V. G. Stolpovskii

Coronal and interplanetary transport of solar energetic protons and electrons

We present a new method to separate interplanetary and coronal propagation, starting from intensity variations observed by spaceprobes at different heliolongitudes. In general, a decrease in absolute intensities is observed simultaneously with an increase in temporal delays. The coupling of these two effects can be described by Reids model of coronal diffusion and can in principle be used to determine the two coronal time constants, diffusion time tc and escape time A. In addition, a least-squares fit method is used to determine the parameters of interplanetary transport, assuming a radial dependence as λ(r) = λ0(r/1 AU)b. The method is applied to the two solar events of 27 December, 1977 and 1 January, 1978 which were observed by the spaceprobes Helios 1, Helios 2, and Prognoz 6. Energetic particle data are analysed for 13–27 MeV protons and ∼-0.5 MeV electrons. For the regions in space encountered during these events the mean free path of electrons is smaller than that of protons. Straight interpolation between the two rigidities leads to a rather flat rigidity dependence λ(P) ∼ Pn with n = 0.17–0.25. This contradicts the prediction of a constant mean free path or of the transition to scatter-free propagation below about 100 MV rigidity. In three of the four cases the mean free path of 13–27 MeV protons is of the order 0.17 AU, the mean free path of electrons of the order 0.06 AU. For protons we find b ∼- 0.7 for the exponent of the radial variation.The concept of two different coronal propagation regimes is confirmed. It is remarkable that in both regimes electrons are transported more efficiently than protons. This holds for the temporal delay as well as for the amplitude decrease. This is in contrast with the long existing concept of ‘rigidity independent transport’ and puts severe limits to any model of coronal transport. For the December event all three spaceprobes are in the fast propagation regime up to an angular distance of 62°. For protons we find a finite delay even in the fast propagation region, corresponding to a coronal delay rate of about 0.8 hr rad-1 up to 60° angular distance. In contrast, relativistic electrons may reach this distance within a few minutes.The fast transport of electrons and the different behaviour of electrons and protons is in contradiction to the expanding bottle concept. An explanation of coronal transport by shock acceleration directly on open field lines could in principle work in case of protons in the fast propagation region, but would fail in case of the electrons. The fast and efficient transport of electrons is most likely due to a region of field lines extending over a wide range of longitudes directly from the active region into interplanetary space. The much slower transport of both particle types at large azimuthal distances can neither be explained by direct access to open field lines not by the direct shock acceleration concept. A possible explanation is the loop reconnection model in a modified version, allowing for a faster lateral transport of electrons.

Invariant spectral characteristics of the decay phases of energetic electron intensities in solar energetic particle events

Abstract Using simultaneous observations from two Helios s/c, we examined the intensity-time profiles of E > 0.3 MeV electrons during the decay phases of 20 gradual solar energetic particle (SEP) events. As previously found for the SEP event ions, the electron spectra and decay times were nearly invariant over large spatial regions in most events.

CME-driven shocks as a possible source of the electron component in SEP-events

Abstract Contrary to the case of protons and ions, our understanding of the role of coronal mass ejections (CME) and shocks initiated by CMEs in the generation of electrons in solar energetic particle (SEP) events is far from complete. We have considered 65 SEP-events for which it was possible to study relations between the flux profile parameters of E > 0.3 MeV electron enhancements and the velocity of CMEs, as well as characteristics of associated flares. We found that the time to electron peak flux correlates strongly with CME velocity (correlation coefficient is ∼0.7–0.9) both after impulsive and long duration (LDE) flares. The best correlation was obtained in the case of electron enhancements related to flares that were accompanied by hard X-ray bursts with spectrum containing photons with enery

Invariance of Charged Particle Time Profiles at Late Stages of SCR Events from the Data of Multisatellite Observations

Based on the data obtained in simultaneous measurements on the Helios-1 and Helios-2 spacecraft, the properties of the spatial and temporal invariance of spectra of protons with energies more than 4 MeV and electrons with energies more than 0.3 MeV are studied during the phase of intensity decay in events initiated by the following associations: a flare—coronal mass ejection—coronal and interplanetary shock waves. Emphasis is placed on research into the fluxes of electrons, whose possibility to be accelerated by shock waves is problematic. It is shown that the spectra and decay times of both protons and electrons are approximately invariant relative to the flare coordinates in a wide angular range. Depending on the western or eastern spacecraft position in relation to the front part of a shock wave, one observes a delay or advance of the onset of the invariant mode relative to the shock wave arrival, which increases with the growth of the corresponding angular distance.

Study of interrelations between solar energetic particle events, solar flares and coronal mass ejections

Abstract In the last few years the new paradigm of causal relations of active processes in solar atmosphere and interplanetary space is actively propagated. According to it large and long duration solar energetic particle (SEP) events are produced by coronal mass ejections (CMEs), not by solar flares. Nowadays this seems evident for 10 5 – 10 7 eV protons but energetic electrons are still considered to be accelerated exclusively in impulsive phase of solar flares. We discuss the results of the analysis of interrelations between electron component of SEP-events, flares and CMEs on the basis of SEP-event observations onboard various s/c at radial distances of 0.3–1.5 AU during the period 1979–1989. Statistics includes about 68 events related to CUE-flare associations. Dependences of SEP-event time-scales and spectra of 0.03–1.5 MeV electrons on CME speeds and angular widths were considered. Energy spectra of electrons become harder with CUE speed increasing and the spectral exponent γ ∝V −0.5 . More than 20 events were observed simultaneously at various points of the inner heliosphere and the results of multispacecraft observations permit us to consider influence of CME -driven shocks on electron fluxes at various azimutal angles relative to shock nose.

Multi-spacecraft observations of solar energetic and energetic storm particle events during November/December 1982

Abstract Multi-spacecraft observations by Helios, IMP, and Venera show that interplanetary shocks can extend up to more than 90° east of the flare normal and are capable of accelerating particles, in particular protons up to energies of some tens of MeV. At the flanks the shock speed and the acceleration efficiency decrease; this decrease is more pronounced in high than in low energy protons. Shock spikes can be observed at energies up to 50 MeV and shock acceleration seems to be very effective inside 0.5 AU.

Hard X-ray and gamma-ray spectrometer of high resolution and sensitivity on board the international space station (ISS)

Abstract The project of a spectrometer of hard X ( X h -rays and gamma-rays (approximate energy range 0.05 – 50 MeV) was proposed to a competition of scientific instruments to be accommodated onboard the international space station ( ISS ). The objectives of this experiment are as follows: detailed study of astrophysical phenomena including cosmic gamma-ray bursts ( GRB ), lines in Galactic diffuse background, e + e − annihilation line from the Galactic Centre and high resolution observation of solar X h -rays and gamma-radiation in lines and continuum. The spectrometer detector system includes three enriched Ge crystals (each of ∼200 cm 3 volume) cooled to 4 cm 3 volume) with crossed axes. The effective instrument field of view is about π sr. The expected energy resolution at 1 MeV for Ge and NaI are ∼2 keV and ∼50 keV, respectively. The detection of solar flares neutrons is also possible by this instrument owing to the separation of different components of light flashes in CsI . The program of ISS provides a long exposure time for the detectors of the proposed spectrometer. Using results of the “ Grif-1 ” experiment onboard the “ Mir ” station we obtain that it will be possible to accomplish precise X h and gamma-measurements under background conditions onboard ISS .

Long lasting energetic particle injection from a weak flare

Abstract A relatively weak solar cosmic ray event registered at the Earth orbit following the flare of December 17, 1976 is discussed. The main feature of the event is the existence of a prolonged unusually high proton and electron anisotropy; even at the end of the decay phase of the flare the motion of the particles were mainly directed away from the Sun. The durations of proton and electron anisotropies were different. If prolonged particle injection is neglected the value of the anisotropy considerable exceeds all diffusive estimates. Time-intensity and anisotropy profiles of electrons and protons are fitted by a diffusive model including prolonged particle injection at the Sun. The best agreement with the data is obtained if the duration of injection equals about 20 and 7 hours for protons and electrons, respectively.