VERITAS Observations of the Galactic Center Region at Multi-TeV Gamma-Ray Energies

Abstract

The Galactic Center (GC) region hosts a variety of powerful astronomical sources and rare astrophysical processes that emit a large flux of non-thermal radiation. The inner 375 pc x 600 pc region, called the Central Molecular Zone, is home to the supermassive black hole Sagittarius A*, massive cloud complexes, and particle accelerators such as supernova remnants. We present the results of our improved analysis of the very-high-energy (VHE) gamma-ray emission above 2 TeV from the GC using 125 hours of data taken with the VERITAS imaging-atmospheric Cherenkov telescope between 2010 and 2018. The central source VER J1745-290, consistent with the position of Sagittarius A*, is detected at a significance of 38 standard deviations above the background level $(38\sigma )$, and we report its spectrum and light curve. Its differential spectrum is consistent with a power law with exponential cutoff, with a spectral index of $2.12_{-0.17}^{+0.22}$, a flux normalization at 5.3 TeV of $1.27_{-0.23}^{+0.22}\times 10^{-13}$ TeV-1 cm-2 s-1, and cutoff energy of $10.0_{-2.0}^{+4.0}$ TeV. We also present results on the diffuse emission near the GC, obtained by combining data from multiple regions along the GC ridge which yield a cumulative significance of $9.5\sigma$. The diffuse GC ridge spectrum is best fit by a power law with a hard index of 2.19 $\pm$ 0.20, showing no evidence of a cutoff up to 40 TeV. This strengthens the evidence for a potential accelerator of PeV cosmic rays being present in the GC. We also provide spectra of the other sources in our field of view with significant detections, composite supernova remnant G0.9+0.1 and HESS J1746-285.

19 pages, 8 figures, Accepted for publication in Astrophysical Journal

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• Ultra-High-Energy Gamma-Ray Astronomy
• Constraints on late-forming exploding black holes
• VTSCat: The VERITAS Catalog of Gamma-Ray Observations
• Galactic center gamma-ray production by cosmic rays from stellar winds and Sgr A East
• Multi-TeV dark matter density in the inner Milky Way halo: spectral and dynamical constraints
• Cosmic rays cannot explain the high ionisation rates in the Galactic centre
• Chandra X-ray Measurement of Gas-phase Heavy Element Abundances in the Central Parsec of the Galaxy
• Multi-Wavelength Observation Campaign of the TeV Gamma-Ray Binary HESS J0632+057 with NuSTAR, VERITAS, MDM, and Swift
• Cosmic ray transport and acceleration with magnetic mirroring
• Impact of anisotropic cosmic-ray transport on the gamma-ray signatures in the Galactic Center
• Modeling the Galactic center gamma-ray emission with more realistic cosmic-ray dynamics
• Constraints on Axion-like Particles from the gamma-ray observation of the Galactic Center
• Search for the Galactic accelerators of Cosmic-Rays up to the Knee with the Pevatron Test Statistic
• HESS J1745$-$290 spectrum explained by a transition in the diffusion regime of PeV cosmic rays in the Sgr A* accretion flow
• Constraints on the origins of the Galactic neutrino flux
• The Very Energetic Radiation Imaging Telescope Array System (VERITAS)
• Dark Matter spikes around Sgr A* in $\gamma$-rays
• New Hard X-Ray and Multiwavelength Study of the PeVatron Candidate PWN G0.9+0.1 in the Galactic Center Region
• Modeling the shadow of Sgr A* through an eclipsing black hole
• High Energy Emission from the Galactic Center
• Search for long-term variability of HESS J1745-290
• Accelerated protons produced by magnetic Penrose process in Sgr A*
• Prospects for Observing the Microquasar SS 433 with the LACT Array