Supersoft X-ray rebrightening of Nova Mon 2012
K. L. Li and A. K.H. Kong (National Tsing Hua University, Taiwan)
We report ten consecutive Swift follow-up observations of Nova Mon 2012 (ATel #4590). The first six observations were performed daily from 2012 November 23 to 2012 November 28 (~2 ks exposure per day) and the last four observations (~1 ks each) were taken on 2012 November 29. All Swift/XRT data are in the Photon Counting (PC) mode. The supersoft X-ray emissions from Nova Mon 2012 were still very bright in all of the proposed Swift X-ray observations. Similar to the first supersoft X-ray detection (ATel #4590), the energy spectra could be well described with an absorbed blackbody plus thermal plasma model (i.e., wabs*(bbodyrad+apec)) with N_H=9.6(+0.5/-0.6)e21cm^-2. Among the seven-day observations, the thermal plasma component stays stable with T_apec=1.06 (+0.06/-0.04) keV and F(0.8-10 keV)=4.25(+0.17/-0.18)e-12 ergs/cm^2/s while the blackbody component kept evolving rapidly. By assuming that the photosphere of the blackbody did not change significantly with time during the monitoring campaign (i.e., the optically thick wind has stopped), we get the best-fit temperatures (in eV) and observed supersoft X-ray fluxes (0.2-0.8 keV; in 10^-12 ergs/cm^2/s) as follows (including the spectral fitting of the first supersoft Swift/XRT observation): 2012-11-18: 30.4 (+1.6/-1.6) & 4.67 (+0.81/-0.69) 2012-11-23: 29.6 (+1.5/-1.5) & 3.09 (+0.52/-0.42) 2012-11-24: 29.2 (+1.5/-1.5) & 2.40 (+0.40/-0.35) 2012-11-25: 28.1 (+1.4/-1.4) & 1.21 (+0.25/-0.20) 2012-11-26: 27.3 (+1.4/-1.4) & 0.74 (+0.39/-0.24) 2012-11-27: 27.1 (+1.3/-1.4) & 0.68 (+0.24/-0.19) 2012-11-28: 30.0 (+1.5/-1.6) & 3.83 (+0.53/-0.45) 2012-11-29 (01:29): 30.2 (+1.6/-1.6) & 4.18 (+0.85/-0.71) 2012-11-29 (11:03): 30.8 (+1.6/-1.6) & 5.96 (+0.81/-0.70) 2012-11-29 (17:27): 31.3 (+1.6/-1.6) & 7.62 (+0.91/-0.85) 2012-11-29 (22:08): 28.6 (+1.5/-1.5) & 1.67 (+0.60/-0.44) (XRT spectra. Different colors represent different epochs.) In the first six fits (from 2012 November 18 to 2012 November 27), the supersoft X-rays drop significantly with a decreasing best-fit temperature. However, the supersoft X-rays re-brightened unexpectedly in the seventh fit (2012 November 28), which is possibly due to some rapid activities on the white dwarf surface. On 2012 November 29, the soft X-ray flux continuously increased to a peak of 7.62(+0.91/-0.85)e-12 ergs/cm^2/s but suddenly returned to 1.67(+0.60/-0.44)e-12 ergs/cm^2/s in the last observation taken about 20 hours later. More multi-wavelength follow-up observations are strongly encouraged. We would like to thank the Swift team for scheduling the observations.
x-ray,nova