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.     

Structure and evolution of solar radio bursts at 26.4 MHz

Two dimensional source brightness distributions at 26.4 MHz for solar bursts of spectral type II, III, IV, and V are derived from observations with a multiple-baseline, time-sharing interferometer system. It was designed explicitly to study the large angle (40 halo) component of low frequency solar bursts first reported by Weiss and Sheridan (1962). Thirty-two bursts occurring in the interval of June–August, 1975, were fit with a circular gaussian core and an elliptical gaussian halo component. Half-power halo diameters (E-W×N-S) averaged 30×28 for type III bursts and 42×27, 28×37, 30×25 for type V, II and IV bursts respectively. Typical core sizes fell in the range of 10±4 giving 31 halo to core size ratio. All burst types were found to have some large angle structure: the specific intensity was 10% compared to the core but the total power in each component was comparable. Two processes for producing the core-halo structure of type III bursts are compared: scattering and refraction of a point source and refraction from many sources over an extended region. It is concluded that the core can be explained by either model but the halo is more consistent with emission from an extended source region of 40° in longitude.     

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.     

Hα and radio observations of LSI+61o303

Quasi simultaneous H and radio observations of LSI+61^o303 during August-September 1993 are presented. The radio data show that during the studied epoch the outburst has peaked at radio phase 0.6, at level100 mJy. No significant variations in the H profile at phases 0.5 to 0.65 have been detected. A remarkable increase of the EW and FWHM of the H blue peak is observed at radio phase 0.23. Possible reasons are considered.     

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 comparative spectra of cosmic-ray protons and helium nuclei

We have re-examined and extended the measurements of the primary cosmic ray proton and helium nuclei intensities in the range from a few MeV nuc^–1 to 100 GeV nuc^–1 using a considerable body of recently published data. The differential spectra obtained from this data are determined as a function of both energy and rigidity. The exponents of the energy spectra of both protons and helium nuclei are found to be different at the same energy/nucleon and to increase with increasing energy between 1 and 100 GeV nuc^–1 reaching a value=–2.70 at higher energies and in addition, theP/He ratio changes from a value 5 at 1 GeV nuc^–1 and below to a value 30 at 100 GeV nuc^–1. On a rigidity representation the spectral exponent for each species is nearly identical and remains virtually constant above several GV at a value of –2.70, and in addition, theP/He ratio is also a constant 7 above 3 GeV. The changingP/He ratio and spectral exponent on an energy representation occur at energies well above those at which interplanetary modulation effects or interstellar ionization energy loss effects can significantly affect the spectra. In effect by comparing energy spectra and rigidity spectra in the intermediate energy range above the point where solar modulation effects and interstellar energy loss effects are important, but in the range where there are significant differences between energy and rigidity spectra, we deduce that the cosmic ray source spectra are effectively rigidity spectra. This fact has important implications regarding the mechanism of acceleration of this radiation and also with regard to the form of the assumed galactic spectrum at low energies. The relationship between the proton and helium spectra derived here and the heavier nuclei spectral differences recently reported in the literature is also examined.If rigidity spectra are adopted for protons and helium nuclei, then the source abundance ratio of these two components is determined to be 7:1. Some cosmological implications of this ratio are discussed.     

Astronomy with a mid-infrared echelle spectrograph

Irshell, a mid-infrared echelle spectrograph developed through a collaboration between the University of Texas, the University of California Space Sciences Laboratory, and Hughes Aircraft, has been in regular use for astronomical observations for about five years. It is optimized for high spectral resolution (R10,000) observations of narrow spectral regions (/1/300) and compact sources (a few arcsec), and is sensitive in the 5–25 m region. A wide variety of astronomical objects have been studied. Observing techniques have been developed to achieve maximum sensitivity in those observations for which Irshell is best suited and to allow observations of wide spectral regions and extended objects. We discuss the observing techniques and show some of the data obtained.     

SERTS-97 Measurements Of Relative Wavelength Shifts In Coronal Emission Lines Across A Solar Active Region

We used slit spectra from the 18 November 1997 flight of Goddard Space Flight Center's Solar EUV Rocket Telescope and Spectrograph (SERTS-97) to measure relative wavelength shifts of coronal emission lines as a function of position across NOAA active region 8108. The shifts are measured relative to reference wavelengths derived from spectra of the region's nearby quiet surroundings (not necessarily at rest) because laboratory rest wavelengths for the coronal EUV lines have not been measured to sufficient accuracy for this work. An additional benefit to this approach is that any systematic uncertainties in the wavelength measurements are eliminated from the relative shifts by subtraction. We find statistically significant wavelength shifts between the spatially resolved active region slit spectra and the reference spectrum. For He ii 303.78 Å the maximum measured relative red shift corresponds to a Doppler velocity +13 km s^–1, and the maximum relative blue shift corresponds to a Doppler velocity –3 km s^–1. For Si x 347.40 Å, Si xi 303.32 Å, Fe xiv 334.17 Å, and Fe xvi 335.40 Å the corresponding maximum relative Doppler velocities are +19 and –14, +23 and –7, +10 and –10, and +13 and –5 km s^–1, respectively. The active region appears to be divided into two different flow areas; hot coronal lines are predominantly red-shifted in the northern half and either blue-shifted or nearly un-shifted in the southern half. This may be evidence that material flows up from the southern part of the region, and down into the northern part. Qualitatively similar relative wavelength shifts and flow patterns are obtained with SOHO/CDS spectra.     

Immediate reports of GRBs in progress from HETE

The High Energy Transient Experiment (HETE) will be able to perform multiwavelength observations of-ray and X-ray bursts. HETE will potentially be able to localize-ray bursts to a precision of 20 arc-minutes if significant X-ray flux is detected from the burst; a precision of 20 arc-seconds is possible if there is also significant UV radiation from the burst. HETE will broadcast information about bursts detected within seconds of their detection. This VHF-band broadcast will be received at a number of secondary ground stations (SGS) dedicated to HETE, and forwarded to a central distribution site at MIT, from which it is sent to interested observers via Internet.     

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.     

Wide field X-ray monitor on board the High Energy Transient Experiment (HETE)

The High-Energy Transient Experiment (HETE) is designed for the multiwavelengths study of Gamma-Ray Bursts (GRBs) in UV, X-ray and gamma-ray range with three scientific instruments. The X-ray instrument, Wide-field X-ray Monitor (WXM), consists of four units of one-dimensional position sensitive gas proportional counters and two perpendicularly oriented one-dimensional coded apertures. The WXM has a wide FOV of 1.5 steradian together with the capability to locate GRBs with 10 arcmin accuracy, and covers photon energies of 2 to 25 keV with an energy resolution of typically 18 % at 6 keV, measuring wide band spectra together with the gamma-ray spectrometer (FREGATE). The coded X-ray image will be deconvolved on board and the GRB location will be provided to the UV camera within 1 sec . GRB locations will also be broadcast in real time to ground-based observers for follow-up observations.     

Rapid changes in the fine structure of a coronal ‘bright point’ and a small coronal ‘active region’

A coronal bright point is resolved into a pattern of emission which, at any given time, consists of 2 or 3 miniature loops (each 2500 km in diameter and 12 000 km long). During the half-day lifetime of the bright point individual loops evolved on a time scale 6 min. A small ctive region seemed to evolve in this way, but the occasional blurring together of several loops made it difficult to follow individual changes.     

Oxygen abundances in old disc and halo stars of the Galaxy

Intermediate resolution (/ 25 000) CCD spectra of the oxygen triplet at 7770 Å have been analyzed to determine oxygen abundances in a sample of metal-deficient stars with metallicities covering the range –2.5[Fe/H]–0.2. Important oxygen overabundances ([O/Fe]1) are found in the more metal deficient stars of the sample. We briefly discuss the information that these observations provide about the early nucleosynthesis history and chemical evolution of the Galaxy.     

The solar O i λ 7773 triplet

The reduction of observations of the O i 7773 triplet obtained at high spatial resolution (0.5) at two disk positions is described. Two sets of triplet profile data are presented at each disk position. One set represents data taken from 0.5 regions centered on the brightest granules, while the other set represents data taken from 0.5 regions centered on the cooler infalling intergranular material.     

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.     

Cosmic gamma-ray burst from intergalactic relativistic dust grains

Charged dust grains of radiia3×10^–63×10^–5 cm may acquire relativistic energy (>10¹⁸ eV) in the intergalactic medium. In order to attain relativistic energy, dust grains have to move in and out (scattering) of the magnetic field of the medium. A relativistic grain of radiusa10^–5 cm with Lorentz factor 10³ approaching the Earth will break up either due to electrostatic charge or due to sputtering about 150100 km, and may scatter solar photons via a fluorescence process. Dust grains may also melt into droplets in the solar vicinity and may contribute towards observed gamma-ray bursts.     

Absolute wavelengths of Fraunhofer lines: Convective motions in the solar photosphere and the gravitational red shift

Absolute wavelengths for Fraunhofer lines are compared with laboratory measurements for several atomic and molecular spectra. The wavelength differences are shown to be consistent with the proposal that the deeper layers of the photosphere are in convective motion: _e -3 km/sec for log ₀> -1.0. Convective motions in the outer layers (log₀< - 1.0) are shown to be very small. Wavelength shifts of Fraunhofer lines formed in these outer layers are in good quantitative agreement with the predictions of the General Theory of Relativity.     

Generation of γ-bursts by old magnetic neutron stars

A model of -bursts is considered that treats the flares of neutron stars as a result of convectiveoscillation instability associated with the stars having strong internal magnetic fields ( 10¹³ to 10¹⁴ G). In the context of this model only sufficiently old (10⁴ to 10⁷ yr), drastically cooled-down neutron stars may be sources of -bursts. The paper shows that major characteristics of a -burster in the Supernova N 49 remnant (energy release during burst up to 10⁴⁴ erg, age 10⁴ yr, burst-to-burst interval (I to 3)×10⁶s; rotation period P=8 s) may be explained under the assumption that the mass of the neutron star is about 0.14M _· while its mean magnetic field strength is 1.5×10¹⁴ G abd 10¹³ G within the star and on its surface, respectively. The observational tests of the model discussed conclude the paper.     

A reexamination of the Gum nebula

A detailed analysis of interstellar measurements in the direction of the Gum nebula is carried out. The ionized region is shown to have an angular radius of 18° and appears to be bounded by a shell of neutral gas. The mean electron temperature deduced from radio-frequency absorption measurements is found to be 8500K. These parameters suggest that the nebula is the normal and possibly evolved Hii region of Pup and ² Vel, rather than the fossil Strömgren sphere of the Vela supernova as suggested by Brandtet al. (1971).     

CASPIR: A cryogenic array spectrometer imager for the MSSSO 2.3 m telescope

CASPIR is a near-infrared spectrometer/imager being built for the Mount Stromlo and Siding Spring Observatories' 2.3 m telescope. The instrument is based on a SBRC 256×256 InSb detector array and uses AR-coated Sapphire, MgO, CaF₂, and BaF₂ optics to produce two imaging focal plane scales with 0.5/pixel and 0.25/pixel. Spectral resolving powers of 500 will be achieved through a 1×128 slit with three grisms designed for the J, H, and K bands. IJ, JH, and HK cross-dispersed échelle grisms will achieve resolving powers of 1100 through a 1×15 slit. Coronograph and imaging polarimetry modes will also be available. The various observing configurations are selected via five remotely controlled wheels. The instrument design and system architecture are discussed, and preliminary detector performance figures reported.