The Swift X-ray monitoring campaign of the center of the Milky Way

In 2006 February, shortly after its launch, Swift began monitoring the center of the Milky Way with the on board X-Ray Telescope using short 1-ks exposures performed every 1-4 days. Between 2006 and 2014 over 1200 observations have been obtained, accumulating to similar or equal to 1.3Ms of exposure time. This has yielded a wealth of information about the long-term X-ray behavior of the supermassive black hole Sgr A*, and numerous transient X-ray binaries that are located within the 25' x 25' region covered by the campaign. In this review we highlight the discoveries made during these first nine years, which include 1) the detection of seven bright X-ray flares from Sgr A*, 2) the discovery of the magnetar SGR J1745-29,3) the first systematic analysis of the outburst light curves and energetics of the peculiar class of very-faint X-ray binaries, 4) the discovery of three new transient X-ray sources, 5) the exposure of low-level accretion in otherwise bright X-ray binaries, and 6) the identification of a candidate X-ray binary/millisecond radio pulsar transitional object. We also reflect on future science to be done by continuing this Swift's legacy campaign, such as high-cadence monitoring to study how the interaction between the gaseous object 'G2' and Sgr A* plays out in the future. (C) 2015 Elsevier B.V. All rights reserved.