Gamma ray sources observation with the ARGO-YBJ detector

Abstract

"In this paper we report on the observations of. TeV gamma ray sources performed by the air shower detector. ARGO-YBJ. The objects studied in this work are. the blazar Markarian 421 and the extended galactic source. MGROJ1908+06, monitored during 2 years of operation.. Mrk421 has been detected by ARGO-YBJ with a statistical. significance of 11 standard deviations. The observed. TeV emission was highly variable, showing large enhancements. of the flux during active periods. The study of the. spectral behaviour during flares revealed a positive correlation. of the hardness with the flux, as already reported in the. past by the Whipple telescope, suggesting that this is a long. term property of the source.. ARGO-YBJ observed a strong correlation between TeV. gamma rays and the X-ray flux measured by RXTM\/ASM. and SWIFT\/BAT during the whole period, with a time lag. compatible with zero, supporting the one-zone SSC model to. describe the emission mechanism.. MGROJ1908+06 has been detected by ARGO-YBJ with. 5 standard deviation of significance. From our data. the source appears extended and the measured extension is. ext=0.48+0.26. −0.28, in agreement with a previous HESS observation.. The average flux is in marginal agreement with that. reported by MILAGRO, but significantly higher than that obtained. by HESS, suggesting a possible flux variability.