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State Transition of GX 339-4

ATel #120; D. M. Smith, E. Kalemci (Space Sciences Laboratory, U. C. Berkeley), J. A. Tomsick, W. A. Heindl (Center for Astrophysics and Space Science, U. C. San Diego)
on 25 Feb 2003; 02:22 UT
Distributed as an Instant Email Notice Request For Observations
Credential Certification: David M. Smith (dsmith@ssl.berkeley.edu)

Subjects: Radio, X-ray, Gamma Ray, Request for Observations, Black Hole, Transient

Referred to by ATel #: 196

The black hole candidate GX 339-4, in outburst for nearly a year (ATEL #85) has lately been declining rapidly in luminosity in the soft state and has now started to show signs of a transition to the low/hard state. We have been monitoring this source twice weekly with the Proportional Counter Array (PCA) on the Rossi X-ray Timing Explorer. As of 23 February, 17:30 UT, the power law component of the spectrum now dominates the 3-25 keV count rate. The root-mean-squared variability (beyond Poisson statistics) is low, only 2.4%, yet this is higher than has been seen in the soft state for the last few months. Radio and x-ray observations are particularly encouraged over the course of this week, which should find the source in a truly transitional phase.