The Unusual X-Ray Spectrum of Nova V1716 ScorpII
Abstract
V1716 Sco (Nova Sco 2023) was observed in outburst on 2023 April 20 as a moderately fast nova. It has been observed in X-rays with Swift, NICER, and Chandra; we present here recent spectra taken with the Chandra Low Energy Transmission Grating (LETG) in 2023 August 26 and 27, after a luminous supersoft X-ray source was detected with the Swift X-Ray Telescope (XRT) and with NICER (Astronomer's Telegram 1609, Page et al.2023, and 16167, Dethero et al. 2023). The high resolution LETG grating spectra revealed that there is almost no continuum in the X-ray spectrum and most of the supersoft flux is in broad, prominent emission lines. Although an emission line spectrum has been observed in other novae in the supersoft X-ray phase (Ness et al. 2013, ApJ, 769, L4), the lines of V1716 Sco are unusual and not typical of a thermal plasma in collisional ionization equilibrium. There is a particularly prominent emission line of O I at 23.5 Å, broadened by approximately 3000 km/s, never observed in other novae in outburst. The light curve revealed that the -78 s QPO measured by Dethero et al. 2023 with NICER is still present. Such a short period modulation has been often measured in novae with higher X-ray supersoft flux and with a spectrum dominated by continuum and broad absorption features of the heated white dwarf atmosphere, but not in emission line spectra originating in the outflowing material like in V1716 Sco. The nova had recently brightened in supersoft X-rays (Astronomer's Telegram 16150 by Page et al. 2023) and new LETG observations are planned on October 20-22.
- Publication:
-
American Astronomical Society Meeting Abstracts #243
- Pub Date:
- February 2024
- Bibcode:
- 2024AAS...24346112W