The GeV-TeV Connection in Galactic gamma-ray sources

TL;DR

This paper investigates the relationship between GeV and TeV gamma-ray sources in our galaxy, revealing few common sources, constraining spectral models, and predicting future observations with the GLAST mission.

Contribution

It provides the first systematic comparison of GeV and TeV gamma-ray sources, highlighting spectral cutoffs and proposing predictions for upcoming gamma-ray observations.

Findings

Few sources are common between GeV and TeV catalogs.

Spectral cutoffs are suggested in the 10-100 GeV range.

VHE upper limits constrain simple spectral extrapolations.

Abstract

Recent observations with atmospheric Cherenkov telescope systems such as H.E.S.S. and MAGIC have revealed a large number of new sources of very-high-energy (VHE) gamma-rays from 100 GeV - 100 TeV, mostly concentrated along the Galactic plane. At lower energies (100 MeV - 10 GeV) the satellite-based instrument EGRET revealed a population of sources clustering along the Galactic Plane. Given their adjacent energy bands a systematic correlation study between the two source catalogues seems appropriate. Here, the populations of Galactic sources in both energy domains are characterised on observational as well as on phenomenological grounds. Surprisingly few common sources are found in terms of positional coincidence and spectral consistency. These common sources and their potential counterparts and emission mechanisms will be discussed in detail. In cases of detection only in one energy band, for the first time consistent upper limits in the other energy band have been derived. The EGRET upper limits are rather unconstraining due to the sensitivity mismatch to current VHE instruments. The VHE upper limits put strong constraints on simple power-law extrapolation of several of the EGRET spectra and thus strongly suggest cutoffs in the unexplored energy range from 10 GeV - 100 GeV. Physical reasons for the existence of cutoffs and for differences in the source population at GeV and TeV energies will be discussed. Finally, predictions will be derived for common GeV - TeV sources for the upcoming GLAST mission bridging for the first time the energy gap between current GeV and TeV instruments.