The Beijing Huairou extensive air shower (EAS) array has been operating sincc March 1988. Using data observed during the period from April 1991 through January 1993, a burst of 12 EAS events were observed within Z-minute interval beginning a t 4:41'54'' ante meridiem on December 30 1991 universal time, while only 2 EAS events on average would have been expected during such time interval.
Using the data taken from Tibet II High Density (HD) Array (1997 February-1999 and Tibet-III array (1999 November-2005, our previous northern sky survey for TeV γ−ray point sources has now been updated by a factor of 2.8 improved statistics. From 0.0• to 60.0 • in declination (Dec) range, no new TeV γ−ray point sources with sufficiently high significance were identified while the well-known Crab Nebula and Mrk421 remain to be the brightest TeV γ−ray sources within the field of view of the Tibet air shower array. Based on the currently available data and at the 90% confidence level (C.L.), the flux upper limits for different power law index assumption are re-derived, which are approximately improved by 1.7 times as compared with our previous reported limits.
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