Prospects for Observing the Microquasar SS 433 with the LACT Array

TL;DR

This study assesses the scientific potential of the LACT Cherenkov telescope array for probing the microquasar SS 433 via detailed simulations with instrument response functions. It finds that a $\sim30$ hour campaign can yield a $\sim5\sigma$ detection of the system's eastern and western jets in the $10$–$300$ TeV band, enabling high-resolution imaging of extended jet structures. The analysis indicates LACT can discriminate between spectral models derived from H.E.S.S. and LHAASO data and can begin to isolate a central hadronic emission component after tens of hours at tens of TeV, with longer exposures needed at higher energies due to photon statistics. Overall, LACT is shown to offer a powerful combination of angular resolution and energy reach to advance understanding of particle acceleration in microquasar jets and to complement LHAASO observations in the ultra-high-energy regime.

Abstract

We investigate the observational capabilities of the upcoming LACT Cherenkov telescope array for the microquasar SS 433 through detailed simulations. Our results indicate that a detection significance of about 5-sigma can be achieved with approximately 30 hours of observation. The array is capable of spatially resolving the eastern and western jets, and-based on the LHAASO spectral and morphological findings-can distinguish the central hadronic component after roughly 100 h of observation. We further examine its ability to distinguish between the H.E.S.S. and LHAASO spectral models. These findings demonstrate LACT's strong potential to probe the spatial and spectral structure of SS 433 at very high energies, providing valuable insights into particle acceleration in PeVatrons and the radiation mechanisms of microquasars.

Figures (7)

• Figure 1: Angular resolution and effective area of the LACT array as functions of energy for both large-zenith-angle($60^{\circ}$) and small-($20^{\circ}$) observation modes. The results are obtained from Monte-Carlo simulations based on the optimized array layout.
• Figure 2: Cumulative observable time of SS 433 from the LHAASO site between October and April. The curves show visibility under two zenith-angle ranges (0°–50° and 50°–70°). Nighttime is defined by the Sun’s altitude below –18°.
• Figure 3: Top: A counts map of the SS 433 eastern and western jets from an 100-hour simulated observation. Bottom: The corresponding significance map in SS 433 region, where the significance is represented as the square root of the TS value.
• Figure 4: The detection significance of the SS 433 eastern and western jets as a function of observation time. The red dashed line indicates the $3\sigma$ threshold. Each data point represents the mean of total simulations, with error bars corresponding to the 68% confidence interval. The star reprents the result of H.E.S.S.(east jet, 7.8$\sigma$)hess2024acceleration.
• Figure 5: Simulated LACT counts maps for SS 433 based on the three-source model inferred from LHAASO observations. From top to bottom: photon energies above 30 TeV, 50 TeV, and 100 TeV. The red crosses mark the positions of the two jet regions, while the cyan circle indicates the location and approximate extent of the extended source reported by LHAASO. All maps correspond to one 100-hour observation in the 60°-zenith-angle mode using the same IRFs. At energies above 100 TeV, the very low photon counts lead to noticeable irregular fluctuations dominated by the background.