Chandra high resolution X-ray spectroscopy of Nova Ret 2020

ATel #14214; Jeremy J. Drake (CfA-Harvard & Smithsonian), Marina Orio (University of Wisconsin and INAF-Padova), Andy Bearmore (University of Leicester), Ehud Behar (Technion), Gerardo Juan Manuel Luna (COMICET-University of Buenos Aires), Jan-Uwe Ness (ESA-ESAC)
on 24 Nov 2020; 23:25 UT
Distributed as an Instant Email Notice Novae
Credential Certification: Marina Orio (orio@astro.wisc.edu)

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Nova Ret 2020 (MGAB-V207, YZ Ret; see ATels #13867, #13868, #13874, #14043, #14048, #14067) was observed with the Chandra HRC-I camera and Low Energy Transmission Grating (LETG) on 2020-10-31 at 07:31:26 UT, for a total exposure time of about 30 kiloseconds. At that time, the X-ray luminosity had decreased by more than an order of magnitude since the observations mentioned in ATel #14067. The source was nevertheless detected and the resulting spectrum was extremely soft, with signal only securely in evidence longward of 20 Å. The average count rate of the coadded +1 and -1 orders measured with the LETG was 0.080 ± 0.005 counts/s in the 20-70 Å range. The measured flux in this range is about 1.13 x 10^-11 erg/cm²/s, indicating X-ray luminosity of about 10³⁴ erg/s at the distance of 2.7^+0.4_-0.3 kiloparsec, based on the GAIA parallax ( Bailer-Jones et al. 2018 ). The X-ray signal was steady, with no significant variability or periodicity. The spectrum was inconsistent with that of a white dwarf atmosphere and instead comprised many emission lines, mostly in the 30-75 Å range, that we tentatively identify with transitions of iron, argon, silicon, magnesium, sulphur, carbon and nitrogen. The observed emission is most likely originating in the ejecta with a characteristic temperature of the order of 10⁶ K. Unlike in other novae, the spectrum deviates significantly from that of a plasma in collisionally-ionized equilibrium with solar-like abundances, possibly indicating photoionization or non-equilibrium conditions.