Very-high energy observations of the Galactic center region by VERITAS in 2010-2012

TL;DR

This paper reports three years of VERITAS observations of the Galactic center, detecting very-high-energy gamma rays with high significance and analyzing the energy spectrum to explore potential emission mechanisms.

Contribution

The study provides the first extensive VERITAS data set on the Galactic center at large zenith angles, with a high-significance detection and spectral analysis relevant for understanding gamma-ray sources.

Findings

Detection of the Galactic center at >18 sigma above 2.5 TeV

Energy spectrum compatible with multiple emission models

Provides constraints for future high-energy gamma-ray studies

Abstract

The Galactic center is an interesting region for high-energy (0.1-100 GeV) and very-high-energy (E > 100 GeV) gamma-ray observations. Potential sources of GeV/TeV gamma-ray emission have been suggested, e.g., the accretion of matter onto the supermassive black hole, cosmic rays from a nearby supernova remnant (e.g. SgrA East), particle acceleration in a plerion, or the annihilation of dark matter particles. The Galactic center has been detected by EGRET and by Fermi/LAT in the MeV/GeV energy band. At TeV energies, the Galactic center was detected with moderate significance by the CANGAROO and Whipple 10 m telescopes and with high significance by H.E.S.S., MAGIC, and VERITAS. We present the results from three years of VERITAS observations conducted at large zenith angles resulting in a detection of the Galactic center on the level of 18 standard deviations at energies above ~2.5TeV. The energy spectrum is derived and is found to be compatible with hadronic, leptonic and hybrid emission models discussed in the literature. Future, more detailed measurements of the high-energy cutoff and better constraints on the high-energy flux variability will help to refine and/or disentangle the individual models.