Observation of TeV Gamma Rays from the Fermi Bright Galactic Sources with the Tibet Air Shower Array

TL;DR

This study reports the first northern sky survey of Fermi bright Galactic sources in the TeV range, revealing significant correlations with TeV gamma-ray excesses and associations with pulsars and Milagro-detected sources.

Contribution

It presents the first TeV gamma-ray observations of Fermi bright Galactic sources using the Tibet-III array, establishing their statistical significance and associations with known TeV sources.

Findings

7 sources show >2 sigma excess, with a low chance probability of 3.8 x 10^-6.

All 7 sources are associated with pulsars.

6 sources coincide with Milagro >=3 sigma sources at 35 TeV.

Abstract

Using the Tibet-III air shower array, we search for TeV gamma-rays from 27 potential Galactic sources in the early list of bright sources obtained by the Fermi Large Area Telescope at energies above 100 MeV. Among them, we observe 7 sources instead of the expected 0.61 sources at a significance of 2 sigma or more excess. The chance probability from Poisson statistics would be estimated to be 3.8 x 10^-6. If the excess distribution observed by the Tibet-III array has a density gradient toward the Galactic plane, the expected number of sources may be enhanced in chance association. Then, the chance probability rises slightly, to 1.2 x 10^-5, based on a simple Monte Carlo simulation. These low chance probabilities clearly show that the Fermi bright Galactic sources have statistically significant correlations with TeV gamma-ray excesses. We also find that all 7 sources are associated with pulsars, and 6 of them are coincident with sources detected by the Milagro experiment at a significance of 3 sigma or more at the representative energy of 35 TeV. The significance maps observed by the Tibet-III air shower array around the Fermi sources, which are coincident with the Milagro >=3sigma sources, are consistent with the Milagro observations. This is the first result of the northern sky survey of the Fermi bright Galactic sources in the TeV region.