Abstract

Since the launch of the Chandra X-ray Observatory in 1999, broad x-ray surveys have been the primary means of discovering new objects in the sky. We present the results of one such survey, examining variable x-ray sources in archival Chandra data. Our survey maximizes the possibility of finding novel and interesting sources by searching for all x-ray variable sources and manually categorizing variable objects. This allows for the identification of interesting objects with common classifications, like a typical galaxy with unusual fluctuations. To further increase the probability of finding sources we focused on galaxy clusters, allowing us to look at over a thousand galaxies per observation. Our analysis was based on a previously compiled database of source fluxes, over all available observations and across energies from 0.2 keV to 12 keV. We converted the soft x-ray flux (0.5 to 2 keV) to count rate, then fit it to the average count rate using least squares regression. Variable sources are defined as those with 2 > 50 over the total observed time. We then categorized variable objects and found optical counterparts. Our criteria identified 49 variable sources from a total of 58,000 sources in our database, though we estimate up to 20% of the database is extraneous double sources. Of these variable sources, 9 had not been previously identified in the SIMBAD database and 28 had not been previously categorized as variable. A majority of the objects found were expected, such as various classes of active galactic nuclei and variable red dwarfs. Other more interesting objects include a variable A-type star and an ultraluminous galaxy.