| 1. |
- Munini, R., et al.
(författare)
-
Evidence of Energy and Charge Sign Dependence of the Recovery Time for the 2006 December Forbush Event Measured by the PAMELA Experiment
- 2018
-
Ingår i: Astrophysical Journal. - : Institute of Physics Publishing (IOPP). - 0004-637X .- 1538-4357. ; 853:1
-
Tidskriftsartikel (refereegranskat)abstract
- New results on the short-term galactic cosmic-ray (GCR) intensity variation (Forbish decrease) in 2006 December 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 groundbased 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 and 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 to be 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.
|
|
| 2. |
- Adriani, O., et al.
(författare)
-
MEASUREMENTS OF COSMIC-RAY HYDROGEN AND HELIUM ISOTOPES WITH THE PAMELA EXPERIMENT
- 2016
-
Ingår i: Astrophysical Journal. - 0004-637X .- 1538-4357. ; 818:1
-
Tidskriftsartikel (refereegranskat)abstract
- The cosmic-ray hydrogen and helium (H-1, H-2, He-3, He-4) isotopic composition has been measured with the satellite-borne experiment PAMELA, which was launched into low-Earth orbit on board the Resurs-DK1 satellite on 2006 June 15. The rare isotopes H-2 and He-3 in cosmic rays are believed to originate mainly from the interaction of high-energy protons and helium with the galactic interstellar medium. The isotopic composition was measured between 100 and 1100 MeV/n for hydrogen and between 100 and 1400 MeV/n for helium isotopes using two different detector systems over the 23rd solar minimum from 2006 July to 2007 December.
|
|
| 3. |
- Adriani, O., et al.
(författare)
-
Pamela's measurements of magnetospheric effects on high-energy solar particles
- 2015
-
Ingår i: Astrophysical Journal Letters. - 2041-8205 .- 2041-8213. ; 801:1
-
Tidskriftsartikel (refereegranskat)abstract
- The nature of particle acceleration at the Sun, whether through flare reconnection processes or through shocks driven by coronal mass ejections, is still under scrutiny despite decades of research. The measured properties of solar energetic particles (SEPs) have long been modeled in different particle-acceleration scenarios. The challenge has been to disentangle the effects of transport from those of acceleration. The Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA) instrument enables unique observations of SEPs including the composition and angular distribution of the particles about the magnetic field, i.e., pitch angle distribution, over a broad energy range (>80 MeV)-bridging a critical gap between space-based and ground-based measurements. We present high-energy SEP data from PAMELA acquired during the 2012 May 17 SEP event. These data exhibit differential anisotropies and thus transport features over the instrument rigidity range. SEP protons exhibit two distinct pitch angle distributions: a low-energy population that extends to 90 degrees and a population that is beamed at high energies (>1 GeV), consistent with neutron monitor measurements. To explain a low-energy SEP population that exhibits significant scattering or redistribution accompanied by a high-energy population that reaches the Earth relatively unaffected by dispersive transport effects, we postulate that the scattering or redistribution takes place locally. We believe that these are the first comprehensive measurements of the effects of solar energetic particle transport in the Earth's magnetosheath.
|
|
| 4. |
- Adriani, O., et al.
(författare)
-
Reentrant albedo proton fluxes measured by the PAMELA experiment
- 2015
-
Ingår i: Journal of Geophysical Research - Space Physics. - 2169-9380 .- 2169-9402. ; 120:5, s. 3728-3738
-
Tidskriftsartikel (refereegranskat)abstract
- We present a precise measurement of downward going albedo proton fluxes for kinetic energy above similar to 70 MeV performed by the Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA) experiment at an altitude between 350 and 610 km. On the basis of a trajectory tracing simulation, the analyzed protons were classified into quasi-trapped, concentrating in the magnetic equatorial region, and untrapped spreading over all latitudes, including both short-lived (precipitating) and long-lived (pseudotrapped) components. In addition, features of the penumbra region around the geomagnetic cutoff were investigated in detail. PAMELA results significantly improve the characterization of the high-energy albedo proton populations at low-Earth orbits.
|
|
| 5. |
|
|
| 6. |
- Adriani, O., et al.
(författare)
-
Ten years of PAMELA in space
- 2017
-
Ingår i: La Rivista del nuovo cimento della Società italiana di fisica. - : Società Italiana di Fisica. - 0393-697X .- 1826-9850. ; 40:10, s. 473-522
-
Tidskriftsartikel (refereegranskat)abstract
- The PAMELA cosmic-ray detector was launched on June 15th 2006 on board the Russian Resurs-DK1 satellite, and during ten years of nearly continuous data-taking it has observed new interesting features in cosmic rays (CRs). In a decade of operation it has provided plenty of scientific data, covering different issues related to cosmic-ray physics. Its discoveries might change our basic vision of the mechanisms of production, acceleration and propagation of cosmic rays in the Galaxy. The antimatter measurements, focus of the experiment, have set strong constraints to the nature of Dark Matter. Search for signatures of more exotic processes (such as the ones involving Strange Quark Matter) was also pursued. Furthermore, the long-term operation of the instrument had allowed a constant monitoring of the solar activity during its maximum and a detailed and prolonged study of the solar modulation, improving the comprehension of the heliosphere mechanisms. PAMELA had also measured the radiation environment around the Earth, and it detected for the first time the presence of an antiproton radiation belt surrounding our planet. The operation of Resurs-DK1 was terminated in 2016. In this article we will review the main features of the PAMELA instrument and its constructing phases. The main part of the article will be dedicated to the summary of the most relevant PAMELA results over a decade of observation.
|
|
| 7. |
- Adriani, O., et al.
(författare)
-
Time Dependence of the Electron and Positron Components of the Cosmic Radiation Measured by the PAMELA Experiment between July 2006 and December 2015
- 2016
-
Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 116:24
-
Tidskriftsartikel (refereegranskat)abstract
- 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.
|
|
| 8. |
- Adriani, O., et al.
(författare)
-
Unexpected Cyclic Behavior in Cosmic-Ray Protons Observed by PAMELA at 1 au
- 2018
-
Ingår i: Astrophysical Journal Letters. - : IOP PUBLISHING LTD. - 2041-8205 .- 2041-8213. ; 852:2
-
Tidskriftsartikel (refereegranskat)abstract
- Protons detected by the PAMELA experiment in the period 2006-2014 have been analyzed in the energy range between 0.40 and 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 similar to 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.
|
|
| 9. |
- Boezio, M., et al.
(författare)
-
Nine years of cosmic rays investigation by the PAMELA experiment
- 2015
-
Ingår i: Proceedings of Science. - : Proceedings of Science (PoS).
-
Konferensbidrag (refereegranskat)abstract
- The PAMELA cosmic ray detector was launched on June 15th of 2006 on board the Russian Resurs-DK1 satellite and during nine years of continuous data-taking it has ob- served very interesting features in cosmic rays, namely in the fluxes of protons, helium and electrons. Its discoveries might change our basic vision of the mechanisms of pro- duction, acceleration and propagation of cosmic rays in the Galaxy. Moreover, PAMELA measurements of cosmic antiproton and positron fluxes and positron-to-all-electron ratio have been setting strong constraints to the nature of Dark Matter. Measurements of boron, carbon, lithium and beryllium (together with the isotopic fraction) will also shed new light on the elemental composition of the cosmic radiation. Search for signatures of more exotic processes (such as the ones involving Strange Quark Matter) is also pursued. Furthermore, the instrument is still functional allowing a constant monitoring of the solar activity during its maximum and a detailed and prolonged study of the solar modulation, improving the comprehension of the heliosphere mechanisms. PAMELA is also measur- ing the radiation environment around the Earth, and it detected for the first time the presence of an antiproton radiation belt surrounding our planet. In this highlight paper PAMELA main results will be reviewed.
|
|
| 10. |
- Boezio, M., et al.
(författare)
-
The PAMELA experiment : A cosmic ray experiment deep inside the heliosphere
- 2017
-
Ingår i: Proceedings of Science. - : Sissa Medialab Srl.
-
Konferensbidrag (refereegranskat)abstract
- It was the 15th of June of 2006 when the PAMELA satellite-borne experiment was launched from the Baikonur cosmodrome in Kazakstan. Then, for nearly ten years, PAMELA has been making high-precision measurements of the charged component of the cosmic radiation opening a new era of precision studies in cosmic rays and challenging our basic vision of the mechanisms of production, acceleration and propagation of cosmic rays in the galaxy and in the heliosphere. The study of the time dependence of the various components of the cosmic radiation from the unusual 23rd solar minimum through the maximum of solar cycle 24 clearly shows solar modulation effects as well as charge sign dependence. PAMELA measurement of the energy spectra during solar energetic particle events fills the existing energy gap between the highest energy particles measured in space and the ground-based domain. Finally, by sampling the particle radiation in different regions of the magnetosphere, PAMELA data provide a detailed study of the Earth s magnetosphere. In this highlight paper, PAMELA main results as well as recent progress about solar and heliospheric physics with PAMELA will be presented.
|
|
