47 Tuc was the first globular cluster observed to be $gamma$-ray bright, with the $gamma$-rays being attributed to a population of unresolved millisecond pulsars (MSPs). Recent kinematic data, combined with detailed simulations, appears to be consistent with the presence of an intermediate mass black hole (IMBH) at the centre of 47 Tuc. Building upon this, we analyse 9 years of textit{Fermi}-LAT observations to study the spectral properties of 47 Tuc with unprecedented accuracy and sensitivity. This 9-year $gamma$-ray spectrum shows that 47 Tucs $gamma$-ray flux cannot be explained by MSPs alone, due to a systematic discrepancy between the predicted and observed flux. Rather, we find a significant preference (TS $=40$) for describing 47 Tucs spectrum with a two source population model, consisting of an ensemble of MSPs and annihilating dark matter (DM) with an enhanced density around the IMBH, when compared to an MSP-only explanation. The best-fit DM mass of 34 GeV is essentially the same as the best-fit DM explanation for the Galactic centre excess when assuming DM annihilation into $bbar{b}$ quarks. Our work constitutes the first possible evidence of dark matter within a globular cluster.
تحميل البحث