Evidence for a Stellar Disruption by an Imbh in an Extragalactic Globular Cluster1

We report [O III] λ5007 Å and [N II] λ6583 Å emission from a globular cluster harboring the ultraluminous X-ray source (ULX) CXOJ033831.8-352604 in the Fornax elliptical galaxy NGC 1399. No accompanying Balmer emission lines are present in the spectrum. One possibility is that the forbidden lines emanate from X-ray illuminated debris of a star that has been tidally-disrupted by an intermediate-mass black hole (IMBH), with this debris also feeding the black hole leading to the observed X-ray emission. The line strengths indicate that the minimum size of the emitting region is ∼1015 cm, and if the 70 km s−1 half-widths of the emission lines represent rotation around the black hole, a minimum black hole mass of 1000 M⊙ is implied. The nondetection of Hα and Hβ emission lines suggests a white dwarf star was disrupted, although the presence of strong nitrogen emission is somewhat of a mystery. Subject headings: Galaxies: Individual: NGC Number: NGC 1399, Galaxies: Star Clusters, Galaxy: Globular Clusters: General, X-Rays: Binaries, X-Rays: Galaxies: Clusters