All Tables

Table 1: Best-fit spectral parameters for the two segments of the XRT observation (WT and PC data), fitted both separately and together. We report the results either leaving the hydrogen column density as a free parameter, or freezing it to the Galactic value.
Table 2: The spectral parameters as measured separately by XMM-Newton and XRT, fitting the data both separately and together. For this fit, XRT data were selected from the same time interval covered by the XMM-Newton observation. Due to the limited statistics, $N_{\rm H}$ was frozen to the value derived by XMM-Newton when fitting XRT data. The errors are at 90% confidence level for a single parameter of interest.
Table 3: Summary of optical and ultraviolet observations. All data but the point in the R band were measured by Swift-UVOT. The R-band observations is by Tristram et al. (2005). All measurements were corrected for the Galactic extinction ( $A_{\rm V} = 0.123$ mag; Schlegel et al. 1998), assuming the Milky Way extinction curve by Pei (1992). The optical-to-X-ray spectral index is $\beta_{\rm OX} = \log(F_\nu^{\rm opt}/F_\nu^{\rm X}) / \log(\nu_{\rm X}/\nu_{\rm opt})$ . The X-ray frequency was set to $\nu _{\rm X} = 1.5$ keV, the logarithmic mean of the XRT observing range. The X-ray flux was computed by interpolating the XRT light curve to the time of the optical limit. The last column reports the ratio of the extrapolated X-ray flux to the optical one (assuming no spectral breaks between the two bands; see Fig. 7).