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

Abstract

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 ≃1.3 Ms 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′×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.