On the absolute value of the air-fluorescence yield

The absolute value of the air-fluorescence yield is a key parameter for the energy reconstruction of extensive air showers registered by fluorescence telescopes. In previous publications, we reported a detailed Monte Carlo simulation of the air-fluorescence generation that allowed the theoretical evaluation of this parameter. This simulation has been upgraded in the present work. As a result, we determined an updated absolute value of the fluorescence yield of 7.9+-2.0 ph/MeV for the band at 337 nm in dry air at 800 hPa and 293 K, in agreement with experimental values. We have also performed a critical analysis of available absolute measurements of the fluorescence yield with the assistance of our simulation. Corrections have been applied to some measurements to account for a bias in the evaluation of the energy deposition. Possible effects of other experimental aspects have also been discussed. From this analysis, we determined an average fluorescence yield of 7.04+-0.24 ph/MeV at the above conditions.Comment: Submitted to Astroparticle Physic

Comparison of available measurements of the absolute air-fluorescence yield and determination of its global average value

Experimental results of the absolute air-fluorescence yield are given very often in different units (photons/MeV or photons/m) and for different wavelength intervals. In this work we present a comparison of available results normalized to its value in photons/MeV for the 337 nm band at 1013 hPa and 293 K. The conversion of photons/m to photons/MeV requires an accurate determination of the energy deposited by the electrons in the field of view of the experimental set-up. We have calculated the energy deposition for each experiment by means of a detailed Monte Carlo simulation and the results have been compared with those assumed or calculated by the authors. As a result, corrections to the reported fluorescence yields are proposed. These corrections improve the compatibility between measurements in such a way that a reliable average value with uncertainty at the level of 5% is obtained.Comment: 13 pages, 6 figures. To appear in the Proocedings of the International Symposium on the Recent Progress of Ultra-high Energy Cosmic Ray Observations (UHECR2010), Nagoya, Japan, 201

The Small Contribution of Molecular Bremsstrahlung Radiation to the Air-Fluorescence Yield of Cosmic Ray Shower Particles

A small contribution of molecular Bremsstrahlung radiation to the air-fluorescence yield in the UV range is estimated based on an approach previously developed in the framework of the radio-detection of showers in the gigahertz frequency range. First, this approach is shown to provide an estimate of the main contribution of the fluorescence yield due to the de-excitation of the C $^3\Pi_{\mathrm{u}}$ electronic level of nitrogen molecules to the B $^3\Pi_{\mathrm{g}}$ one amounting to $Y_{[337]}=(6.05\pm 1.50)~$ MeV$^{-1}$ at 800 hPa pressure and 293 K temperature conditions, which compares well to previous dedicated works and to experimental results. Then, under the same pressure and temperature conditions, the fluorescence yield induced by molecular Bremsstrahlung radiation is found to be $Y_{[330-400]}^{\mathrm{MBR}}=0.10~$ MeV$^{-1}$ in the wavelength range of interest for the air-fluorescence detectors used to detect extensive air showers induced in the atmosphere by ultra-high energy cosmic rays. This means that out of $\simeq 175~$ photons with wavelength between 330 and 400 nm detected by fluorescence detectors, one of them has been produced by molecular Bremsstrahlung radiation. Although small, this contribution is not negligible in regards to the total budget of systematic uncertainties when considering the absolute energy scale of fluorescence detectors.Comment: 9 pages, 2 figures, accepted for publication in Astropart. Phys. arXiv admin note: text overlap with arXiv:1601.0055

The catalogue of OB associations in IC 1613

We present a catalogue of OB associations in IC 1613. Using an automatic and objective method (Battinelli's 1991 technique) 60 objects were found. The size distribution reveals a significant peak at about 60 parsecs if a distance modulus of 24.27 mag is assumed. Spatial distributions of the detected associations and H II regions are strongly correlated.Comment: 5 pages, 3 figures, A&A accepte