352 research outputs found
Highlights from the ARGO-YBJ experiment
The ARGO-YBJ experiment is in stable data taking since November 2007 at the YangBaJing Cosmic Ray Laboratory (Tibet, P.R. China, 4300m a.s.l., 606 g/cm2). The results from the first 3.5 years of operation are reviewed
Evolution of the cosmic ray anisotropy above 10^{14} eV
The amplitude and phase of the cosmic ray anisotropy are well established
experimentally between 10^{11} eV and 10^{14} eV. The study of their evolution
into the energy region 10^{14}-10^{16} eV can provide a significant tool for
the understanding of the steepening ("knee") of the primary spectrum. In this
letter we extend the EAS-TOP measurement performed at E_0 around 10^{14} eV, to
higher energies by using the full data set (8 years of data taking). Results
derived at about 10^{14} and 4x10^{14} eV are compared and discussed. Hints of
increasing amplitude and change of phase above 10^{14} eV are reported. The
significance of the observation for the understanding of cosmic ray propagation
is discussed.Comment: 4 pages, 3 figures, accepted for publication on ApJ Letter
Results on high-energy cosmic rays by EAS-TOP at Gran Sasso
Very High-Energy cosmic rays have to be studied through the
ground-based detectors of the Extensive Air Showers (EAS) that they produce in the atmosphere. The main measurements to be performed are of: primary energy spectra, composition, anisotropies, «neutral primary» astronomy, and interaction properties. This requires complete detectors of all the EAS components, and for this purpose the EAS-TOP array has been constructed at Campo Imperatore (2000 m
a.s.l.) on top of the Gran Sasso underground laboratories. The array has been progressively going into operation since 1988. In this paper we present the status and performances of the different detectors, and the results obtained up to now on the different items under discussion
The cosmic ray primary composition in the "knee" region through the EAS electromagnetic and muon measurements at EAS-TOP
Abstract The evolution of the cosmic ray primary composition in the energy range 10 6 –10 7 GeV (i.e. the "knee" region) is studied by means of the e.m. and muon data of the Extensive Air Shower EAS-TOP array (Campo Imperatore, National Gran Sasso Laboratories). The measurement is performed through: (a) the correlated muon number ( N μ ) and shower size ( N e ) spectra, and (b) the evolution of the average muon numbers and their distributions as a function of the shower size. From analysis (a) the dominance of helium primaries at the knee, and therefore the possibility that the knee itself is due to a break in their energy spectrum (at E k He =(3.5±0.3)×10 6 GeV) are deduced. Concerning analysis (b), the measurement accuracies allow the classification in terms of three mass groups: light (p,He), intermediate (CNO), and heavy (Fe). At primary energies E 0 ≈10 6 GeV the results are consistent with the extrapolations of the data from direct experiments. In the knee region the obtained evolution of the energy spectra leads to: (i) an average steep spectrum of the light mass group ( γ p,He >3.1), (ii) a spectrum of the intermediate mass group harder than the one of the light component ( γ CNO ≃2.75, possibly bending at E k CNO ≈(6–7)×10 6 GeV), (iii) a constant slope for the spectrum of the heavy primaries ( γ Fe ≃2.3–2.7) consistent with the direct measurements. In the investigated energy range, the average primary mass increases from 〈ln A 〉=1.6–1.9 at E 0 ≃1.5×10 6 GeV to 〈ln A 〉=2.8–3.1 at E 0 ≃1.5×10 7 GeV. The result supports the standard acceleration and propagation models of galactic cosmic rays that predict rigidity dependent cut-offs for the primary spectra of the different nuclei. The uncertainties connected to the hadronic interaction model (QGSJET in CORSIKA) used for the interpretation are discussed
Temperature variations in the low stratosphere (50–200 hPa) monitored by means of the atmospheric muon flux
The dependence of the muon flux on the atmospheric parameters (pressure and temperature) is a well-known effect since long time ago. We have correlated the muon flux recorded by the electromagnetic detector of EAS-TOP with the atmospheric temperature (up to few hPa level) monitored by the radio-soundings of the ITAV—Aeronautica Militare at Pratica di Mare (Rome). A significant effect has
been observed when the muon flux is correlated with the atmospheric temperature in the region 50–200 hPa, as expected, since this is the region where the mesons of
first generation are produced. The technique has been applied to two short periods of strong temperature variations in the low stratosphere, showing that the temporal pattern of the temperature is fairly well reproduced by the variations of the muon flux. The main results of this analysis are presented
4.5 years multi-wavelength observations of Mrk 421 during the ARGO-YBJ and Fermi common operation time
We report on the extensive multi-wavelength observations of the blazar
Markarian 421 (Mrk 421) covering radio to gamma-rays, during the 4.5 year
period of ARGO-YBJ and Fermi common operation time, from August 2008 to
February 2013. In particular, thanks to the ARGO-YBJ and Fermi data, the whole
energy range from 100 MeV to 10 TeV is covered without any gap. In the
observation period, Mrk 421 showed both low and high activity states at all
wavebands. The correlations among flux variations in different wavebands were
analyzed. Seven large flares, including five X-ray flares and two GeV gamma-ray
flares with variable durations (3-58 days), and one X-ray outburst phase were
identified and used to investigate the variation of the spectral energy
distribution with respect to a relative quiescent phase. During the outburst
phase and the seven flaring episodes, the peak energy in X-rays is observed to
increase from sub-keV to few keV. The TeV gamma-ray flux increases up to
0.9-7.2 times the flux of the Crab Nebula. The behavior of GeV gamma-rays is
found to vary depending on the flare, a feature that leads us to classify
flares into three groups according to the GeV flux variation. Finally, the
one-zone synchrotron self-Compton model was adopted to describe the emission
spectra. Two out of three groups can be satisfactorily described using injected
electrons with a power-law spectral index around 2.2, as expected from
relativistic diffuse shock acceleration, whereas the remaining group requires a
harder injected spectrum. The underlying physical mechanisms responsible for
different groups may be related to the acceleration process or to the
environment properties.Comment: 17 pages, 9 figures, 5 tables, Accepted for publication in ApJ
The cosmic ray proton plus helium energy spectrum measured by the ARGO-YBJ experiment in the energy range 3-300 TeV
The ARGO-YBJ experiment is a full-coverage air shower detector located at the
Yangbajing Cosmic Ray Observatory (Tibet, People's Republic of China, 4300 m
a.s.l.). The high altitude, combined with the full-coverage technique, allows
the detection of extensive air showers in a wide energy range and offer the
possibility of measuring the cosmic ray proton plus helium spectrum down to the
TeV region, where direct balloon/space-borne measurements are available. The
detector has been in stable data taking in its full configuration from November
2007 to February 2013. In this paper the measurement of the cosmic ray proton
plus helium energy spectrum is presented in the region 3-300 TeV by analyzing
the full collected data sample. The resulting spectral index is . These results demonstrate the possibility of performing an accurate
measurement of the spectrum of light elements with a ground based air shower
detector.Comment: 18 pages, 8 figures, preprint submitted to Phys. Rev.
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