378 research outputs found
Variations in the propagation of UH-nuclei
Calculations of the propagation of UH-nuclei were improved by extending the number of individual nuclides considered, and by using more recent evaluations of the rigidity dependence of the escape length, the possible source composition, and altered cross sections. The effects of using different expressions for the dependence of abundances on first ionization potentials (FIP) are outlined. The sensitivity of the calculated elemental abundances to the various changes made in the propagation assumptions are discussed
Interactions of heavy nuclei, Kr, Xe and Ho, in light targets
Over the past few years, the HEAO-3 measurements of the abundances of ultra-heavy cosmic ray nuclei (Z 26) at earth have been analyzed. In order to interpret these abundances in terms of a source composition, allowance must be made for the propagation of the nuclei in the interstellar medium. Vital to any calculation of the propagation is a knowlege of the total and partial interaction cross sections for these heavy nuclei on hydrogen. Until recently, data on such reactions have been scarce. However, now that relativistic heavy ion beams are available at the LBL Bevalac, some of the cross sections of interest can be measured at energies close to those of the cosmic ray nuclei being observed. During a recent calibration at the Bevalac of an array similar to the HEAO-C3 UH-nuclei detector, targets of raphite (C), polyethylene (CH2), and aluminum were exposed to five heavy ion beams ranging in charge (Z) from 36 to 92. Total and partial charge changing cross sections for the various beam nuclei on hydrogen can be determined from the measured cross sections on C and CH2, and will be applied to the propagation problem. The cross sections on Al can be used to correct the abundances of UH cosmic rays observed in the HEAO C-3 detector for interactions in the detector itself
The Abundances of Ultraheavy Elements in the Cosmic Radiation
Analysis of a new, higher resolution data set from the Heavy Nuclei Experiment on
the HEA0-3 spacecraft has yielded the cosmic ray abundances relative to iron of oddeven
element pairs with atomic number, Z, in the range 33≤Z≤60. The abundances are
consistent with a solar-system source provided an allowance is made for a source
fraetionation based on first ionization potential (FIP). However, extending this analysis·
to element groups with Z>60, we find enhancements of the Pt group (74≤Z≤80)
abundance relative to the solar system and a corresponding increase in the largely
secondary nuclei in the range 62≤Z≤73, in agreement with recent Ariel-6 results. These
abundances suggest an enhancement of the r-process contribution to the source of the
Z > 60 nuclei
Mrk 421, Mrk 501, and 1ES 1426+428 at 100 GeV with the CELESTE Cherenkov Telescope
We have measured the gamma-ray fluxes of the blazars Mrk 421 and Mrk 501 in
the energy range between 50 and 350 GeV (1.2 to 8.3 x 10^25 Hz). The detector,
called CELESTE, used first 40, then 53 heliostats of the former solar facility
"Themis" in the French Pyrenees to collect Cherenkov light generated in
atmospheric particle cascades. The signal from Mrk 421 is often strong. We
compare its flux with previously published multi-wavelength studies and infer
that we are straddling the high energy peak of the spectral energy
distribution. The signal from Mrk 501 in 2000 was weak (3.4 sigma). We obtain
an upper limit on the flux from 1ES 1426+428 of less than half that of the Crab
flux near 100 GeV. The data analysis and understanding of systematic biases
have improved compared to previous work, increasing the detector's sensitivity.Comment: 15 pages, 14 figures, accepted to A&A (July 2006) August 19 --
corrected error in author lis
Release of Nuclei from Relativistic Nucleus-Nucleus Interactions
We have examined relativistic nuclei of iron, krypton, xenon, holmium and
gold, accelerated to maximum rigidity at the LBL Bevalac, interacting with targets of aluminum,
carbon and polyethylene. For each projc*:tile and target combination we determined the total and
partial charge changing cross-sections. From these measurements we have developed a new
representation of the dependence of the total charge changing cross-sections on beam and target
charge. We have also identified simple representations of the variation of the partial cross-sections
with the charge of the produced fragments and shown that they are dependent on the charge and
energy of the beam
The TeV spectrum of H1426+428
The BL Lac object H1426+428 was recently detected as a high energy gamma-ray
source by the VERITAS collaboration (Horan et al. 2002). We have reanalyzed the
2001 portion of the data used in the detection in order to examine the spectrum
of H1426+428 above 250 GeV. We find that the time-averaged spectrum agrees with
a power law of the shape dF/dE = 10^(-7.31 +- 0.15(stat) +- 0.16(syst)) x
E^(-3.50 +- 0.35(stat) +- 0.05(syst)) m^(-2)s^(-1)TeV^(-1) The statistical
evidence from our data for emission above 2.5 TeV is 2.6 sigma. With 95% c.l.,
the integral flux of H1426+428 above 2.5 TeV is larger than 3% of the
corresponding flux from the Crab Nebula. The spectrum is consistent with the
(non-contemporaneous) measurement by Aharonian et al. (2002) both in shape and
in normalization. Below 800 GeV, the data clearly favours a spectrum steeper
than that of any other TeV Blazar observed so far indicating a difference in
the processes involved either at the source or in the intervening space.Comment: LaTeX, 8 pages, 4 figures, accepted for publication in Ap
Interactions of Heavy Nuclei, Kr, Xe and Ho, in Light Targets
Over the past few years, we have been analyzing the
HEAO-3 measurements of the abundances of ultra-heavy cosmic ray nuclei
(Z>26) at earth. In order to interpret these abundances in terms of a
source composition, allowance must be made for the propagation of the
nuclei in the interstellar medium. Vital to any calculation of the
propagation is a knowledge of the total and partial interaction cross
sections for these heavy nuclei on hydrogen. Until recently, data on
such reactions have been scarce, and we have relied on the semiempirical
formalism of Silberberg and Tsao to predict the partial cross
sections. However, now that relativistic heavy ion beams are available
at the LBL Bevalac, some of the cross sections of interest can be
measured at energies close to those of the cosmic ray nuclei being
observed
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