H.E.S.S. observations of SN 2024ggi

TL;DR

This study reports H.E.S.S. TeV gamma-ray observations of SN 2024ggi, a nearby core-collapse supernova interacting with a dense circumstellar medium. About 30 hours of data were collected in the first month after explosion, yielding 95% confidence level upper limits on the TeV flux and corresponding luminosities, with no significant detection. The early-time limit rules out bright gamma-ray emission predicted by some hadronic models, while later limits are compatible with wind densities inferred from optical data. The results place constraints on cosmic-ray acceleration and the gamma-ray detectability of interaction-powered supernovae, emphasizing the roles of distance and attenuation in shaping the very-high-energy signal.

Abstract

Supernova (SN) explosions interacting with dense circumstellar medium are considered to be very promising sites for efficient cosmic-ray (CR) acceleration and subsequent emission of neutral-pion-decay gamma rays. These environments share similarities with already detected gamma-ray novae, but with much greater available energy content, so it is important to characterize their emission in the very-high-energy range. We present the results of H.E.S.S. observations of one such candidate source - SN 2024ggi, located in NGC 3621 at a distance of 7.24 Mpc. A total of 30 hours of data, gathered throughout a month of post-explosion observations, provide flux upper limits that are used to constrain source parameters, offering meaningful insights for theoretical predictions. We exclude bright gamma-ray emission in the first day after explosion, and later upper limits are consistent with wind densities derived from optical observations.

Figures (5)

• Figure 1: All selected H.E.S.S. observations of SN 2024ggi spanning the whole observation period, together with the optical lightcurve from the ATLAS forced photometry server Tonry_2018atlas_transientsforcedphotoserver.
• Figure 2: Excess count map (left panel), significance map (middle panel), and significance distribution with a Gaussian fit (right panel), computed from all the selected H.E.S.S. CT1--4 observations of SN 2024ggi.
• Figure 3: 95% C. L. differential photon flux upper limits, derived from all the selected H.E.S.S. observations of SN 2024ggi. Central telescope results (CT5) are shown in light green, and the results from the CT1--4 array are shown in dark green.
• Figure 4: 95% C. L. differential photon flux upper limits at a reference energy of 1.22 TeV across the whole time of H.E.S.S. SN 2024ggi observations by the CT1--4 telescope array.
• Figure 5: Comparison of the luminosity upper limits derived from H.E.S.S. CT1--4 observations of SN 2024ggi to the theoretical model from Brose_2022 with (light green) and without (dark green) the effect of $\gamma \gamma$ absorption included, as well as the analytical model from Tatischeff_2009, applied to a possible range of mass-loss rate values (blue).