GRO J1655-40 Rising Again
ATel #436; C. Markwardt (U. Maryland & NASA/GSFC), J. Homan (MIT), J. Swank (NASA/GSFC)
on 6 Mar 2005; 17:39 UT
Credential Certification: Craig B. Markwardt (craigm@lheamail.gsfc.nasa.gov)
Subjects: X-ray, Binary, Black Hole, Transient
Referred to by ATel #: 438, 440
RXTE has continued to observe GRO J1655-40 since Mar 1 (ATEL #433).
The X-ray flux reached an intermediate low point on Mar 2 (19-22
mCrab, 2-10 keV), and has since been rising, with fluxes of 27, 29, 39
and 44 mCrab on Mar 3.8-4.0, 4.0-4.1, 4.9-5.1, 5.7, respectively (UT).
Occasional dipping behavior is still present, with a maximum
amplitude of ~40%.
The spectrum has remained primarily a power law with photon index
1.4-1.6. As the flux has risen, there is evidence for a softer
component, consistent with a black body with a kT of ~1 keV.
A QPO has become more distinct. The centroid frequency of the QPO
has increased from 0.17 to 0.31 Hz. These spectral and temporal
changes may indicate a state change of the source is occurring.
