A Reanalysis of High Resolution XMM-Newton Data of V2491 Cyg Using   Collisionally Ionized Hot Absorber Models
  We present a reanalysis of XMM-Newton Reflection Grating Spectrometer data of the classical nova V2491 Cyg obtained from two different pointings, 40 d and 50 d after outburst utilizing the SRON software SPEX version 2.05.04. We aim to model absorption components using hot collisionally ionized absorber models along with interstellar absorption (of gas and dust origin separately). We find blackbody temperatures in a range 61-91 eV for the continuum yielding a white dwarf mass of 1.15-1.3 M_sun. We derive two different hot absorber components with blueshifts yielding 2900-3800 km/s for the first (day 40) and 2600-3600 km/s for the second observation 50 days after outburst consistent with ejecta/wind speeds. The two collisionally ionized hot absorption components have temperatures kT_1 =1.0-3.6 keV and kT_2 =0.4-0.87 keV with rms velocities (sigma_v) 872 km/s and 56 km/s. These are consistent with shock temperatures in the X-ray wavelengths. V2491 Cyg shows signature of H-burning with underabundant carbon C/C_sun=0.3-0.5, and enhanced nitrogen N/N_sun=5-7 and oxygen O/O_sun=16-43. We find the equivalent hydrogen column density of the hot collisionally ionized absorbers in a range (0.6-18.0)x10^{23} cm^{-2} and (2.0-5.3)x10^{23} cm^{-2} on days 40 and 50 after outburst, respectively. Our fits yield the most adequate redchisq (range 1.8-2.9) up-to-date obtained for the modeling of high resolution X-ray data of V2491 Cyg. An additional photoionized absorber (third intrinsic absorber component) originating in the shell/ejecta improves the model fits with redchisq in a range 1.7-2.5, but shows only (1-0.1)% of the absorption by the collisionaly-ionized hot gas. Our analysis reveals a second blackbody component on day 50 with effective temperature 120-131 eV and effective radius about 10% of the WD which may indicate the onset of magnetic accretion. 
Solen Balman and Cigdem Gamsizkan
astro-ph.HE