Effect of the aerosol profiles on shower reconstruction: a general and seasonal study

MARÍA ISABEL MICHELETTI; DIEGO MELO

PUBLICACION INTERNA DE LA COLABORACION INTERNACIONAL AUGER

PUBLICACION INTERNA DE LA COLABORACION INTERNACIONAL AUGER

Año: 2007 p. 1 - 24

Cosmic ray shower hybrid events detected at the Auger Observatory have been reconstructed using, for the evaluation of the transmittance of the light emitted as they cross the atmosphere, aerosols measured in the field, in one case, and a parametric aerosols profile, in another case. This analysis was performed using all cosmic ray showers hybrid data –registered at the FD eyes placed at Los Leones and Coihueco– corresponding to the days that have aerosol profiles measured at the Observatory site. These days belong to the period that goes from April 2004 to August 2006. A general and a detailed seasonal study were done for this period. With the parametric profile used at present by the Auger Collaboration reconstruction software, as an average of the atmospheric conditions at the site of the Observatory, the mean percent relative difference in the reconstructed energy, obtained by using it or by using the measured aerosols, turns to be, at both of the FD eyes, less or equal than 4 % for the complete analyzed period but fluctuates within a range of 8 % for the different seasons. A correct evaluation of the energy of the incident particle is necessary for obtaining the cosmic rays energy spectrum. The mean difference in the reconstructed atmospheric depth where the shower reaches its maximum development, Xmax, is less than 2 g/cm2 for the complete period but fluctuates within a range of 11 g/cm2 for the different seasons. We analyzed the variation of the mean value of Xmax as a function of log10(E), of importance in composition studies. This variation turns out to be different for the different seasons. We also analyzed the variation of the mean percent relative difference of the energy as a function of log10(E), which also depends on the seasons. The use of the parametric Mie profile currently accepted for the site of the Observatory overestimate the energy at the cleanest season (autumn) and underestimate the energy at the dirtiest one (summer).