Full-band (E = 0.5−10 keV) light curve using ASCA data (blue triangle), XMM-Newton (red squares), our Swift-XRT campaign (black circles), and additional archival Swift-XRT observation (magenta star; left). Time variability of the hardness ratio HR = (H − S)/(H + S), where S and H are the 0.5 − 2 and 2 − 10 keV count rates, respectively (left). The spectrum in the most recent data is noticeably harder. The count rates of the ASCA and EPIC-pn observations were converted into Swift-XRT count rates following the procedure described in Sect. 3.