Detection of variable VHE gamma-ray emission from the extra-galactic gamma-ray binary LMC P3

TL;DR

This study reports the first detection of variable very-high-energy gamma-ray emission from the extragalactic gamma-ray binary LMC P3, showing orbital modulation and anti-correlation with high-energy gamma-ray emission, establishing it as the most luminous gamma-ray binary.

Contribution

The paper presents the first VHE gamma-ray detection of LMC P3 and demonstrates its orbital variability and anti-correlation with HE emission, expanding understanding of extragalactic gamma-ray binaries.

Findings

VHE gamma-ray emission detected with 6.4 sigma significance.

Emission shows phase-locked variability with the orbital period.

LMC P3 is the most luminous gamma-ray binary known.

Abstract

Context. Recently, the high-energy (HE, 0.1-100 GeV) $\gamma$-ray emission from the object LMC P3 in the Large Magellanic Cloud (LMC) has been discovered to be modulated with a 10.3-day period, making it the first extra-galactic $\gamma$-ray binary. Aims. This work aims at the detection of very-high-energy (VHE, >100 GeV) $\gamma$-ray emission and the search for modulation of the VHE signal with the orbital period of the binary system. Methods. LMC P3 has been observed with the High Energy Stereoscopic System (H.E.S.S.); the acceptance-corrected exposure time is 100 h. The data set has been folded with the known orbital period of the system in order to test for variability of the emission. Energy spectra are obtained for the orbit-averaged data set, and for the orbital phase bin around the VHE maximum. Results. VHE $\gamma$-ray emission is detected with a statistical significance of 6.4 $\sigma$. The data clearly show variability which is phase-locked to the orbital period of the system. Periodicity cannot be deduced from the H.E.S.S. data set alone. The orbit-averaged luminosity in the $1-10$ TeV energy range is $(1.4 \pm 0.2) \times 10^{35}$ erg/s. A luminosity of $(5 \pm 1) \times 10^{35}$ erg/s is reached during 20% of the orbit. HE and VHE $\gamma$-ray emissions are anti-correlated. LMC P3 is the most luminous $\gamma$-ray binary known so far.