A Chandra low energy transmission grating spectrometer observation of V4743 Sagittarii: A supersoft X-ray source and a violently variable light curve

J. U. Ness, S. Starrfield, V. Burwitz, R. Wichmann, P. Hauschildt, J. J. Drake, R. M. Wagner, H. E. Bond, J. Krautter, M. Orio, M. Hernanz, R. D. Gehrz, C. E. Woodward, Y. Butt, K. Mukai, S. Balman, J. W. Truran

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V4743 Sagittarii (Nova Sgr 2002 No. 3) was discovered on 2002 September 20. We obtained a 5 ks ACISS spectrum in 2002 November and found that the nova was faint in X-rays. We then obtained a 25 ks Chandra Low Energy Transmission Grating Spectrometer (LETGS) observation on 2003 March 19. By this time, it had evolved into the supersoft X-ray phase exhibiting a continuous spectrum with deep absorption features. The light curve from the observation showed large-amplitude oscillations with a period of 1325 s (22 minutes) followed by a decline in the total count rate after ∼13 ks of observations. The count rate dropped from ∼40 counts s-1 to practically zero within ∼6 ks and stayed low for the rest of the observation (∼6 ks). The spectral hardness ratio changed from maxima to minima in correlation with the oscillations and then became significantly softer during the decay. Strong H-like and He-like lines of oxygen, nitrogen, and carbon were found in absorption during the bright phase, indicating temperatures between 1 and 2 MK, but they were shifted in wavelength corresponding to a Doppler velocity of -2400 km s-1. The spectrum obtained after the decline in count rate showed emission lines of C VI, N VI, and N VII, suggesting that we were seeing expanding gas ejected during the outburst, probably originating from CNO-cycled material. An XMM-Newton Target of Opportunity observation, obtained on 2002 April 4 and a later LETGS observation from 2003 July 18 also showed oscillations, but with smaller amplitudes.

Original languageEnglish (US)
Pages (from-to)L127-L130
JournalAstrophysical Journal
Issue number2 II
StatePublished - Sep 10 2003

Bibliographical note

Funding Information:
J.-U. N. acknowledges support from DLR under 50OR0105. S. S. received partial support from NSF and NASA grants to ASU. J. J. D. and Y. B. were supported by NASA contract NAS8-39073 to the Chandra X-ray Center (CXC). S. S., R. M. W., P. H., J. W. T., R. D. G., and C. E. W. were partially supported by grants from the CXC to their various institutions. Finally, we would like to thank the mission planners and staff of the CXC for their flawless scheduling and execution of this ToO program.


  • Novae, cataclysmic variables
  • Stars: individual (V4743 Sagittarii)
  • Stars: oscillations
  • White dwarfs
  • X-rays: binaries


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