Speaker
Description
We report on gamma-ray observations of the binary black hole (BBH) merger candidate S241125n, detected by the LIGO-Virgo-KAGRA Collaboration during the O4b observing run. Follow-up observations were performed with the MAGIC telescopes and the Large-Sized Telescope prototype (LST-1) of the Cherenkov Telescope Array Observatory. S241125n is of particular interest due to its temporal and spatial coincidence with a sub-threshold short-duration burst detected by Swift/BAT, Swift/XRT, and the Einstein Probe/FXT, offering a rare opportunity to probe potential electromagnetic counterparts to a BBH merger.
The observations were conducted under suboptimal atmospheric conditions, with the presence of cloud coverage significantly impacting data quality. To address this problem, LIDAR-based atmospheric measurements were included into dedicated Monte Carlo simulations of extensive air showers and Cherenkov light emission. Out of ~4 hours of LST-1 observations (including ~3.4 hours in joint configuration with the MAGIC telescopes), ~1 hour of data was retained, limited to selected runs where conditions allowed for reliable instrument response calibration. The spectral energy distribution and light curve were derived for reconstructed energies above 500 GeV. This approach ensures a reliable analysis despite adverse conditions and highlights the importance of real-time atmospheric monitoring for ground-based gamma-ray astronomy.