Low frequency flickering of TT arietis: Hard and soft X-ray emission region

Using archival ASCA observations of TT Arietis, X-ray energy spectra and power spectra of the intensity time series are presented for the first time. The energy spectra are well-fitted by a two continuum plasma emission model with temperatures 1 keV and 10 keV. A coherent feature at 0.643 mHz appeared in the power spectra during the observation.     

Time Evolution of low-Frequency Periodicities in Cosmic ray Intensity

The long-time series of daily means of cosmic-ray intensity observed by four neutron monitors at different cutoff rigidities (Calgary, Climax, Lomnický tít and Huancayo/Haleakala) were analyzed by means of the wavelet transform method in the period range 60 to 1000 days. The contributions of the time evolution of three quasi-periodic cosmic-ray signals (150 d, 1.3 yr and 1.7 yr) to the global one are obtained. While the 1.7-yr quasi-periodicity, the most remarkable one in the studied interval, strongly contributes to the cosmic ray intensity profile of solar cycle 21 (particularly in 1982), the 1.3-yr one, which is better correlated with the same periodicity of the interplanetary magnetic field strength, is present as a characteristic feature for the decreasing phases of the cycles 20 and 22. Transitions between these quasi-periodicities are seen in the wavelet power spectra plots. Obtained results support the claimed difference in the solar activity evolution during odd and even solar activity cycles.     

The baryon-symmetric domain cosmology and the cosmic X-ray background

The baryon-symmetric domain cosmology (BSDC) of Steckeret al. (1971) have explained the diffuse -ray background. However, evidence has shown that active galactic nuclei (AGNs) are likely contributors to the diffuse -ray background, so there are some problems with the original formulations. We have reviewed the original formulations and have modified the expressions for the matter temperature and the redshifts at which the cosmic radiation from the BSDC becomes significantly absorbed. In this way, we show that the cosmic radiation from the BSDC agrees remarkably with the cosmic X-ray background from 1 keV to 100 keV. We have also shown that AGNs contribute significantly to the cosmic background beyond 100 keV. Therefore, we have arrived at a consistent model in which the BSDC model and AGN model together can explain the cosmic background from 1 keV to 1 MeV.     

Observations and analysis of CF Tuc

RecentUBV photometry of the RS CVn binary CF Tuc is discussed and analysed. If we combine the results with previously published spectroscopy we find radii of 1.63R for the hotter (6000 K) and 3.11R for the cooler (4500 K) component; both stars having a mass of about 1.3M . The distance to the system is put at 86±15 pc.Though the photometric data is incomplete in the coverage of some regions out of the minima, there is no significant evidence of the wave-type distortions — a known hallmark of RS CVn stars — and the data can be modeled by a standard eclipsing binary system in which the statistical test of goodness-of-fit (²) produces quite acceptable values for reasonable estimates of observational accuracy (0.01 mag). We, therefore, have no need to postulate any additional photometric complications, and feel entitled to some confidence in the reliability of the derived parameter set.     

10–100 keV electron acceleration and emission from solar flares

We present an analysis of spacecraft observations of non-thermal X-rays and escaping electrons for 5 selected small solar flares in 1967. OSO-3 multi-channel energetic X-ray measurements during the non-thermal component of the solar flare X-ray bursts are used to derive the parent electron spectrum and emission measure. IMP-4 and Explorer-35 observations of > 22 keV and > 45 keV electrons in the interplanetary medium after the flares provide a measure of the total number and spectrum of the escaping particles. The ratio of electron energy loss due to collisions with the ambient solar flare gas to the energy loss due to bremsstrahlung is derived. The total energy loss due to collisions is then computed from the integrated bremsstrahlung energy loss during the non-thermal X-ray burst. For > 22 keV flare electrons the total energy loss due to collisions is found to be 10⁴ times greater than the bremsstrahlung energy loss and 10² times greater than the energy loss due to escaping electrons. Therefore the escape of electrons into the interplanetary medium is a negligible energetic electron loss mechanism and cannot be a substantial factor in the observed decay of the non-thermal X-ray burst for these solar flares.We present a picture of electron acceleration, energy loss and escape consistent with previous observations of an inverse relationship between rise and decay times of the non-thermal X-ray burst and X-ray energy. In this picture the acceleration of electrons occurs throughout the 10–100 sec duration of the non-thermal X-ray burst and determines the time profile of the burst. The average energy of the accelerated electrons first rises and then falls through the burst. Collisions with the ambient gas provide the dominant energetic electron loss mechanism with a loss time of 1 sec. This picture is consistent with the ratio of the total number of energetic electrons accelerated in the flare to the maximum instantaneous number of electrons in the flare region. Typical values for the parameters derived from the X-ray and electron observations are: total energy in > 22 keV electrons total energy lost by collisions = 10^28–29 erg, total number of electrons accelerated above 22 keV = 10³⁶, total energy lost by non-thermal bremsstrahlung = 10²⁴erg, total energy lost in escaping > 22 keV electrons = 10²⁶erg, total number of > 22 keV electrons escaping = 10^33–34.The total energy in electrons accelerated above 22 keV is comparable to the energy in the optical or quasi-thermal flare, implying a flare mechanism with particle acceleration as one of the dominant modes of energy dissipation.The overall efficiency for electron escape into the interplanetary medium is 0.1–1% for these flares, and the spectrum of escaping electrons is found to be substantially harder than the X-ray producing electrons.Currently at Tokyo Astronomical Observatory, Mitaka, Tokyo, Japan.     

Electron acceleration in solar flares

We present observations of an intense solar flare hard X-ray burst on 1980 June 27, made with a balloon-borne array of liquid nitrogen-cooled germanium detectors which provided unprecedented spectral resolution (1 keV FWHM). The hard X-ray spectra throughout the impulsive phase burst fitted well to a double power-law form, and emission from an isothermal 10⁸–10⁹K plasma can be specifically excluded. The temporal variations of the spectrum indicate that the hard X-ray burst is made up of two superposed components: individual spikes lasting 3–15 s, whch have a hard spectrum and a break energy of 30–65 keV; and a slowly varying component characterized by a soft spectrum with a constant low-energy slope and a break energy which increases from 25 keV to 100 keV through the event. The double power-law shape indicates that acceleration by DC electric fields parallel to the magnetic field, similar to that occurring in the Earth's auroral zone, may be the source of the energetic electrons which produce the hard X-ray emission. The total potential drop required for flares is typically 10² kV compared to 10 kV for auroral substorms.     

A search for soft X-ray emission from stellar sources

With the soft X-ray detector (0.2–0.284 keV) aboard the Astronomical Netherlands Satellite (ANS) we have searched for X-ray emission from hot star coronae and peculiar stars. On Sirius ( CMa) and Capella ( Aur) X-ray emission has been measured at 6 and 5 level, respectively, above background. In all other cases the search revealed no evidence for soft X-ray emission. Upper limits to the luminosities of about 25 star coronae (main-sequence stars, (sub)giants, and supergiants) and of 4 peculiar stars ( Sco, Lyr, P Cyg, and Car) have been obtained.Paper presented at the COSPAR/IAU Symposium on Fast Transients in X-and Gamma-Rays, held at Varna, Bulgaria, 29–31 May, 1975.     

A GRB model satisfying stringent observational constraints

The temporal behavior of GRBs is quantified using a power spectrum analysis. The power spectrum of great variety of GRBs is well represented by the simple ^–2 behavior. We then study a cosmological GRB model in which relativistic flows interact with dense radiation fields. This mechanism in the densest stellar regions known to exist, surprisingly yields the correct temporal behavior. Other characteristics are also reproduced, including the duration bimodality and the hardness-duration distribution.     

Periodicity in filamentary activity

This paper presents the results of the study on the periodicity in filament activity. The spectral analysis of the number of filaments shows a basic period at 141 (10.5 yr), at 138 (10.3 yr), and at 144 (10.7 yr) Carrington rotation in the northern and southern hemisphere, respectively.The time series concerning the index of filament activity shows also a typical period at 135 Carrington rotation (10.1 yr) at 144 Carrington rotation (10.7 yr) and at 133 Carrington rotation (9.9 yr), respectively, in the northern and southern hemisphere.The power spectrum analysis of the time series of the filamentary activity in the short-term also yields less pronounced but still noticeable peaks which are statistically significant.     

Low noise beam-lead diode mixer for the 3 mm radio astronomical receiver at the metsähovi radio research station

A 3 mm low noise beam-lead Schottky diode mixer has been developed. At cryogenic temperatures the conversion loss is 6.3 dB, and the DSB mixer noise temperature is 75 K, respectively. The mixer was installed into the cooled receiver for radioastronomical observations at the Metsähovi 13.7-m radio telescope. Total DSB noise temperature of the cooled receiver with an ultra low noise HEMT IF amplifier was 110 K at 103 GHz. The tuning range of the mixer mount was from 70 GHz to 115 GHz.     

In situ acceleration and gradients of charged particles in the outer solar system observed by the voyager spacecraft

The probable connection between cosmic rays and the electromagnetic state of the interplanetary medium was recognized by Hannes Alfvén as early as 1949 (Alfvén, 1949, 1950); he pointed out that the properties of cosmic rays necessitate a mechanism, external to Earth but within the solar system, capable of accelerating particles to extremely high energies. In advocating the view of local origin for part of the cosmic-ray spectrum, Alfvén and his colleagues developed a very general type of acceleration mechanism called magnetic pumping. The unique data set of the two Voyagers extends over an entire decade (1977–1987) and is most suitable to explore the problem of acceleration of charged particles in the heliosphere. The energy coverage of the Low Energy Charged Particle (LECP) experiment covers the range 30 keV to several hundred MeV for ions and 22 keV to several MeV for electrons. Selected observations of interplanetary acceleration events from 1 to 25 AU are presented and reviewed. These show frequent acceleration of ions to several tens of MeV in association with shocks; highest energies (220 MeV oxygen) were measured in the near-perpendicular ( _Bn 87.5°) shock of January 5, 1978 at 1.9 AU, where electron acceleration was also observed. Examples of ion acceleration in association with corotating interaction regions are presented and discussed. It is shown that shock structures have profound effects on high-energy (70 MeV) cosmic rays, especially during solar minimum, when a negative latitudinal gradient was observed after early 1985 at all energies from 70 MeV down to 30 keV. By early 1987, most shock acceleration activity in the outer heliosphere (25 to 30 AU) had ceased both in the ecliptic (Voyager-2) and at higher (30°) ecliptic latitudes (Voyager-1). The totality of observations demonstrate that local acceleration to a few hundred MeV, and as high as a few GeV is continually present throughout the heliosphere. It should be noted that in 1954 when Alfvén suggested local acceleration and containment of cosmic rays within the solar system, no one treated his suggestion seriously, at any energy. The observations reviewed in this paper illustrate once more Alfvén's remarkable prescience and demonstrate how unwise it is to dismiss his ideas.Paper dedicated to Professor Hannes Alfvén on the occasion of his 80th birthday, 30 May 1988.     

Motion of Spinning Particles in Gravitational Fields

A non-LTE study of the Type IIb supernova 1993J in the galaxy M81 taking into account nonthermal ionization and line blocking effects is carried out. Hydrodynamical models and theoretical spectra clearly show that nonthermal ionization and excitation dominate after the second maximum, at day 30, and play a decisive role in reproducing both the smooth tail of the light curve and the emergence of helium lines in the spectrum, similar to those observed. Based on our model of supernova 1993J, we predict that the light curves of Type Ib supernovae should be subject to nonthermal ionization and excitation at earlier times than even those for supernova 1993J. In our model, the outburst of supernova 1993J is interpreted as the explosion of a 4 M red supergiant, which underwent core collapse and left a neutron star in a binary system. The progenitor is supposed to have a helium core mass of 3 M, corresponding to a 13 M main-sequence star. Supernova 1993J adds evidence to the scenario that Type Ib supernovae originate from moderately massive stars on the main sequence that have lost their hydrogen envelopes in interacting binary systems.     

An analysis of the longitudinal distribution of gamma rays from SAS-II data

An analysis of the longitudinal distribution of gamma rays from SAS-II data has been carried out using the available information on the gas distribution in the Galaxy. The overall distribution of cosmic rays in the galactic plane can be represented by an exponential function in galactocentric distance with a scale length of 8 kpc upto the solar circle and 10 kpc beyond. There is no evidence for a large gradient of the cosmic ray intensity in the outer parts of the Galaxy. The local emissivities of gamma rays in the energy regionsE >100 MeV and 35 MeV<E <100 MeV are (1.73±0.27)×10^–25 photon/(cm³ s n_H) and (2.40±0.41)×10^–25 photon/(cm³ s n_H) respectively. The contribution of °-decay gamma rays is 80% forE >100 MeV and 20% at lower energies. The electron spectrum required by this analysis has a power law spectral index of about –2.7 below a few hundred MeV. The observed gas distribution towards the galactic centre would predict a gamma-ray flux larger than observed. It is suggested that the molecular gas in the central region may be in the form of dense coudlets, in which low evergy cosmic rays do not penetrate; in this case the centre should be seen as a strong source only at high energies. An analysis of the radio sky survey map of the Galaxy at 408 MHz shows thatB varies with a scale-length of 40 kpc; no significance can be attached to the apparent deviation from the equipartition of energy densities between cosmic rays and magnetic field. The derived local emissivity is (1.46±0.28)×10^–40 W/((m³ Hz), which corresponds toB 5 G. The surface brightness of radio and gamma-ray emissions in the Galaxy decreases from the centre with scale-lengths 6 kpc and 7 kpc respectively. No positive correlation can be noticed with either co-rotation radius or pattern speed, when compared with external spiral galaxies.     

Compttonization-softening and the hard X-ray spectrum of CYG X-1

The Comptonization-softening of very hard X-ray photons withEm ₀ c ² in the cold electron gas is discussed. The frequency diffusion equation for Comptonization of hard X-rays has been derived to the zero-temperature approximation. By use of this equation, and under the assumption of pair-annihilation origin of hard X-rays, we calculated the energy spectrum withE>80 keV, for Cyg X-1, which is in good fit with the observation. The high-energy edge 400 keV of the observed spectrum and the small bump in the range 100–200 keV also can be explained by this way.     

On the evolution of low mas binary systems

The evolution of parameters of close binary systems containing a red dwarf (with mass loss) and a condensed star is investigated. The mass loss from the system and asynchronism of the red dwarf rotation are taken into consideration. The calculations show that if the initial mass ratioq ₀2 then during 10⁷ yr the instability of mass loss process arises, and a bright X-ray source forms with luminosity close to the Eddington one. Ifq ₀>2 then during the mass loss phase the bright X-ray source arises twice. The models explain the existence of the forbidden interval of orbital periods and the absence of systems with periods less than 80 min.     

Spatial development of X-ray emission during the impulsive phase of a solar flare

The flare of 11 November, 1980, 1725 UT occurred in a magnetically complex region. It was preceded by some ten minutes by a gradual flare originating over the magnetic inversion line, close to a small sunspot. This seems to have triggered the main flare (at 70 000 km distance) which originated between a large sunspot and the inversion line. The main flare started at 172320 UT with a slight enhancement of hard X-rays (E > 30 keV) accompanied by the formation of a dark loop between two H bright ribbons. In 3–8 keV X-rays a southward expansion started at the same time, with - 500 km s ^–1. At the same time a surge-like expansion started. It was observable slightly later in H, with southward velocities of 200 km s^–1. The dark H loop dissolved at 1724 UT at which time several impulsive phenomena started such as a complex of hard X-ray bursts localized in a small area. At the end of the impulsive phase at 172540 UT, a coronal explosion occurred directed southward with an initial expansion velocity of 1800 km s^–1, decreasing in 40 s to 500 km s^–1.Now at Fokker Aircraft Industries, Schiphol, The Netherlands.     

Gamma-Ray Bursts: Should cosmologists care?

Gamma-Ray Burst (GRB) locations are distributed isotropically on the sky, but the intensity distribution of the bursts seems clearly incompatible with spatial homogeneity. Of the scenarios that attempt to provide an explanation, there are two that enjoy current popularity: (1) GRBs are produced by high-velocity neutron stars that have formed an extended (100 kpc) spherical halo or corona around our galaxy. (2) The bursters are at cosmological distances, with redshifts near unity for the weaker events. The major evidence used to argue for or against each of these scenarios remains inconclusive. Assuming, not unreasonably, that the cosmological scenario is correct, one can discuss the advantages and disadvantages of studying GRBs as opposed to other objects at moderate redshift. We find that the advantages of GRBs-high intensity, penetrating radiation, rapid variability, and no expected source evolution-are offset by observational difficulties pertaining to the extraction of cosmological information from GRB data. If the cosmological scenario proves to be correct and if the observational difficulties are overcome, then cosmologists certainly should care.     

Short-Term Periodicities in the Time Series of Solar Radio Emissions at Different Solar Altitudes

A spectral analysis of the time series of daily values of 12 parameters, namely, ten solar radio emissions in the range 275–1755 MHz, 2800 MHz solar radio flux, and sunspot numbers for six continuous intervals of 132 values each during June 1997–July 1999 showed considerable differences from one interval to the next, indicating a nonstationary nature. A 27-day periodicity was noticed in Interval 2 (26.8 days), 3 (27.0 days), 5 (25.5 days), 6 (27.0 days). Other periodicities were near 11.4, 12.3, 13.3, 14.5, 15.5, 16.5, 35, 40, 50–70 days. Periodicities were very similar in a large vertical span of the coronal region corresponding to 670–1755 MHz. Above this region, the homogeneity disappeared. Below this region, there were complications and distortions due to localized solar surface phenomena.     

Eruption of a helically twisted prominence

In this paper we analyze the eruption of a prominence, characterized by a helical-like structure and by a non-linear rising motion. We approximated the prominence as a cylindrical curved flux tube and estimated the behaviour of several geometrical parameters during the activation and the eruption phases. We determined that, at the onset of the activation, the number N of turns of a magnetic field line over the whole length of the prominence was 5.0, while the value of the ratio P/r ₀ between the pitch of the magnetic field lines and the prominence width was 0.45. These values are in good agreement with those predicted by the kink-mode instability. Moreover, we found a decrease of the total twist of one helical thread from 10 to 2 during the prominence eruption, indicating a relaxation of the magnetic field towards a less twisted configuration. We conclude that the prominence was initially destabilized by the kink-mode instability and, not succeeding in finding a new equilibrium configuration, it erupted.     

The fundamental role of giant comets in earth history

We discuss some fundamental aspects of Earth history as predicted by what has come to be called coherent rather than stochastic catastrophism. The latter essentially seeks to provide an understanding of terrestrial evolution in terms of occasional kilometre-plus impactors from the asteroid belt whereas the former recognises a far more complex extraterrestrial regime arising from the streams of sub-kilometre and kilometre-plus debris due to the disintegration of successive giant comets in sub-Jovian orbits. Periodicities of 15 Myr during the later Phanerozoic (i.e. 250 to 0 Myr BP) and 200 yr during the Holocene (i.e. 10,000 to 0 yr 1313) are likely fundamental signatures in the terrestrial record relating to the action of past and present giant cornets respectively.