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Measurement of Ultra-High Energy Cosmic Rays with CHICOS
Get PDFThe California HIgh school Cosmic ray ObServatory (CHICOS) is a ground-based scintillator array designed to measure the extended air showers of ultra-high energy cosmic rays. The goal of the project is to gain insight into the origin of ultra-high energy cosmic rays by measuring the energy spectrum and the distribution of arrival directions.
The CHICOS array has been in operation since 2003. It consists of 77 pairs of scintillator dectectors deployed at schools in the San Fernando and San Gabriel valleys near Los Angeles, and is designed to observe cosmic ray air showers at energies of 10^18 eV and above. In addition, the Chiquita subarray is designed to observe smaller showers in the energy range of 1016 - 1019 eV.
We present new descriptions of the air shower lateral distribution function and time distribution function, which have been derived from AIRES-generated simulated air showers. The new functions are specific to the CHICOS altitude and allow for a maximum likelihood shower reconstruction method, which is more appropriate to the CHICOS data than the χ2 minimization method. We present several analyses of the accuracy of the reconstruction software in the energy ranges available to the Chiquita and CHICOS arrays.
The energy spectrum between 1017 eV and 1019 eV has been measured by the Chiquita subarray. At the lowest energy range, it is found to agree with previous measurements, while the measured flux falls below previous experiments for energies greater than approximately 1017.5 eV. The CHICOS energy spectrum above 1018.4 eV is found to agree with previous results published by AGASA. However, we do not observe the cutoff in the spectrum at 1020 eV reported more recently by the Auger and HiRes Collaborations.
A correlation analysis between CHICOS data and nearby active galactic nuclei (AGN) was performed. No excess of cosmic rays was observed in the vicinity of nearby AGN. The maximum correlation was observed for cosmic ray events with E > 1020 eV and for AGN with z < 0.009, with Pchance = 21%. This is consistent with random correlations from an isotropic distribution, a result also found by HiRes, but in disagreement with Auger.</p
20. COSMIC RAYS
No full textThe cosmic radiation incident at the top of the terrestrial atmosphere includes all stable charged particles and nuclei with lifetimes of order 106 years or longer. Technically, “primary ” cosmic rays are those particles accelerated at astrophysical sources and “secondaries ” are those particles produced in interaction of the primaries with interstellar gas. Thus electrons, protons and helium, as well as carbon, oxygen, iron, and other nuclei synthesized in stars, are primaries. Nuclei such as lithium, beryllium, and boron (which are not abundant end-products of stellar nucleosynthesis) are secondaries. Antiprotons and positrons are partly, if not entirely, secondaries, but the fraction of these particles that may be primary is a question of current interest. Apart from particles associated with solar flares, the cosmic radiation comes from outside the solar system. The incoming charged particles are “modulated ” by the solar wind, the expanding magnetized plasma generated by the Sun, which decelerates and partially excludes the lower energy galactic cosmic rays from the inner solar system. There is a significant anticorrelation between solar activity (which has an eleven-year cycle) and the intensity of the cosmic rays with energies below about 10 GeV. In addition
The influence of galactic cosmic rays on ion-neutral hydrocarbon chemistry in the upper atmospheres of free-floating exoplanets
No full textThe authors highlight financial support of the European Community under the FP7 by an ERC starting grant.Cosmic rays may be linked to the formation of volatiles necessary for prebiotic chemistry. We explore the effect of cosmic rays in a hydrogen-dominated atmosphere, as a proof-of-concept that ion–neutral chemistry may be important for modelling hydrogen-dominated atmospheres. In order to accomplish this, we utilize Monte Carlo cosmic ray transport models with particle energies of 106 eV<E<1012 eV in order to investigate the cosmic-ray enhancement of free electrons in substellar atmospheres. Ion–neutral chemistry is then applied to a Drift–Phoenix model of a free-floating giant gas planet. Our results suggest that the activation of ion–neutral chemistry in the upper atmosphere significantly enhances formation rates for various species, and we find that C2H2, C2H4, NH3, C6H6 and possibly C10H are enhanced in the upper atmospheres because of cosmic rays. Our results suggest a potential connection between cosmic-ray chemistry and the hazes observed in the upper atmospheres of various extrasolar planets. Chemi-ionization reactions are briefly discussed, as they may enhance the degree of ionization in the cloud layer.Peer reviewe
Observation of New Properties of Secondary Cosmic Rays Lithium, Beryllium, and Boron by the Alpha Magnetic Spectrometer on the International Space Station
Get PDFWe report on the observation of new properties of secondary cosmic rays Li, Be, and B measured in the rigidity (momentum per unit charge) range 1.9 GV to 3.3 TV with a total of nuclei collected by AMS during the first five years of operation aboard the International Space Station. The Li and B fluxes have an identical rigidity dependence above 7 GV and all three fluxes have an identical rigidity dependence above 30 GV with the Li/Be flux ratio of . The three fluxes deviate from a single power law above 200 GV in an identical way. This behavior of secondary cosmic rays has also been observed in the AMS measurement of primary cosmic rays He, C, and O but the rigidity dependences of primary cosmic rays and of secondary cosmic rays are distinctly different. In particular, above 200 GV, the secondary cosmic rays harden more than the primary cosmic rays.Peer Reviewe
Jupiter as a giant cosmic ray detector
No full textAll authors highlight financial support of the European Community under the FP7 by an ERC starting grant.We explore the feasibility of using the atmosphere of Jupiter to detect ultra-high-energy cosmic rays (UHECRs). The large surface area of Jupiter allows us to probe cosmic rays of higher energies than previously accessible. Cosmic ray extensive air showers in Jupiter's atmosphere could in principle be detected by the Large Area Telescope (LAT) on the Fermi observatory. In order to be observed, these air showers would need to be oriented toward the Earth, and would need to occur sufficiently high in the atmosphere that the gamma rays can penetrate. We demonstrate that, under these assumptions, Jupiter provides an effective cosmic ray "detector" area of 3.3 × 107 km2. We predict that Fermi-LAT should be able to detect events of energy >1021 eV with fluence 10-7 erg cm-2 at a rate of about one per month. The observed number of air showers may provide an indirect measure of the flux of cosmic rays ≳ 1020 eV. Extensive air showers also produce a synchrotron signature that may be measurable by Atacama Large Millimeter/submillimeter Array (ALMA). Simultaneous observations of Jupiter with ALMA and Fermi-LAT could be used to provide broad constraints on the energies of the initiating cosmic rays.Peer reviewe
Hydrogen and helium isotopes flux in cosmic rays with the PAMELA experiment
No full textPAMELA is a satellite borne experiment designed to study with great accuracy cosmic rays of galactic, solar, and trapped nature, with particular focus on the antimatter component. The detector consists of a permanent magnet spectrometer core to provide rigidity and charge sign information, a Time-of-Flight system for velocity and charge information, a Silicon-Tungsten calorimeter and a Neutron detector for lepton/hadron identification. The beta and rigidity information allow to identify isotopes for Z = 1 and Z = 2 particles in the energy range 100 MeV/n to 1 GeV/n. In this work we will present the final PAMELA results on the H and He isotope fluxes measured during the 23rd solar minimum from 2006 to 2007. Such fluxes carry relevant information helpful in constraining parameters in galactic cosmic rays propagation models complementary to those obtained from other secondary to primary measurements such as the boron-to-carbon ratio. </p
Gamma rays, cosmic rays and local molecular clouds.
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Electrons in the cosmic radiation
Get PDFThe nature of cosmic ray electrons and their radiation in the Universe has been studied. A convection associated diffusion model is proposed to describe the main characteristics of the large-scale distribution of cosmic ray electrons in the Galaxy: (1) a small Galacto-centric radial gradient; (2) spectral flattening with Galactic latitude; and (3) an extensive halo above the Disk. A new derivation of the interstellar radiation field indicates the existence of an inverse Compton γ -ray halo. This γ -ray halo can contribute up to 60% of the observed diffuse Galactic γ-ray flux at intermediate latitudes and also accounts for the spectral flattening with latitude. This result leads to a new estimate of the extragalactic γ -ray background flux. An energy equipaxtition theory is proposed for the global correlation between radio power and far-infrared luminosity for spiral galaxies, in which the dynamical role of cosmic rays in galactic evolution is implied. The model successfully explains the non-unity slope of the correlation and predicts the escape of cosmic ray electrons from our Galaxy. The interstellar flux of MeV cosmic ray electrons is derived from γ -ray data. The flux is found to be surprisingly high and a new type of source is required. The lower hybrid plasma instability initiated by stellar winds is suggested to be the acceleration mechanism. This high flux of electrons is sufficient to account for the interstellar ionization and heating in HI regions. Features of the local Galactic magnetic field are revealed by analysing pulsar rotation measure data. The large scale regular field is found to be in a bisymmetric configuration and to be stronger in the interarm region (3 µG) than in the arm region (1 µG). The derived small-scale irregular field is shown to have a dominant strength of 6 µG
Changes in cloud cover associated with Forbush decreases of galactic cosmic rays
No full textThe results of a study to quantify the relationship between cloud cover and short-term Forbush decreases (FD) of galactic cosmic ray flux are presented. Using an extensive record of global satellite-derived cloud products from the International Satellite Cloud Climatology Project (ISCCP) Dl data series, epoch superposition analysis of a sample of FD events is conducted. This analysis is conducted at a range of spatial scales from global, through 5° geomagnetic latitude bands to a global grid with 2.5° resolution. Resulting cloud anomalies are tested for significance using a randomized Monte Carlo experiment. The results indicate a small but significant (at 0.001 probability level) decline in the global proportion of cloud cover (of up to 1.4%) immediately prior to and following FD events. Analysis of data averaged over geomagnetic latitude (φ) bands reveals that significant cloud anomalies are concentrated in the high latitudes. A substantial (small) decline in cloud cover occurs at Southern (Northern) Hemisphere polar latitudes and is accompanied by a small but significant increase near φ = 30°N. The high-latitude anomalies occur largely in the high-level cloud and are particularly pronounced (up to −30%) in the uppermost cloud (occurring at 10–180 mbar) over Antarctica. In contrast, analysis using a sample of FD events associated with solar proton events shows no statistically significant cloud anomalies. A discussion of possible explanations of the results is provided
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Galactic cosmic ray modulation near the heliospheric current sheet
No full textGalactic cosmic rays (GCRs) are modulated by the heliospheric magnetic field (HMF) both over decadal time scales (due to long-term, global HMF variations), and over time scales of a few hours (associated with solar wind structures such as coronal mass ejections or the heliospheric current sheet, HCS). Due to the close association between the HCS, the streamer belt, and the band of slow solar wind, HCS crossings are often associated with corotating interaction regions where fast solar wind catches up and compresses slow solar wind ahead of it. However, not all HCS crossings are associated with strong compressions. In this study we categorize HCS crossings in two ways: Firstly, using the change in magnetic polarity, as either away-to-toward (AT) or toward-to-away (TA) magnetic field directions relative to the Sun and, secondly, using the strength of the associated solar wind compression, determined from the observed plasma density enhancement. For each category, we use superposed epoch analyses to show differences in both solar wind parameters and GCR flux inferred from neutron monitors. For strong-compression HCS crossings, we observe a peak in neutron counts preceding the HCS crossing, followed by a large drop after the crossing, attributable to the so-called ‘snow-plough’ effect. For weak-compression HCS crossings, where magnetic field polarity effects are more readily observable, we instead observe that the neutron counts have a tendency to peak in the away magnetic field sector. By splitting the data by the dominant polarity at each solar polar region, we find that the increase in GCR flux prior to the HCS crossing is primarily from strong compressions in cycles with negative north polar fields due to GCR drift effects. Finally, we report on unexpected differences in GCR behavior between TA weak compressions during opposing polarity cycles
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