Chandra Astrometry of a New ULX in NGC 891

A 08/2011 XMM observation of NGC 891 shows a bright (L_X ~ 2E40 erg/s; F_X ~ 1E-12 erg/s/cm^2) new ULX near the disk. It is absent in archival X-ray observations. Variability in Swift monitoring and the absence of bright optical or radio counterparts rule out a SN. As a bright ULX that recently "turned on" and whose spectrum indicates a hot (kT ~ 1 keV) disk, the source may be an extreme example of super-Eddington (5-50 L_Edd) accretion. Deep archival HST images reveal a potential counterpart--a star cluster--within the 2" X-ray error circle, but it is only 0.5" across. A better position is a prerequisite for proposing deep spectroscopic follow-up, and the lack of radio or optical counterparts in follow-up observations makes CXO the only option. We expect an ACIS-S count rate of 0.07-0.2 cts/s, and request 2 ks of DDT time to obtain 150-400 cts, thereby sampling the PSF extremely well. Although a snapshot is susceptible to flaring, the ULX is extremely bright.