Muon bursts at the Baksan Underground Scintillation Telescope during energetic solar phenomena

An extended study is performed of short-term bursts of muon intensity recorded at the Baksan Underground Scintillation Telescope (BUST) in 1981-1992. The bursts may be caused by primary protons with energy EpD500 GeV. We summarize the results of data analysis obtained during 18 Ground Level Enhancements (GLE) of solar cosmic rays (SCR). It is proved that at least three of the most significant bursts are associated, with a high probability, with the GLEs of September 29, 1989, June 15, 1991, and October 12, 1981. There are definite evidences that some of 15 other bursts seem to be also associated with energetic solar phenomena—large flares, coronal mass ejections (CME), solar proton events (SPE), etc. Otherwise, it is difficult to explain significant distinctions of their angular and temporal properties from the noise ones. The results make the very specific, strict requirements to possible particle source(s), acceleration and propagation mechanisms. The effect under discussion (“BUST effect”) is suggested to be closely linked with some powerful processes at the Sun, implying possible impact of extended coronal structures, post-eruption energy release, CMEs and coronal (interplanetary) shocks on solar particle acceleration or modulation of galactic cosmic rays (GCR)

Proton energy spectrum and source parameters of the September 29, 1989 event

Ground Level Enhancement (GLE) of solar cosmic rays (SCR) widely observed on September 29, 1989 is studied. The event was remarkable for a number of unusual features. Among them were the double-peak increases observed at some neutron monitor (NM) stations and complicated behaviour of the proton energy spectrum and anisotropy at high rigidities (RF1 GV). Two-component structure of the proton intensity-time profiles in the event has been demonstrated. The first (prompt) component (PC) had a short duration and very hard energy spectrum. The second (delayed) component (DC), being ejected from the Sun A1-2 h later, was dominated by a particle population with the soft spectrum and gradual profiles. By fitting the observed proton spectrum to the calculated one in a computational model with a fast acceleration mechanism at the first, early stage of the event, we estimate parameters of the magnetic field and plasma in the source of the prompt component: B= 91 G; n = 1.23107 cm23 ; L= 109 cm (B, n and L are magnetic field intensity, plasma density at the acceleration site and length of the current sheet, respectively). Such values of B and n are characteristic for the trailing part of coronal transient (behind an eruptive filament) at the coronal heights of several tenths of solar radius, and the value of L is of the order of the filament length

Forbush decreases and solar events seen in the 10 - 20GeV energy range by the Karlsruhe Muon Telescope

Since 1993, a muon telescope located at Forschungszentrum Karlsruhe (Karlsruhe Muon Telescope) has been recording the flux of single muons mostly originating from primary cosmic-ray protons with dominant energies in the 10 - 20 GeV range. The data are used to investigate the influence of solar effects on the flux of cosmic-rays measured at Earth. Non-periodic events like Forbush decreases and ground level enhancements are detected in the registered muon flux. A selection of recent events will be presented and compared to data from the Jungfraujoch neutron monitor. The data of the Karlsruhe Muon Telescope help to extend the knowledge about Forbush decreases and ground level enhancements to energies beyond the neutron monitor regime.Comment: 9 pages, 7 figures, in Press AS

Ground level muons in coincidence with the solar flare of April 15, 2001

The counting rate of single muon tracks from the Project GRAND proportional wire chamber array is examined during the Ground Level Event (GLE) of April 15, 2001. The GLE was seen by neutron monitor stations shortly after the time of the solar X-ray flare. GRAND's single muon data are presented and compared with neutron monitor data from Climax, Newark, and Oulu. The single muon data have mean primary hadron energies higher than those of these neutron monitor stations and so contain information about higher energy hadrons. For the single muon data for Project GRAND, the GLE is detected at a statistical significance of 6.1-sigma.Comment: 9 pages, 6 figure

Relativistic proton production at the sun in the October 28th, 2003 solar event

Abstract In order to infer about the origin of solar relativistic particles (SRP) from the particle event of October 28th, 2003, we proceed to do a confrontation of the experimental energy spectra with the theoretical spectra derived from a transport equation for stochastic acceleration. On basis to a two-source model of particle generation, one of which is associated with an expanding magnetic loop, we solve the transport equation including adiabatic losses simultaneously with the stochastic acceleration process. The confrontation shows that there are two different populations during this event, one of which, the so-called ''delayed component'' may be correctly described by stochastic acceleration, but not the so-called ''prompt component''. We found that the required acceleration efficiencies turn to be very high, so that for this particular event, adiabatic cooling is practically negligible as far as the energy spectrum is concerned. Qualitative inferences point toward a dominated Alfven accelerating turbulence. Our results provide a new support to the existence of two relativistic particle populations in some solar relativistic particle events