Astrophysical Fluids of Novae: High Resolution Pre-decay X-Ray Spectrum of V4743 Sagittarii

Abstract

Eight X-ray observations of V4743 Sgr (2002), observed with Chandra and XMM-Newton, are presented, covering three phases: Early optically thin hard emission (day 50.2), photospheric emission from the ejecta (days 180.4, 196.1, 301.9, 371, 526), and faint post-outburst emission (days 742 and 1286). The flux level at Earth during the first and last phase is of order $10^{-12}$ erg cm$^{-2}$ s$^{-1}$ over the energy range 0.3–2.5 keV. These values are higher than an upper limit obtained in September 1990 with ROSAT. The nova thus continued fading in the soft band (0.1–2.4 keV). The nova turned off some time between days 301.9 and 371, and the X-ray flux subsequently decreased from day 301.9–526, following an exponential decline time scale of $(96 \pm 3)$ days. We use the absorption lines present in the SSS spectrum for diagnostic purposes, and characterize the physics and the dynamics of the expanding atmosphere during the explosion of the nova. The information extracted from this first stage is then used as input for computing full photoionization models of the ejecta in V4743 Sgr. The SSS spectrum is modeled with a simple black-body and multiplicative Gaussian lines, which provides us of a general kinematical picture of the system, before it decays to its faint phase (Ness et al. 2003). In the grating spectra taken between days 180.4 and 370, we can resolve the line profiles of absorption lines arising from H-like and He-like C, N, and O, including transitions involving higher principal quantum numbers. Except for a few interstellar lines, all lines are significantly blue-shifted, yielding velocities between 1000 and 6000 km $\mathrm{s}^{-1}$ which implies an ongoing mass loss. It is shown that significant expansion and mass loss occur during this phase of the explosion, at a rate $\dot{M} \approx (3-5) \times 10^{-4} ~ (L/L_{38}) ~ M_{\odot }/yr$. Our measurements show that the efficiency of the amount of energy used for the motion of the ejecta, defined as the ratio between the kinetic luminosity $L_\mathrm{kin}$ and the radiated luminosity $L_\mathrm{rad}$, is of the order of one.