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New Chandra observation of Nova Mon 2012

ATel #4633; Marina Orio (University of Wisconsin, Madison WI, USA and INAF-Padova, Italy) and Ben Tofflemire (University of Wisconsin, Madison, WI, USA)Pa
on 10 Dec 2012; 11:08 UT
Credential Certification: Marina Orio (orio@astro.wisc.edu)

Subjects: X-ray, Nova

Referred to by ATel #: 4709, 4727, 4737

We report the results of a a Chandra high-resolution X-ray grating spectrum of Nova Mon 2012 (ATel #4310, #4320, #4321, #4352, #4365, #4376, #4408, #4542, #4569, #4572, #4590), done on 2012, December 3, 439 days after the maximum recorded at optical wavelength with the High Resolution Camera and Low Energy Transmission Grating (LETG). The exposure time was a little more than 7 hours. The average LETG count rate in the summed +1 and -1 orders was 0.210+-0.016 counts/s, but the source of X-rays was variable by almost an order of magnitude over the whole exposure. The light curve shows a smooth variation during the exposure, possibly an orbital modulation. The spectrum is complex, with at least three different components. The hot plasma observed on 2012 September 12 (ATel 4569) has cooled (kT<=3 keV), but emission lines of neon and magnesium are still strong. There are also prominent, red-shifted emission lines of H-like and He-like transitions of oxygen and nitrogen in the soft range, either caused by collisional ionization in a much cooler plasma (kT<400 eV), or due to photoionization of the central source. A high continuum level and absorption features in the 20-30 eV range are consistent with a hot white dwarf with an effective temperature around 750,000K, a column density exceeding 2.5 x 10(21)/cm(2), and unabsorbed flux of only a few times 10(-10) erg/s/cm(2). The derived flux is less than 1/100th the flux of a hot compact white dwarf at the derived temperature and assuming a 1.4 kpc distance (ATel #4352). While these results are preliminary, they may indicate ``holes'' of lower absorption in the ejecta, while most of the nova shell is still optically thick to the X-rays of the central source, or a Compton scattering corona reflecting the light of a hidden white dwarf in a high inclination system.