High-Resolution X-Ray Spectroscopy of RX J0806.3+1527 with Chandra

Abstract

RX J0806.3+1527 is a candidate double-degenerate binary with possibly the shortest known orbital period. The source shows an ≈100% X-ray intensity modulation at the putative orbital period of 321.5 s, but there still is no direct detection of orbital motion at this period. Here we report the results of high-resolution X-ray spectroscopic observations of the source, obtained with the Chandra Low Energy Transmission Grating (LETG) spectrometer. We obtained a total of ≈80 ks of exposure in two pointings separated by about 5 months. We detect the source in both the zeroth-order image and the dispersed spectrum. Detection of the 321.5 s pulsations in the zeroth-order image allows us to extract dispersed spectra as a function of the pulse phase of the X-ray modulation. The bulk of the source flux appears in the 20-60 A band. We find evidence for emission features in the 25-50 A range. The strongest feature (detected at better than 3 σ confidence) is an ≈0.6 A-wide (FWHM) emission line centered at 27 A. Weaker features at 31.6 and 46.4 A are also suggested, but they require confirmation with deeper exposures. The continuum is adequately described by an absorbed blackbody model with a temperature of 65 ± 5 eV and column depth of (2 ± 0.5) × 1020 cm−2. Interestingly, the spectrum does not show strong emission lines of typically abundant elements such as carbon, nitrogen, oxygen, and neon. We briefly discuss possible identifications for the emission features.