Superluminal Radio Jets from the 1999 September 14-15 Outburst of XTE J1819-254 (=V4641 Sgr=SAX J1819.3-2525)
The 1999 September 14-15 X-ray transient event in XTE J1819-284 lasted less than day, as did the the decay of an optical flare. This outburst produced a 0.4 Jy radio event that was strong for only about a day while it was ejecting jet radio emission with proper motion rates up to 0.5 arcseconds per day - making this the largest proper motion rate seen in any astronomical object outside the environs of our Solar System. During the first day the radio emission was observed by seven radio telescopes: GBI, VLA, ATCA, MOST, OVRO 40 meter, MERLIN, and RATAN 600. It was a resolved radio source for the VLA within hours of the strongest, 12 Crab X-ray outburst. The sensitive radio telescopes were able to follow a decay, from 0.4 to 0.00012 Jy, of 0.24[ν GHz-0.75(MJD - 51436.9)-1.9] until 1999 October 7 - after which it was too weak to observe. The HI absorption against the XTE J1819-284 radio source indicates a distance of 500 pc or more; this and other considerations make the distance likely to be near 500 pc, making XTE J1819-284 the closest X-ray transient ever to be observed in outburst, and in part explaining its unusual strength. The radio light curves are fit by a highly relativistic, conical twin-jet model with v 0.9c, so the approaching and receding jets have apparent velocities of 1.5c and 0.6c, respectively, making XTE J1819-254 the fourth, and by far the nearest, Galactic superluminal source. If the others, GRS 1915+105, GRO J1655-40, and XTE J1748-288, had been at a distance of 500 pc their apparent proper motion rates would have been 0.52, 0.41, and 0.46 arcseconds per day.
American Astronomical Society Meeting Abstracts #195
- Pub Date:
- May 2000