Multiwavelength spectral and high time resolution observations of SWIFT J1753.5−0127: new activity?

We have conducted an extensive observational campaign of SWIFT J1753.5−0127 during 2007 June after its bright outburst episode in 2005. We have performed multiband optical photometry, optical spectroscopy, X-ray spectroscopy and timing and ULTRACAM optical photometry simultaneously in three bands. Both the optical spectrum and the X-ray spectrum along with enhanced brightness in broad-band photometry point to recent increased activity. We analyse the different spectral regions, finding a smooth optical continuum with a remarkable lack of lines and a very blue component modulated with a period of 3.2 h and a hard power-law X-ray spectrum. Both the X-ray and optical power spectra are flat at low frequencies up to the 0.1 Hz (10 s) range, then decreasing roughly as a power law consistent with flickering. Furthermore, the optical data show quasi-periodic oscillations near 0.08 Hz (13 s). Together with a dynamical and autocorrelation analysis of the light curves we attempt to construct a complete physical picture of this intriguing system.