Correlation and spectral analysis of daily solar radio flux

Correlation and spectral analysis of solar radio flux density and sunspot number near the maximum of the sunspot cycle has indicated the existence of

1. long period amplitude modulation of the slowly varying component (SVC) of radio emission
2. coronal storage over a period of the order of three solar rotations
3. fast decay (one solar rotation period or less) of gyromagnetic emissions from radio sources
4. shift in location of chromospheric sources compared to those of either the upper corona or the photosphere.

     

X-Ray and microwave observations of active regions

Radio and X-ray observations are presented for three flares which show significant activity for several minutes prior to the main impulsive increase in the hard X-ray flux. The activity in this ‘pre-flash’ phase is investigated using 3.5 to 461 keV X-ray data from the Solar Maximum Mission, 100 to 1000 MHz radio data from Zürich, and 169 MHz radio-heliograph data from Nançay. The major results of this study are as follows:

1. Decimetric pulsations, interpreted as plasma emission at densities of 10⁹–10¹⁰ cm^?3, and soft X-rays are observed before any Hα or hard X-ray increase.
2. Some of the metric type III radio bursts appear close in time to hard X-ray peaks but delayed between 0.5 and 1.5 s, with the shorter delays for the bursts with the higher starting frequencies.
3. The starting frequencies of these type III bursts appear to correlate with the electron temperatures derived from isothermal fits to the hard X-ray spectra. Such a correlation is expected if the particles are released at a constant altitude with an evolving electron distribution. In addition to this effect we find evidence for a downward motion of the acceleration site at the onset of the flash phase.
4. In some cases the earlier type III bursts occurred at a different location, far from the main position during the flash phase.
5. The flash phase is characterized by higher hard X-ray temperatures, more rapid increase in X-ray flux, and higher starting frequency of the coincident type III bursts.

     

On some transient Hα features associated with metric type III bursts

The question of the chromospheric features type III association is reconsidered by using Hα filtergrams both on and off band. A set of 44 metric type III groups, for which an association can be ascertained with a high degree of confidence leads to the following results:

1. The type III's have a dual chromospheric association. Sometimes they are related to a flare, sometimes to a perturbation of a different kind. The latter is seen in absorption in the Hα core and ±0.75 Å away. It is interpreted as a rather dense and cool material in motion in the chromosphere or the low corona. A part of which moves downward, the other upward. The type III's are more closely related to the downward motion.
2. The type III associated absorbing features take place at the border of an active center and along an H_∥ = 0 line. At the present time this appears as the most conspicuous property for marking them off from the great variety of the Hα absorbing features commonly observed on the Sun.
3. Most of the type III associated flares are related to an absorbing feature of the same kind, which appears before the flare itself. This indicates that the initial instability which is responsible for the type III emission is basically the same, whether the bursts are flare associated or not.

Our observations give good evidence that an efficient acceleration of 10–100 keV electrons occur also in the absence of flares. Furthermore the chromospheric perturbation involved in this acceleration is, in many cases, clearly associated to the triggering of a flare. A tentative model is proposed. We assume that in relation with the Hα absorbing feature a stream of fast electrons is accelerated which in turn, under suitable conditions, triggers both the flare and the type III's at the same time.     

Some properties of velocity fields in the solar photosphere

Photoelectric measurements of Doppler shifts of various Fraunhofer lines obtained with the Capri magnetograph were analysed. The height dependence of the supergranular and oscillatory motions, as well as the two dimensional structure of these velocity fields is investigated. The most interesting results are the following:

1. The oscillatory and supergranular motions are still clearly present in very deep photospheric layers as detected e.g. by means of the Ci line at 5380.3 Å.
2. Whereas the vertical motions (both of oscillation and supergranulation) increase with height, the horizontal component of the supergranular flow is found to be decreasing slightly.
3. Aperiodic horizontal motions are observed in the photospheric layers, which are probably connected with the process of excitation of the oscillatory field.
4. There is no simple way of describing the oscillatory field in terms of independently oscillating ‘cells’, since the two-dimensional pattern changes its appearance drastically already in a fraction of one oscillation period.
5. The correlation obtained by previous observers between vertical stationary motions, the chromospheric network and magnetic fields in particular is confirmed.

     

The Alfvén-wave theory of solar flares

Evidence is discussed showing that a representative solar flare event comprises three or more separate but related phenomena requiring separate mechanisms. In particular it is possible to separate the most energetic effect (the interplanetary blast) from the thermal flare and from the rapid acceleration of particles to high energies. The phenomena are related through the magnetic structure characteristic of a composite flare event, being a bipolar surface field with most of its field lines ‘closed’. Of primary importance are helical twists on all scales, starting with the ‘flux rope’ of the spot pair which was fully twisted before it emerged. Subsequent untwisting by the upward propagation of an Alfvén twist wave provides the main flare energy.

1. The interplanetary blast model is based on subsurface, helically twisted flux ropes which erupt to form spots and then transfer their twists and energy by Alfvén-twist waves into the atmospheric magnetic fields. The blast is triggered by the prior-commencing flash phase or by a coronal wave.
2. The thermal flare is explained in terms of Alfvén waves travelling up numerous ‘flux strands’ (Figure 3) which have frayed away from the two flux ropes. The waves originate in interaction (collisions, bending, twisting, rubbing) between subsurface flux strands; the sudden flash is caused by a collision. The classical twin-ribbon flare results from the collision of a flux rope with a tight bunch of S-shaped flux strands.
3. The impulsive acceleration of electrons (hard X-ray, EUV, Hα and radio bursts) is tentatively attributed to magnetic reconnection between fields in two parallel, helically twisted flux strands in the low corona.
4. Flare (Moreton) waves in the corona have the same origin as the interplanetary blast. Sympathetic flares represent only the start of enhanced activity in a flare event already in the slow phase. Filament activation also occurs during the slow phase as twist Alfvén waves store their energy in the atmosphere.
5. Flare ejecta are caused by Alfvén waves moving up flux strands. Surges are attributed to packets of twist Alfvén waves released into bundles of flux strands; the waves become non-linear and drive plasma upwards. Spray-type prominences result from accumulations of Alfvén wave energy in dome-shaped fields; excessive energy density eventually explodes the field.

     

Coherent mechanisms of radio emission and magnetic models of pulsars

This paper is primarily concerned with the questions of models and the mechanisms of radio emission for pulsars, the polarization of this radiation and related topic. For convenience and to provide a more complete picture of the problems involved, a short summary of the data on pulsars is also given. Besides the introduction, the paper contains the following sections:

1. Some Facts about Pulsars.
2. The Astrophysical Nature of Pulsars.
3. Coherent Mechanisms of Radio Emission from Pulsars.
4. Models of Pulsars: Magnetic, Pulsating White Dwarfs and Neutron Stars.
5. The Polarization of the Radio Emission from Pulsars.
6. A Synthesized Model of Pulsars — Magnetic, Pulsating and Rotating Neutron Stars.
7. Concluding Remarks.

     

The photospheric network

Spectroheliograms, obtained in certain Fraunhofer lines with the 82-cm solar image at the Kitt Peak National Observatory, show a bright photospheric network having the following properties:

1. It resembles, but does not coincide with, the chromospheric network, the structure of the photospheric network being finer and more delicate than the relatively coarse structure of the chromospheric network.
2. It is exactly cospatial with the network of non-sunspot photospheric magnetic fields.
3. Its visibility in a given photospheric Fraunhofer line is primarily dependent on the states of ionization and excitation from which the line is formed and secondarily dependent on the Zeemansensitivity of the line-being most visible in low-excitation lines of neutral atoms and least visible in high-excitation lines of singly ionized atoms.

We conclude that these magnetic regions of the solar atmosphere are a few hundred degrees hotter than their surroundings, and that they are visible in white light near the limb as photospheric faculae.     

Microwave emission above steady and moving sunspots

Two-dimensional maps of radio brightness temperature and polarization, computed assuming thermal emission with free-free and gyroresonance absorption, are compared with observations of active region 2502, performed at Westerbork at λ = 6.16 cm during a period of 3 days in June 1980. The computation is done assuming a homogeneous model in the whole field of view (5′ × 5′) and a force-free extrapolation of the photospheric magnetic field observed at MSFC with a resolution of 2″.34. The mean results are the following:

1. A very good agreement is found above the large leading sunspot of the group, assuming a potential extrapolation of the magnetic field and a constant conductive flux in the transition region ranging from 2 × 10⁶ to 10⁷ erg cm^?2s^?1.
2. A strong radio source, associated with a new-born moving sunspot, cannot be ascribed to thermal emission. It is suggested that this source may be due to synchrotron radiation by mildly relativistic electrons accelerated by resistive instabilities occurring in the evolving magnetic configuration. An order-of-magnitude computation of the expected number of accelerated particles seems to confirm this hypothesis.

     

Hard X-rays and associated weak decimetric bursts

In previous attempts to show one-to-one correlation between type III bursts and X-ray spikes, there have been ambiguities as to which of several X-ray spikes are correlated with any given type III burst. Here, we present observations that show clear associations of X-ray bursts with RS type III bursts between 16:46 UT and 16:52 UT on July 9, 1985. The hard X-ray observations were made at energies above 25 keV with HXRBS on SMM and the radio observations were made at 1.63 GHz using the 13.7m Itapetinga antenna in R and L polarization with a time resolution of 3 ms. Detailed comparison between the hard X-ray and radio observations shows:

1. In at least 13 cases we can identify the associated hard X-ray and decimetric RS bursts.
2. On average, the X-ray peaks were delayed from the peak of the RS bursts at 1.6 GHz by ～ 400 ms although a delay as long as 1 s was observed in one case.

One possible explanation of the long delays between the RS bursts and the associated X-ray bursts is that the RS burst is produced at the leading edge of the electron beam, whereas the X-ray burst peaks at the time of arrival of the bulk of the electrons at the high density region at the lower corona and upper chromosphere. Thus, the time comparison must be made between the peak of the radio pulse and the start of the X-ray burst. In that case the delays are consistent with an electron travel time with velocity ～ 0.3 c from the 800 MHz plasma level to the lower corona assuming that the radio emission is at the second harmonic.     

Problems with non-thermal models for the narrow line gamma rays reported from SS 433

The jet/grain model proposed by Ramatyet al. (1984, hereafter abbreviated as RKL) for production of the narrow gamma-ray lines reported from SS433 is examined and shown to be untenable on numerous grounds. Most importantly:

1. The huge Coulomb collisional losses (W _c?2×10⁴¹ erg s^?1) from the jet, which would necessarily accompany non-thermal production of the gamma rays, demands a jet acceleration/collimation process acting over a very long range and with a power at least 10² times the Eddington limit for any stellar object.
2. There is a collisional thick target limit (irrespective of jet mass) to the gamma ray yield per interstellar proton. Consequently, the gamma-ray data demand an improbably high interstellar density (?10⁹ cm^?3).
3. For the grains to be kept cool enough (?3000 K) to survive the heating rateW _c either by radiation or jet expansion would demand a ‘jet’ wider than its length and so inconsistent with narrow lines. In the case of radiative cooling, the resultant IR flux would exceed the observed values by a factor ?10⁴.
4. Light scattered on the jet grain mass required would be highly polarized, contrary to observations, unless the jet was optically thick to grains, again precluding their radiative cooling.
5. To avoid unacceptable precessional broadening of the gamma-ray lines demands an emitting jet length ?0.5 days atv=0.26c. This increases the necessary mass loss rate by a factor ?10 over the values obtained by RKL who assumed a 4-day ‘flare’.
6. The model also predicts rest energy gamma-ray lines which are not observed.

     

On the Hβ, [OIII] lines and continuum variability character in the nucleus of Seyfert galaxy NGC 1275

The radiation fluxes of the NGC 1275 galaxy central region are being observed on the 1.25-m telescope, using a scanning spectrophotometer with the entrance aperture 10″ in three Δλ=80 Å spectral regions: Hβ, 4959+5007 Å [OIII] and continuum. There were 35 nights of observations during 1982–1987. With the time resolution of half an hour 379 measurements were obtained in each spectral region. The analysis of these results shows:

1. The standard deviations of measurements in each spectral region 2–3 times exceed the errors of observations.
2. The radiation flux distribution resembles to normal one only for Hβ line.
3. Two-humps forms of continuum flux distribution curve is like that of radio emission in 8 mm and 2.6 cm wavelengths.
4. Various forms of fluxes distribution curves of Hβ and [OIII] lines permit us to suppose that the location of these lines emission regions near the sources of excitation are different.

     

Observations of limb flares with a soft X-ray telescope

The structure and evolution of 26 limb flares have been observed with a soft X-ray telescope flown on Skylab. The results are:

1. One or more well defined loops were the only structures of flare intensity observed during the rise phase and near flare maximum, except for knots which were close to the resolution of the telescope in size (≈2 arc seconds) and whose structure can therefore not be determined.
2. The flare core features were always sharply defined during the rise phase.
3. For the twenty events which contain loops, the geometry of the structure near maximum was that of a loop in ten cases, a loop with a spike at the top in four cases, a cusp or triangle in four cases, and a cusp combined with a spike in another two cases.
4. Of the fifteen cases in which sufficient data were available to allow us to follow a flare's evolution, five showed no significant geometrical deviation from a loop structure, one displayed little change except for a small scale short-lived perturbation on one side of the loop 10 seconds before a type III radio burst was observed, eight underwent a large scale deformation of the loop or loops on a time scale comparable to that of the flare itself and one double loop event changed in a complex and undetermined manner, with reconnection being one possibility.

Based on observation of the original film, it is suggested that the eight flares which underwent large scale deformations had become unstable to MHD kinks. This implies that these flares occurred in magnetic flux tubes through which significant currents were flowing. It is suggested that the high energy electrons responsible for type III bursts accompanying these flares could have been accelerated by the V x B electric field induced by a small scale short-lived perturbation of parts of a flaring flux tube, similar to the one perturbation which was observed having these characteristics.     

A comparison of He ii 304 Å and He i 10 830 Å spectroheliograms

Spectroheliograms were obtained simultaneously in the He ii 304 Å emission line and the He i 10 830 Å absorption line with an angular resolution of approximately 5″. A negative print of the 304 Å image is matched with a positive print of the 10 830 Å image so that corresponding features of the chromospheric network (including active regions) appear identical in the two images. Differences between these images include the facts that:

1. Disk filaments and limb darkening are strongly visible in the 10 830 Å positive image, but they are weakly visible (as lightenings) in the 304 Å negative image.
2. The contrast between the chromospheric network and the network cell centers is much greater in the 10 830 Å image than in the 304 Å negative image.

These results provide constraints on models of helium line formation in various types of solar features.     

Wave systems in the chromosphere

Observations are reported of two, possibly three, distinct wave systems in the Hα chromosphere.

1. Velocity films show waves propagating predominantly outwards along mottles and fibrils from as close as 2000 km to the network axis at velocities of the order of 70 km s^-1. The line-of-sight component of the velocity amplitude is estimated to be typically 5 km s^-1. The velocities are accompanied by propagating intensity fluctuations. The system is interpreted as one of basically Alfvén waves. Similar waves are observed propagating predominantly outwards along superpenumbral fibrils radiating from a small sunspot.
2. The velocities in the chromospheric granulation undergo fluctuations of an oscillatory character but without any observable horizontal propagation. The intensities show a close correlation with the velocities, maximum intensity occurring about T/4 after maximum downward velocity. The period is variable across the surface (2.5 min upwards). The intensity-velocity correlation is characteristic of a standing compressional wave.
3. Intensity cinefilms at Hα line centre show in places a horizontal drift of the chromospheric granulation pattern at about 12 km s^-1 without any accompanying vertical velocity fluctuations. It is not known whether this is due to a gas stream at sonic velocities, or to a horizontally propagating sound wave.

The Alfvén wave system is shown to make a significant contribution to coronal heating. Whether the velocity fluctuations in the chromospheric granulation also make an important contribution depends on whether there are upwardly propagating or standing waves; this is not yet established despite the intensity-velocity correlation.     

Alfvén waves in the solar atmosphere

We examine the propagation of Alfvén waves in the solar atmosphere. The principal theoretical virtues of this work are: (i) The full wave equation is solved without recourse to the small-wavelength eikonal approximation (ii) The background solar atmosphere is realistic, consisting of an HSRA/VAL representation of the photosphere and chromosphere, a 200 km thick transition region, a model for the upper transition region below a coronal hole (provided by R. Munro), and the Munro-Jackson model of a polar coronal hole. The principal results are:

1. If the wave source is taken to be near the top of the convection zone, where n _H = 5.2 × 10¹⁶ cm^?3, and if B _⊙ = 10.5 G, then the wave Poynting flux exhibits a series of strong resonant peaks at periods downwards from 1.6 hr. The resonant frequencies are in the ratios of the zeroes of J ₀, but depend on B _⊙, and on the density and scale height at the wave source. The longest period peaks may be the most important, because they are nearest to the supergranular periods and to the observed periods near 1 AU, and because they are the broadest in frequency.
2. The Poynting flux in the resonant peaks can be large enough, i.e. P _⊙ ≈ 10⁴–10⁵ erg cm^?2s^?1, to strongly affect the solar wind.
3. ¦δv¦ and ¦δB¦ also display resonant peaks.
4. In the chromosphere and low corona, ¦δv ≈ 7–25 kms^?1 and ¦δB¦ ≈0.3–1.0 G if P _⊙≈10⁴-10⁵ erg cm^?2s^?1.
5. The dependences of ¦δv¦ and ¦δB¦ on height are reduced by finite wavelength effects, except near the wave source where they are enhanced.
6. Near the base, ¦δB¦ ≈ 350–1200 G if P _⊙ ～- 10⁴–10⁵. This means that nonlinear effects may be important, and that some density and vertical velocity fluctuations may be associated with the Alfvén waves.
7. Below the low corona most wave energy is kinetic, except near the base where it becomes mostly magnetic at the resonances.
8. ?₀ < δv ² > v _A or < δB ² > v _A/4π are not good estimators of the energy flux.
9. The Alfvén wave pressure tensor will be important in the transition region only if the magnetic field diverges rapidly. But the Alfvén wave pressure can be important in the coronal hole.

     

Shock remagnetization associated with meteorite impact at planetary surfaces

Shock remagnetization is a significant mode of alteration of the intensity and direction of magnetization in planetary crustal rocks subjected to the dynamic and thermochemical effects associated with meteorite impact. Shock remagnetization will take place almost instantaneously during and following the transient shock episode, and over longer times depending on residual temperature effects associated with shock heating and the production of impact melt. Remagnetization will follow certain demagnetization effects. The following transitions and residual effects will result in remagnetization of planetary crustal material:

1. First order reversible crystallographic transitions in bodycentered cubic iron-nickel alloys.
2. Second order Curie temperature transitions in face-centered cubic iron-nickel alloys.
3. Shock induced uniaxial anisotropy due to magnetoelasstic coupling of magnetic vectors to the shock wave.
4. Shock melting of iron containing silicates.
5. Subsolidus reduction and FeO decomposition.
6. Partial ther moremanence due to post-shock temperature.
7. Total thermoremanence due to post-shock temperature.
8. Production of a superparamagnetic distribution of iron which is sensitive to surface temperature fluctuation.
9. Thermal effects in metal and alloy phases.

Lunar breccia and soil samples are generally more reduced than crystalline rocks and some of th's reduction is subsolidus probably associated with the transient thermal effects due to meteorite impact in teh porous reglith.     

On the birtrate of galactic supernovae

The birthrate of galactic supernovae is estimated in three different ways:

1. on the basis of the historical record (eight events) the mean time interval between supernovae, τ, is considered to be in the range τ=60±40 yr;
2. on the basis of an approximate total of 120 supernovae events in hundreds of other galaxies, considered similar to our own, the interval obtained is in the range τ=70±50 yr; (iii) on the
3. on the basis of the 130 supernovae remnants in our own Galaxy, the interval is estimated to be in the range τ=80±30 yr. The three ranges overlap, and we suggest that 70±35 yr represents a more realistic estimate of the rate than some that have previously been made.

The galactic radio supernovae remnants, and their observed systematic brightness gradients perpendicular to the galactic plane, imply a scale height of about 200 pc for the remnant progenitors, and indicate that the galactic magnetic field's scale-height is about 300 pc. Long standing anomalies associated with (a) the young remnant AD 1006, (b) the galactic loops, and (c) faint remnants, are accounted for by the brightness gradient effect, providing independent, and firm, corroborating evidence for the fundamental validity of the remnant method of deducing the galactic supernova birthrate.     

3C 120 and the surrounding region of sky

Image processing performed on a series of photographs of the superluminal Seyfert galaxy, 3C 120, shows the outer optical disc to consist of fragmented segments generally pointing toward the centre. One long arm of peculiar, separated knots comes off to the W and SW. A peculiar companion is seen along the line of the NW radio jet. In the interior, optical jets are detected which are aligned along the direction of the outer radio jets. A region of the sky 45 ×; 25 degrees around 3C120 is investigated. It is found that:

1. A nebulous filament about 3/4 degree in length points to 3C 120.
2. Hydrogen clouds of redshiftz = ?130 and ?210 km s^?1 are situated at 3 and 1 degrees on either side of 3C 120.
3. Eleven low-surface-brightness galaxies with 4500 <z < 5300 km s^?1 fall within a radius of 8 degrees.
4. Seven quasars withz ? 1.35 and radio fluxesS _b ? 0.3 fall within a radius of 10 degrees.

It is concluded that the concentration of these objects in the vicinity of this unique, active galaxy has a negligible chance of being accidental and that all those objects of diverse redshift are at the same nearby distance. This smaller distance reduces the supposed superluminal motions in 3C 120 to quite precedented ejection velocities.     

A varying cosmological term as a link between cosmology and microphysics

The Weinberg relation (which connects the Hubble constantH to the mass of a typical elementary particle) is an empirical relation hitherto unexplained. I suggest an explanation based on the Zel'dovich energy tensor of vacuum in a Robertson-Walker universe with constant deceleration parameter,q = const. This model leads to

1. the Weinberg relation,
2. a varying cosmological term Λ scaling asH ²,
3. a varying gravitational constantG scaling asH,
4. a matter creation process throughout the universe at the rate 10^?47 g s^?1 cm³,
5. a deceleration parameter in the range -1 to 1/2, which allows a horizon-free universe and makes the lawG/H = constant, consistent with the Viking lander data on the orbit of planet Mars.