Search for long-term variability of HESS J1745-290

TL;DR

This study analyzed 16 years of H.E.S.S. data on the Galactic center's HESS J1745-290 source, finding no significant long-term variability or flux changes exceeding 30%.

Contribution

It presents a novel 3D maximum-likelihood analysis separating the source from diffuse emission, enabling precise long-term variability assessment.

Findings

No long-term or yearly variability detected.

Ruled out flux variations larger than 30% over 16 years.

Provided sensitivity estimates for future variability detection.

Abstract

At the center of our Galaxy lies the bright {\gamma}-ray point-like source HESS J1745-290, which is compatible in position with Sgr A star, although an association between the two remains uncertain. Using data obtained between 2004 and 2019 with the High Energy Stereoscopic System (H.E.S.S.) on the Galactic center region, we studied the variability of HESS J1745-290 over 353 hours of observations collected over 16 years, representing the largest dataset gathered yet on this region at TeV energies. We performed a 3D maximum-likelihood analysis of the central source and the diffuse {\gamma}-ray emission in the Galactic center region. This analysis allowed us to extract the spectral and morphological intrinsic behavior of the two components. By performing this analysis on an annual basis, we derived the light curve of HESS J1745-290 and the diffuse emission over the past 16 years. The 3D maximum-likelihood analysis method allowed us to separate the central source from the overlapping diffuse emission, enabling a recalibration of the former by the latter and alleviating some of the systematic effects. We find no long-term or yearly variability. We also provide an estimate of the sensitivity of H.E.S.S. to variation of this specific source over 16 years. We rule out any yearly gamma-ray flux variation of this source larger than 30 percent, as well as any linear flux variation exceeding 30% over this time period.