SIMBAD references

Before the official first-light images, the Chandra X-Ray Observatory obtained an X-ray image of the field to which its focal plane was first exposed. We describe this historic observation and report our study of the first Chandra field. Chandra's Advanced CCD Imaging Spectrometer (ACIS) detected 15 X-ray sources, the brightest being dubbed Leon X-1 to honor the Chandra telescope scientist Leon Van Speybroeck. Based on our analysis of the X-ray data and spectroscopy at the European Southern Observatory (ESO; La Silla, Chile), we find that Leon X-1 is a type-1 (unobscured) active galactic nucleus (AGN) at redshift z=0.3207. Leon X-1 exhibits strong Fe II emission and a broad-line Balmer decrement that is unusually flat for an AGN. Within the context of the eigenvector-1 correlation space, these properties suggest that Leon X-1 may be a massive (≥10⁹ M_☉) black hole, accreting at a rate approaching its Eddington limit.