Cosmic-ray modulation ground-based observations

Summary This rapporteur paper discusses some achievements in the understanding of cosmic-ray solar modulation with ground-based observations presented at the XXIV International Cosmic Ray Conference. Rapporteur talk given at the XXIV International Cosmic-Ray Conference, Rome, August 28–September 8, 1995.     

High-energy interactions

Summary This paper, based on the rapporteur talk given at the XXIV International Cosmic-Ray Conference (Roma, 28 August–8 September 1995), concerns the sessions HE1, HE2, HE6. Multihadron production in cosmic rays, models, emulsion chamber measurements, simulation of electromagnetic and hadronic cascades, new particles and processes are summarized in the frame of the special phenomenology adapted to the collisions of ultrahigh-energy particles in the atmosphere. Rapporteur talk given at the XXIV International Cosmic-Ray Conference, Rome, August 28–September 8, 1995.     

Paleoastrophysics and cosmic rays

Summary A discussion is given of the status and potential of studying the cosmic-ray flux level over long time scales by high-precision measurement of cosmogenic isotopes content in natural archives of cosmic radiation. Invited talk given at the XXIV International Cosmic-Ray Conference, Rome, August 28–September 8, 1995.     

3D heliospheric simulations of cosmic rays in the light of Ulysses

Summary Recent Ulysses observations in the polar regions of the heliosphere have provided fundamental new insights into the modes of cosmic-ray transport in the heliosphere. Ulysses discovered variations in the magnetic field which are large enough to produce significant cosmic-ray effects, and which are consistent with a previous prediction. In addition to impeding the inward, radial diffusive and drift access of cosmic rays over the poles as discussed previously, the magnetic fluctuations imply a significantly larger latitudinal diffusion. These effects directly lead to both a much reduced latitudinal gradient and significant 27-day time variations near the pole. We conclude that the general picture of cosmic-ray transport and modulation developed over the past decade, with reasonable parameters, can account for most of the observed global, large-scale phenomena. Paper presented at the Special Session on the Ulysses mission of the XXIV International Cosmic-Ray Conference, Rome, August 28–September 8, 1995.     

Cosmic-ray propagation in the Galaxy

Summary More than 95 contributed papers on cosmic-ray transport and acceleration in the Galaxy were presented at the XXIV International Cosmic-Ray Conference. The present summary covers part of the rapporteur talk and reflects a personal view of the subject. Rapporteur talk given at the XXIV International Cosmic-Ray Conference, Rome, August 28–September 8, 1995.     

The enrichment of physics and astrophysics: The legacy of Victor Hess

Summary The Third Victor F. Hess Memorial Lecture traces the evolution of the cosmic-ray discipline from Hess' discovery in his balloon flights of 1911. Serendipitously, this led to the genesis of two major fields of research, high-energy elementary-particle physics and cosmic-ray astrophysics. The subsequent development of the latter field is traced from the early decades when its promise was not widely appreciated. Epochal discoveries in the 1930's and 1940's stimulated widespread interest among physicists. Identification of the positron, the ?soft component?, muons, pions, and the elaboration of the electromagnetic theory of shower production were among the major advances. The nuclear character of the main primary component was demonstrated in the forties. Symbiosis with radioastronomy, notably the understanding of the synchrotron radiation emitted from the Crab Nebula, revealed the role of supernova explosions in providing the energy for the galactic cosmic radiation. Fermi's use of magnetohydrodynamics in his acceleration mechanisms, and their subsequest realization in shock-wave theory are sketched. Detailed investigations of composition—especially measurements of the Li−Be−B and of the³He components—yielded knowledge of the propagation and transformations of the relativistic nuclei in passing through the interstellar medium. This, in turn, made possible the evaluation of path length distributions, predictions of the arriving isotopic composition, the source composition, and cosmic-ray age. Finally, some tantalizing problems that remain are mentioned, notably those of the highest-energy and the lowest-energy cosmic rays. Invited talk given at the XXIV International Cosmic-Ray Conference, Rome, August 28–September 8, 1995.     

High-energy cosmic-ray interactions

Summary The problems under review include unusual results observed in cosmic-ray investigations which were not explained and are now up-to-date. Paper presented at the Special Session on very high-energy cosmic-ray interactions (superfamilies) of the XXIV International Cosmic-Ray Conference, Rome, August 28–September 8, 1995.     

Solar cosmic rays

Summary This report is a brief overview of the energetic-particle phenomena related to solar activity discussed at the XXIV International Cosmic-Ray Conference. In the rapporteur's opinion, the most significant results to be highlighted are: 1) the new higher-energy measurements of the solar energetic ion charge state which seem to be consistent with the older measurements at ∼1 MeV/nucleon, and 2) the many reports of extended gamma-ray production during solar flares with multiple episodes of emission implying multiple episodes of particle acceleration. Rapporteur talk given at the XXIV International Cosmic-Ray Conference, Rome, August 28–September 8, 1995.     

Observations of energetic particles with EPAC on Ulysses in polar latitudes of the heliosphere

Summary Measurements with the EPAC energetic-charged-particle instrument aboard Ulysses show between −15° and −65° ions and, to some extent, also electrons apparently accelerated by shocks associated with a cororating interaction region (CIR) operating at low latitudes. Particles could have reached Ulysses along magnetic-field lines which connect to the shocks in the more distant heliosphere. Such connections evidently do not exist above −65°. Between the recurrent streams we find the underlying composition to be similar to that of the anomalous component of cosmic rays (ACR). One channel (ELH), sensitive also to high-energy protons (E>210 MeV), shows that, superimposed to the large-scale heliospheric modulation of galactic ions, a 26-day variation of the flux is observed. Such modulation is also observed for the ACR, in phase with the galactic particle modulation, but anticorrelated to the CIR-related low-energy particles. An estimate of the latitudinal and radial gradients of the galactic cosmic rays at 1 GV gives +0.4%/degree and −11%/AU, respectively. Paper presented at the Special Session on the Ulysses mission of the XXIV International Cosmic-Ray Conference, Rome, August 28–September 8, 1995.     

Ulysses cosmic-ray investigations extending from the south to the north polar regions of the Sun and heliosphere

Summary The recent rapid transit of Ulysses from the solar south polar to the north polar region has confirmed the earlier findings by the COsmic-ray and Solar-Particle Investigations (COSPIN) international consortium and has yielded additional discoveries that are important for understanding heliospheric modulation. High-resolution isotopic measurements of Fe and Ni on Ulysses show that the source composition of these cosmic-ray nuclei is not neutron rich for these elements and is close to solar-system composition. Paper presented at the Special Session on the Ulysses mission of the XXIV International Cosmic-Ray Conference, Rome, August 28–September 8, 1995. See also the Rapporteur paper by J. W. Bieber (Nuovo Cimento C,19 (1996) 777) for a summary of the papers on this subject.     

Azimuthal peculiarities of gamma-ray-hadron families and the new physics at ?s\sqrt s ? TeVTeV

Summary Results of the analysis of possible causes of the alignment of energetically distinguished cores of γ-hadron families are presented. It is shown that the well-known physical factors cannot produce the observed effects. A phenomenological model based on new Pomeron physics theories and capable of explanation of this phenomenon is proposed. Paper presented at the Special Session on very high-energy cosmic-ray interactions (superfamilies) of the XXIV International Cosmic-Ray Conference, Rome, August 28–September 8, 1995.     

Ground-based gamma-ray astronomy

Summary This report covers developments in the field of gamma-ray astronomy, essentially in the energy range 300 GeV to 300 TeV, reported at the XXIV International Cosmic-Ray Conference in Rome in 1995. Highlights which receive the main attention are the failure of several experiments to detect TeV photons from several supernova remnants at the level predicted on current models of shock acceleration of cosmic-ray protons, and the detection of a rapidly variable flaring output of TeV photons from two BL Lac objects (Markarian 421 and Markarian 501). Although techniques are now maturing to the extent that different measurements of the flux and spectrum from the Crab Nebula are now converging, unresolved differences remain over the existence of TeV pulses from certain pulsars. However, one well-supported instance of very intense pulsation for an hour from AE Aquarii was presented. The Vela Pulsar was reported as a steady source. Rapporteur talk given at the XXIV International Cosmic-Ray Conference, Rome, August 28–September 8, 1995.     

Gamma-ray astronomy by the air shower technique: Performance and perspectives

Summary The techniques for γ-ray astronomy at energies ≥10 TeV using air shower detectors are discussed. The results, based on a number of large arrays, are negative, with no point sources being identified. While the contributions to γ-ray astronomy so far have been only upper limits, these arrays in the future will make significant progress in the understanding of cosmic rays in the energy range 10¹³ eV to 10¹⁶ eV. Also, contributions to solar physics are being made by observations of shape and time dependence of the shadow of the Sun as observed in cosmic rays. For the advancement of γ-ray astronomy a greater sensitivity is required in the energy region of 10 TeV. A number of promising techniques to accomplish a greater sensitivity are discussed. They include the enlargement of the Tibet array at 4300 meters altitude, the array of open photomultipliers at La Palma (AIROBICC), which views the shower by the Cherenkov photons produced in the atmosphere, and the instrumentation of a pond at Los Alamos with photomultipliers (Milagro). Invited talk given at the XXIV International Cosmic-Ray Conference, Rome, August 28–September 8, 1995.     

Attenuation mean free path of hadrons in super-families

Summary Results are presented from the collaboration work of groups of Moscow State University and Waseda University with Pamir X-ray film chamber of thick Pb type. Hadrons in 58 families with energy >100 TeV are studied. The attenuation m.f.p. is 233±40 g/cm² in Pb. Paper presented at the Special Session on very high-energy cosmic-ray interactions (super-families) of the XXIV International Cosmic-Ray Conference, Rome, August 28–September 8, 1995.     

Superyoung EAS with N e>107. The ?Hadron? experiment

Summary The combined (EAS+EC) ?Hadron? experiment was made at Tien-Shan Station during 1985–1991. A large statistic of gamma-hadron families, combined with EAS, is now analysed. The result of the leader effect disappearance forN _e>10⁷ was reported earlier and at this Conference too. Here we present new results about the existence of Super Young Showers (SYS) with ageS<0.1, containing gamma-hadron families with visible energy ≥10 TeV. Namely, SYS have anomalous soft-energy spectra of particles at gamma-hadron families. These events may be connected with Young Air Showers (YAS) and Narrow Air Showers (NAS). Paper presented at the Special Session on very high-energy cosmic-ray interactions (superfamilies) of the XXIV International Cosmic-Ray Conference, Rome, August 28–September 8, 1995.     

Cosmic-ray spectrum and composition: Ground observations

Summary This paper summarizes the most interesting results obtained from ground-based experiments investigating cosmic-ray spectrum and composition. The contributed measurements cover a range of primary energy of about 7 decades, from ∼10¹³ eV up to ∼10²⁰ eV, allowing us to gain deeper insight into a large variety of phenomena including: source and acceleration mechanisms, propagation and diffusion in the Galaxy, extragalactic sources and their location. Rapporteur talk given at the XXIV International Cosmic-Ray Conference, Rome, August 28–September 8, 1995.     

Antimatter in the Universe

Summary The evidence for cosmologically significant amounts of antimatter in the Universe is reviewed. There is no compelling evidence, either theoretical or experimental, for a baryon-symmetric Universe. The possibility is not completely ruled out, however. This essay is dedicated to the memory of the late Robert Golden, a pioneer in the search for antimatter in the cosmic radiation. Invited talk given at the XXIV International Cosmic-Ray Conference, Rome, August 28–September 8, 1995.     

Development of the atmospheric Cherenkov imaging technique

Summary Following a brief history of the atmospheric Cherenkov imaging technique and a summary of the current status of the field, we describe some of the potential developments of the method over the next few years. Due to constraints of space, we shall confine the discussion to single stand-alone telescopes—stereo imaging will not be discussed. Paper presented at the Special Session on ground-based gamma-ray astronomy of the XXIV International Cosmic-Ray Conference, Rome, August 28–September 8, 1995.     

Ground-based gamma-ray astronomy: General remarks

Summary The ground-based gamma-ray astronomy has its coming of age currently with 4 sources detected at high significance levels, after experiencing about 30 years history. The energetic gamma rays provide direct means for uncovering higher-energy non-thermal phenomena at various celestial objects. We need more data with improved sensitivities, and multitudes of such efforts are now under way. Paper presented at the Special Session on ground-based gamma-ray astronomy of the XXIV International Cosmic-Ray Conference, Rome, August 28–September 8, 1995.