State Changes in GX 339-4
ATel #95; D. M. Smith, Space Sciences Laboratory, U. C. Berkeley; T. Belloni, Brera Observatory, Italy; W. A. Heindl and E. Kalemci, Center for Astrophysics and Space Science, U. C. San Diego; R. Remillard and M. Nowak, MIT; J. H. Swank, NASA Goddard Space Flight Center; and S. Corbel, Universite Paris VII and CEA Saclay
on 20 May 2002; 18:20 UT
Distributed as an Instant Email Notice Request For Observations
Credential Certification: David M. Smith (email@example.com)
Subjects: X-ray, Gamma Ray, Binary, Black Hole, Transient
Referred to by ATel #: 196
Using recent data from the Rossi X-ray Timing Explorer, we find that
the black hole candidate GX 339-4, in outburst since March 26 (see
ATEL #85), entered the Very High State (VHS) around May 6, a rare
state of x-ray emission last seen in this object in 1988 (Miyamoto et
al. 1991, ApJ 383, 784). The VHS may be the same as the "Intermediate
State" (IS) identified by some authors.
The energy spectrum is roughly
consistent with the sum of a power law of photon index -2.5 and a disk
blackbody with maximum temperature 1 keV. The contribution of
the thermal component has been increasing:
the 2-50 keV luminosity of
2x10-8 ergs/cm2/s was equally split between these components on May
16, with the thermal component carrying about 2/3 of the luminosity
by May 18.
spectrum from May 6-16,
similar to the 1988 Ginga observations,
showed flat-topped noise with a
break around 1 Hz and a strong quasi-periodic oscillation
that moved from 0.6 to 9 Hz as the state has evolved.
The most recent observations have shown a greater
variety of behavior, including a strong amount of red noise
in one observation on May 17 and a short pointing on May 18 which
showed almost no variability at all (rms 1.7%). This may indicate
that the state has left the VHS/IS entirely and entered the high/soft
state (HS), or it may simply be part of the unpredictable shifts in
behavior which often characterize the VHS.
Prompt observations at all wavelengths are encouraged, whether
the current state is still VHS or is now HS.
Since the VHS in other black-hole candidates
has show a wide range of behaviors, frequent observing could be