PAMELA results on the cosmic-ray antiproton flux from 60 MeV to 180 GeV in kinetic energy

The satellite-borne experiment PAMELA has been used to make a new measurement of the cosmic-ray antiproton flux and the antiproton-to-proton flux ratio which extends previously published measurements down to 60 MeV and up to 180 GeV in kinetic energy. During 850 days of data acquisition approximately 1500 antiprotons were observed. The measurements are consistent with purely secondary production of antiprotons in the galaxy. More precise secondary production models are required for a complete interpretation of the results.Comment: 11 pages, 3 figures, 1 table. Accepted for publication in Physical Review Letter

Correlations between earthquakes and anomalous particle bursts from SAMPEX/PET satellite observations.

In the last decades, a possible influence of electromagnetic fields of seismic origin in the ionosphere–magnetosphere transition region has been reported in the literature. In recent years, a few space experiments also revealed anomalous bursts of charged particles precipitating from the lower boundary of the inner radiation belt. They were thought to be caused by low-frequency seismo-electromagnetic emissions. A recent study [Aleksandrin et al., 2003. Annales Geophysicae 21, 597–602] seems to confirm that these particle bursts have a short-term preseismic character. The particle longitudinal drift should enhance the detectability of preseismic particle bursts, thus magnifying their importance in earthquake prediction studies. This paper takes into consideration the method introduced by Aleksandrin et al. (2003) to carry out a deeper investigation on the subject. In this sense, a method for the temporal correlation between continental earthquakes with MX5:0 and anomalous particle bursts collected by the PET- SAMPEX satellite mission is critically investigated and presented here. Several constraints and cuts have been applied to data in order to exclude, from the correlation, charged particles collected inside the SAA region and/or during ionospheric and magnetospheric perturbations caused by non-seismic sources. After the data have been detrended by these effects, a short-term seismic precursor of 4 h is observed in the histogram of the time difference between the time occurrence of earthquakes and that of particle burst events. The best correlation is obtained only when considering high-energy electrons (EX4 MeV) with pitch angles near the loss cone. Such a result confirms previous ones but also points out the importance of an ad hoc method of analysis. Results suggest the importance of coordinated and simultaneous ground-based and space investigations specifically dedicated to the subject. Also, a deeper investigation based on particle data prepared and analyzed as carefully as possible is requested to understand the physical mechanisms underlying the phenomenon under study

Time Dependence of the electron and positron components of the cosmic radiation measured by the PAMELA experiment between July 2006 and December 2015

Cosmic-ray electrons and positrons are a unique probe of the propagation of cosmic rays as well as of the nature and distribution of particle sources in our Galaxy. Recent measurements of these particles are challenging our basic understanding of the mechanisms of production, acceleration, and propagation of cosmic rays. Particularly striking are the differences between the low energy results collected by the space-borne PAMELA and AMS-02 experiments and older measurements pointing to sign-charge dependence of the solar modulation of cosmic-ray spectra. The PAMELA experiment has been measuring the time variation of the positron and electron intensity at Earth from July 2006 to December 2015 covering the period for the minimum of solar cycle 23 (2006-2009) until the middle of the maximum of solar cycle 24, through the polarity reversal of the heliospheric magnetic field which took place between 2013 and 2014. The positron to electron ratio measured in this time period clearly shows a sign-charge dependence of the solar modulation introduced by particle drifts. These results provide the first clear and continuous observation of how drift effects on solar modulation have unfolded with time from solar minimum to solar maximum and their dependence on the particle rigidity and the cyclic polarity of the solar magnetic field

Cosmic ray electrons and positrons over decade with the PAMELA experiment

The PAMELA experiment has measured cosmic ray particles and antiparticles fluxes at Earth orbit from June 2006 till January 2016 onboard the Resurs-DK1 satellite. Measurements were carried out during the solar minimum of 23 solar cycle with negative polarity A < 0 of heliospheric magnetic field till the beginning of 24 cycle with positive polarity A > 0. In this paper, the results of observations of electron and positron fluxes are presented in wide energy range from several hundreds MeVs till several TeVs These measurements provide important information to study cosmic ray sources and propagation in Galaxy and heliosphere

Trapped antiprotons in the Earth inner radiation belt in PAMELA experiment

The existence of trapped antiprotons in the Earth's inner radiation belt has been theoretically predicted, but not observed. We present a procedure for antiproton selection and the observation results from the PAMELA space experiment measurements. The PAMELA magnetic spectrometer ensures reliable identification of particles and charge signs, value determination, and energy measurement, thus enabling us to experimentally establish the existence of antiprotons trapped in the Earth's inner radiation belt

Unexpected Cyclic Behavior in Cosmic-Ray Protons Observed by PAMELA at 1 au

Protons detected by the PAMELA experiment in the period 2006-2014 have been analyzed in the energy range between 0.40-50 GV to explore possible periodicities besides the well known solar undecennial modulation. An unexpected clear and regular feature has been found at rigidities below 15 GV, with a quasi-periodicity of $\sim$450 days. A possible Jovian origin of this periodicity has been investigated in different ways. The results seem to favor a small but not negligible contribution to cosmic rays from the Jovian magnetosphere, even if other explanations cannot be excluded.Comment: article 4 figures, 1 tabl

Solar modulation of galactic cosmic rays during 2006-2015 based on PAMELA and ARINA data

Solar modulation of galactic protons with energies from 50 MeV up to dozens of GeV during July '06 - January '16 studied based on a data of the magnetic spectrometer PAMELA and scintillation spectrometer ARINA. This period is interesting because it covers the end of 23rd and current 24th cycles of solar activity, including the abnormally long transient period and change of the polarity of solar magnetic field

Evidence of Energy and Charge Sign Dependence of the Recovery Time for the 2006 December Forbush Event Measured by the PAMELA Experiment

New results on the short-term galactic cosmic ray (GCR) intensity variation (Forbush decrease) in December 2006 measured by the PAMELA instrument are presented. Forbush decreases are sudden suppressions of the GCR intensities which are associated with the passage of interplanetary transients such as shocks and interplanetary coronal mass ejections (ICMEs). Most of the past measurements of this phenomenon were carried out with ground-based detectors such as neutron monitors or muon telescopes. These techniques allow only the indirect detection of the overall GCR intensity over an integrated energy range. For the first time, thanks to the unique features of the PAMELA magnetic spectrometer, the Forbush decrease commencing on 2006 December 14, following a CME at the Sun on 2006 December 13 was studied in a wide rigidity range (0.4 - 20 GV) and for different species of GCRs detected directly in space. The daily averaged GCR proton intensity was used to investigate the rigidity dependence of the amplitude and the recovery time of the Forbush decrease. Additionally, for the first time, the temporal variations in the helium and electron intensities during a Forbush decrease were studied. Interestingly, the temporal evolutions of the helium and proton intensities during the Forbush decrease were found in good agreement, while the low rigidity electrons (< 2 GV) displayed a faster recovery. This difference in the electron recovery is interpreted as a charge-sign dependence introduced by drift motions experienced by the GCRs during their propagation through the heliosphere

Secondary positrons and electrons in near-Earth space in the PAMELA experiment

Fluxes of electrons and positrons with energies above ~100 MeV in the near-Earth space are measured with the PAMELA magnetic spectrometer aboard the Resurs DK-1 satellite launched on June 15, 2006, into a quasipolar orbit with an altitude of 350–600 km and an inclination of 70°. Calculating the trajectories of detected electrons and positrons in the magnetosphere of the Earth allows us to determine their origin and isolate particles produced during interaction between cosmic rays and the residual atmosphere. Spatial distributions of albedo, quasitrapped, and trapped (in the radiation belt) positrons and electrons are presented. The ratio of positron and electron fluxes suggests that the fluxes of trapped particles of the radiation belt and quasitrapped secondary particles have different mechanisms of formation