Speaker
Description
Very-high-energy (VHE) gamma-ray observations of the Galactic Center (GC) have placed stringent constraints on dark matter candidate models, including supersymmetric wino and higgsino scenarios, with sensitivities approaching the predictions of thermal relic models. The Large-Sized Telescopes (LSTs) of the next-generation gamma-ray facility, the Cherenkov Telescope Array Observatory (CTAO), which is scheduled to begin operation in the coming years, are expected to provide timely and critical opportunities for dark matter searches.
The first LST, LST-1, has been taking GC data since 2020 and has demonstrated its observational capability. Its field of view, about 4.5 deg in diameter, is relatively large compared with those of current-generation instruments of the same class, particularly those in the Northern Hemisphere, enhancing sensitivity to spatially extended emission. Owing to its location, LST-1 observes the GC at large zenith angles, where sensitivity at TeV energies increases by more than a factor of two, at the cost of raising the energy threshold to hundreds of GeV. The combination of these characteristics, the large field of view and the observations at large zenith angles, is currently unique and already gives LST-1 competitive reach for line-like dark matter searches, despite the limited exposure. However, these features generally lead to larger systematic uncertainties and pose analysis challenges. With the development of dedicated analysis schemes, LST-1 already enables high-sensitivity observations of TeV diffuse gamma rays across this region, even in a monoscopic configuration.
Using about 40 hours of GC data obtained with LST-1, we performed a search for VHE gamma-ray signals from dark matter annihilation, focusing on so-called monochromatic lines with the aim of identifying these narrow spectral features in the GC data. Systematic uncertainties in this analysis were evaluated using both dedicated simulations and off-source data. We found no significant line-like excess and derived upper limits on the dark matter annihilation cross section. In this contribution, we report the results of the LST-1 data analysis and discuss the prospects for the forthcoming LST array.
