Upper panel: X-ray flux vs. time. Empty triangles are 2 − 10 keV Swift data, black triangles are 0.5 − 10 keV XMM-Newton data, while black squares are 0.5 − 10 keV Chandra data, blank circles are 0.5 − 10 keV Einstein 1980 and ASCA 1998 data (the latter two values are from Gelfand & Gaensler 2007). The X axis below the zero value displays two discontinuity in order to easily compare the recorded fluxes with that of Einstein (1980) and ASCA (1998). The empirically selected horizontal dashed lines highlight the distinction among different flux states (see Sects. 4.2 and 4.4 for details). Lower panel: 2 − 10 keV flux for the October 2008 (Israel et al. 2010) and January 2009 outburst. Dotted vertical lines represent the two outbursts trigger time. Errors in both panels are 1σ c.l. All reported fluxes are not corrected for absorption.