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 nonthermal radiation. The inner 375 pc × 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 (SNRs). We present the results of our improved analysis of the very-high-energy gamma-ray emission above 2 TeV from the GC using 125 hr of data taken with the Very Energetic Radiation Imaging Telescope Array System imaging-atmospheric Cerenkov 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 (38σ), 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 10 0.23 0.22 13 TeV −1 cm −2 s −1 , and cutoff energy of -+ 10.0 2.0 4.0TeV. 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 9.5σ. The diffuse GC ridge spectrum is best fit by a power law with a hard index of 2.19 ± 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 SNR G0.9+0.1, and HESS J1746-285.

Multi-TeV dark matter density in the inner Milky Way halo: spectral and dynamical constraints

“…In figure 12 (upper right panel) we compare our fit of the Ridge region with Fermi-LAT, MAGIC and VERITAS data [93]. Although the gamma-ray spectra is well fitted by our model, the best fit for the J-factor favors the hypothesis of an astrophysical gamma-ray emission for this region.…”

Dark matter spikes around Sgr A* in γ-rays

“…Recent years have seen the first detections [5][6][7] of multi-TeV γ-rays from the region of the supermassive black hole at the center of the Milky Way galaxy, Sgr A*, and these will be improved and extended in the near future [8][9][10]. What can one learn from these observations, about DM particle properties and about the DM mass distribution in the Milky Way galaxy?…”

“…Over the last decade, we have successfully detected multi-TeV γ-rays emanating from Sgr A* for the first time using telescopes such as H.E.S.S. [5], VERITAS [6], and MAGIC [7]. With advancements in detectors, such as LHAASO [8] and the upcoming CTA [9,10], we anticipate JCAP08(2023)063 further advancements in this area.…”

Impact of Anisotropic Cosmic-Ray Transport on the Gamma-Ray Signatures in the Galactic Center

“…The Galactic center (GC) is one of the most extreme and closeby astrophysical environments and is of particular interest for studies of nonthermal processes. The GC has been studied in all wavelengths from the radio (Heywood et al 2022) to high- (Ajello et al 2016;Di Mauro 2021) and very high energy (VHE) γ-rays (Abramowski et al 2016;Abdalla et al 2018;Acciari et al 2020;Adams et al 2021). The observed outflows at γ-ray (Ackermann et al 2014), X-ray (Sofue 2000), microwave (Finkbeiner 2004;Planck Collaboration et al 2013), and radio wavelengths (Pedlar et al 1989) as well as small-scale structures such as nonthermal filaments and molecular clouds (see Henshaw et al 2023, for a review) are in need of proper modeling.…”