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J. H. Swank, T. E. Strohmayer (NASA/GSFC), C. B. Markwardt (UMD, NASA/GSFC)
On 2003 January 9, XTE J1720-318 appeared in the data from the All Sky Monitor (ASM) on the Rossi X-Ray Timing Explorer (RXTE). It had already reached 350 mCrab after a rise of less than 1 day, and was already in a soft or thermal-dominant state. For 4 days the 2-10 keV X-ray flux varied between this value and a peak of 450 mCrab, before starting a decline over 200 days. Proportional Counter Array (PCA) and High Energy X-Ray Timing Experiment (HEXTE) observations began near the end of the peak. A radio transient found at the same time strengthens the identification as a black hole transient and an infrared transient implies information will be forthcoming about the binary system. An XMM-Newton observation was made a few hours after a set of RXTE observations, while the source was still in the soft state. Two flares occurred during the decay. The first was accompanied by little change in spectrum, but the second was associated with a change to a low hard state, as was reported to have also been detected with Integral. The hard source dropped by steps over 140 days before it was below an RXTE sensitivity limit of 0.5 mCrab, in mid-August. The evolution of the spectrum, luminosity, and timing properties will be presented.
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Bulletin of the American Astronomical Society, 35#5
© 2003. The American Astronomical Soceity.