Observation of PeV Gamma Rays from the Monogem Ring with the Tibet Air Shower Array

Abstract

We searched for steady PeV gamma-ray emission from the Monogem ring region with the Tibet air shower array from 1997 February to 2004 October. No evidence for statistically significant gamma-ray signals was found in a region 111$\degr$ $\le$ R.A. $<$ 114$\degr$, 12$\fdg$5 $\le$ decl. $<$ 15$\fdg$5 in the Monogem ring where the MAKET-ANI experiment recently claimed a positive detection of PeV high-energy cosmic radiation, although our flux sensitivity is approximately 10 times better than MAKET-ANI's. We set the most stringent integral flux upper limit at a 99% confidence level of 4.0 $\times$ 10${}^{-12}$ cm${}^{-2}$ s${}^{-1}$ sr${}^{-1}$ above 1 PeV on diffuse gamma rays extended in the 3${}^{\circ }$ $\times$ 3${}^{\circ }$ region.

13 pages 3figures, 1 table