detectors, and detectors of energetic particles, and flown to an altitude of some 26 R _E in a high-inclination orbit. It can thus probe regions of the magnetosphere of particular importance but as yet unexplored. It also is in an orbit that offers the optimum variety of phenomena to be explored, with the additional advantage that the characteristics of each phenomenon can be compared one with the other and the interrelation of these phenomena deduced. Such a satellite offers unique opportunities to investigate a multitude of unknown phenomena, such as the origin and energization of the particles that cause auroras and constitute Van Allen radiation. It can also potentially yield data to help solve long-lived problems, viz.: do the particles that cause auroras come from the sun, and how does a ripple in the solar corona ultimately feed energy into the magnetosphere at an average rate of 10¹⁷-10¹⁸ ergs/sec? Someone should fly such a satellite at the earliest opportunity and certainly by sunspot maximum (1969) since the existing satellite and instrumental technology is adequate.     

New Experimental Data and What It Tells Us About the Sources and Acceleration of Cosmic Rays

This paper summarizes new data in several fields of astronomy that relate to the origin and acceleration of cosmic rays in our galaxy and similar nearby galaxies. Data from radio astronomy shows that supernova remnants, both in our galaxy and neighboring galaxies, appear to be the sources of most of the accelerated electrons observed in these galaxies. -ray measurements also reveal several strong sources associated with supernova remnants in our galaxy. These sources have -ray spectra that are suggestive of the acceleration of cosmic-ray nuclei. Cosmic-ray observations from the Voyager and Ulysses spacecraft suggest a source composition that is very similar to the solar composition but with distinctive differences in the ⁴He, ¹²C,¹⁴ N and ²²Ne abundances that are the imprint of giant W-R star nucleosynthesis. Injection effects which depend on the first ionization potential (FIP) of the elements involved are also observed, in a manner similar to the fractionization observed between the solar photosphere and corona and also analogous to the preferential acceleration observed for high FIP elements at the heliospheric solar wind termination shock. Most of the ⁵⁹Ni produced in the nucleosynthesis of Fe peak nuclei just prior to a SN explosion appears to have decayed to ⁵⁹Co before the cosmic rays have been accelerated, suggesting that the⁵⁹ Ni is accelerated at least 10⁵ yr after it is produced. The decay of certain K capture isotopes produced during cosmic-ray propagation has also been observed for the first time. These measurements suggest that re-acceleration after an initial principal acceleration cannot be large. The high energy spectral indices of cosmic-ray nuclei show a significant charge dependent trend with the index of hydrogen being -2.76 and that of Fe -2.61. The escape length dependence of cosmic rays from our galaxy can now be measured up to ~300 GeV nucl^-1 using the Fe sec/Fe ratio. This escape length is P ^-0.05 above 10 GeV nucl^-1 leading to a typical source spectral index of (2.70±0.10) -0.50 = -2.20 for nuclei. This is similar to the source index of -2.3 inferred for electrons within the errors of ±0.1 in the index for both components. Spacecraft measurements in the outer heliosphere suggest that the local cosmic-ray energy density is ~2eV cm^-3 – larger than previously assumed. Gamma-ray measurements of electron bremsstrahlung below 50 MeV from the Comptel experiment on CGRO show that fully 20–30% of this energy is in electrons, several times that previously assumed. New estimates of the amount of matter traversed by cosmic rays using measurements of the B/C ratio are also higher than earlier estimates – this value is now ~10 g cm^-2 at 1 GeV nucl^-1. Thus altogether cosmic rays are energetically a more important component of our galaxy than previously assumed. This has implications both for the types of sources that are capable of accelerating cosmic rays and also for the role that cosmic rays may play in ionizing the diffuse interstellar medium.