Chandra observations reveal a rich absorption line system in the supersoft X-ray spectrum of V339 Del (Nova Del 2013)
ATel #5593; T. Nelson (Minnesota), K. Mukai (NASA/UMBC), L. Chomiuk (MSU) and J. Sokoloski (Columbia)
on 22 Nov 2013; 23:22 UT
Credential Certification: Thomas Nelson (tnelson@physics.umn.edu)
Following the report of the emergence of a bright supersoft X-ray source in V339 Del (see ATEL #5505), we obtained a high resolution X-ray spectrum of the nova with the LETG/HRC-S instrument on board the Chandra observatory starting on 2013 November 09.75 (88 days after discovery). The observation had a net exposure time of 46 ks, during which the source was detected in the 22--44 Angstrom range with a mean count rate of 21 (24) cts/s in the +1 (-1) order light. The nova did not exhibit the large scale variations in count rate previously detected by Swift (ATEL #5573), and a preliminary timing analysis did not find the 54 s QPO in the power spectrum.
The high signal-to-noise Chandra spectrum reveals a rich system of absorption lines superimposed on a supersoft continuum source - no emission lines are present. We identify the deepest absorption features in the spectrum as lines of hydrogen- and helium-like carbon and nitrogen, and the strongest lines appear to be blueshifted by ~1200 km/s. Other weaker absorption lines are also present. We detect no X-ray flux at wavelengths shorter than 22 Angstroms---the total observed flux in the energy range 0.1 - 1 keV is 2.8e-9 erg/s/cm^2. Modeling the data as a simple absorbed blackbody, we find an interstellar absorbing column of 1.8 x 10^21 cm^-2, and a photospheric temperature of 27 eV (~310000 K). However, we caution that the model fit is statistically poor and that blackbody fits to supersoft spectra in novae are known to substantially underestimate the temperature.
A second Chandra observation is planned on 2013 December 2. We would like to thank Harvey Tananbaum and the Chandra observatory for their help in scheduling these observations.
